Modification of ATMOSPHERIC PARAMETERS 1.2 PRECIPITATION |
Type of knowledge |
Results and interpretation |
Observation and analysis methods |
References |
| Reconstructions | Alps (Dolomites, Italy): An increase of precipitation during the Subboreal period is also reported in literature. |
Goudie 1992 ; Orombelli & Ravazzi 1996 in Corsini & al 2000 - A | |
Central Europe: During winter, the cold and dry anomalies have dominated between 1566 and 1605 and during 220 years, from 1676 to 1896, with high pressure situations above Scandinavia which directed cold polar continental air flows to Central Europe (Negative NAO index). The frequent winter rigorous constitute one of the main characteristic of the LIA. The glacier tongues progressed through the valley, forest and even fields since the middle of the 16th century. After 1895, such situations occurrence decrease, excepting the 1936-1945 and 1956-1965 decades. This trend continued during the last three decades with very low frequency of cold winter months. Pfister highlighted that during spring, cold and dry anomalies were common during the last 500 years, especially between 1566 and 1885 with some peaks for the 1566-1575 and 1736-1745 decades. This last decade show a very high frequency of North meridian circulations, bringing winter conditions during April month in Switzerland, even during May (1740) and led to important economical problems. The cold summer anomalies frequently appeared during the 16th and 17th century, especially between 1566 and 1635 and between 1666 and 1695. Some durable blocking situations, notably because of North-West flows, bringing heavy snowy precipitations at high altitude, leading to the glacier advanced of this time. But each century experienced warm summer, especially for the 1536-1545, 1616-1625 and 1936-1945 decades. The dry and hot summer trend became more pronounced during the second half of the 20th century, also marked by an Alpine glacier retreat. The autumn anomalies occurred in form of cold and warm periods that alternates and tended to be equilibrated until the middle of the 18th century. Then, the cold autumn months dominated with strong anomalies occurring one to three time per decade until 1935.Then the mild and dry autumn months became more frequent, but since 1986, wet and warm anomalies have been observed; such situations have not been observed significantly during the previous 500 years. |
The temperature and precipitations anomalies have been evaluated using index from the validated series of Bâle (since 1756) and Genève (since 1768), developed by Pfister. The anomalies are determined by instrumental measures for the 1901-1960 period and using historical documents for the date pre-1755 (lake freezing date, grape harvest date …). |
Paul 2002 - A | |
French Alps (Rhone basin): |
Magny 2003 in Chapron & al 2005 - A | ||
Dolomites
(eastern Italian Alps): According to Goudie (1992) and Orombelli and Ravazzi (1996), starting from about 11,000 cal BP, a subsequent increase of precipitation took place, followed by a climatic optimum between 9000 and 5800 cal BP. Finally, around 2700 cal BP (at the Subboreal – Sub-Atlantic boundary), a sudden climatic worsening occurred, with a considerable increase of precipitation and widespread glacier advancement. |
Soldati & al 2004 - A | ||
Alpine Arc: Long-term precipitation variability shows several subregionally different features. Especially the Mediterranean part has sometimes even opposite trend signs versus the Atlantic subregion for several decades. Autumns have tended to be wetter over the 1980-2000 period. During the 1800-1850 period, wet autumns, winters and summers had been observed in contrast with dry springs. |
Precipitation annual, GAR and subregions, single year and 30 years low pass filtrered (1800-2003). Anomalies to 20th century mean.
|
Böhm et al. 2005 - A | |
| Alpine
Arc: |
High-resolution reconstructions of gridded temperature and precipitation patterns for the greater European Alpine region back to 1500 using long instrumental data in combination with documentary proxy evidence, with a spatial resolution of 0.5° × 0.5° equal to 199 grid points and complement recently established tree-ring based reconstructions over the European Alps or parts of it. Eighty seven early instrumental temperature and 146 precipitation time series from all over Europe in combination with 11 documentary records for temperature (precipitation) including estimates derived from narratives, annals, scientific writings and monastery records are used as predictors for the gridded reconstruction of the greater Alpine area climate. Thirty-one-year running correlations between the extended winter (DJFM) North Atlantic Oscillation Index (NAOI; Cook et al., 2002) and the Alpine extended winter (DJFM) temperature and precipitation time series from 1659 to 2000 were computed. Prior to 1659, only seasonal (DJF) Alpine reconstructions are available. |
Casty & al. 2005 - A | |
|
Observations |
Switzerland: Since 1975, the heavy precipitation frequency (above 70 mm/day on a minimal surface of 500 km²) increased to two times the 1901-1974 value, to reach today 3 event/year. The monthly precipitation mean comparison between the 1961-1990 period and the 1931-1960 show a 20% increase for the December, March and April months. But the July and September month show a 10% decrease. The winter precipitation increase seems to be strongest over the Western Switzerland (20%). Some precipitation excess have been observed for the Fribourg and Montreux stations during the 1934-1940 period and a strong precipitation increase has also been observed since 1978. |
Lateltin & al. 1997 - R: PNR31 | |
Swiss Valais: The number of extreme rainfall events capable of triggering debris flows in August and September has increased in the last three decades in the region of Ritigraben. (Similar trends are observed for the 20th Century in all regions of Switzerland.) |
An analysis of precipitation data of several climatological stations in August and September since 1966 (which is the observation period available) has been carried on. |
Rebetez & al 1997 - A | |
Switzerland: The greatest snowfall period during 3 days and the total amount of daily new snow during the whole winter remain stable, but show extreme variability from year to year. |
The winter climate was primarily investigated at Davos (96 year continuous time series with daily data). |
Schneebeli & al. 1997 - A | |
| Switzerland: A general precipitation increase has been observed for two decades (since 1977) in the Western part of Switzerland and also partially in the Ticino. It has been stated, but not systematically checked, that the precipitation of the last 20 years tend to be concentrated during the cold season (when they are the most efficient for mass movements triggering). |
Noverraz & al. 1998 - R: PNR31 | ||
Alps: The snow falls and the cold air flows of the 1999 winter occurred in usual delays. But the duration of the North-West flows and the huge amount of snow have been exceptional. Switzerland: On the Western and North-West parts of the country, the precipitation increased almost of 30% during the 20th century. This increase is not directly linked to the changes in the meteorological situations. It seems rather that with global warming the humidity increase is observed in all the meteorological situations. The wind speed increase may also play a rule. |
ProClim 1999 - E | ||
Swiss Alps:
No significant statistical trend or periodicity for the parameters analysed during the 20th century. No marked change in the distribution of extreme snowfall events. |
Day by day parameter (temperature, precipitations, cloud cover, wind direction and force, new snow (snow falling for 3 days), height and duration of snow cover) for three meteorological stations: Davos; Bever and Andermatt. |
Bader & Kunz 2000a - R : PNR31 | |
Switzerland: The rain which fell in the last 20 years tended to be concentrated on the cold season. Precipitation has increased by an average of 15-30% over the previous annual norm in Western Switzerland and to a lesser extent in Ticino. |
Bader & Kunz 2000e - R : PNR31 | ||
Bernese Alps: Precipitation records of the weather stations in the Bernese Alps do not show any clear trend and every climatological site has its own particular evolution. |
Keller & al 2000 - A | ||
Switzerland: A heavy precipitation (> 50 mm/day) increase has been highlighted for the whole Switzerland since 1973; this could be explained by the higher frequency of some cyclonic situations. |
Measures on 133 Swiss stations |
Fallot 2000 in Paul 2002 - A | |
| Europe:
General increase in Northern Hemisphere mid and high latitudes (particularly in autumn and winter) in the precipitation trends. Precipitation over northern Europe has increased by 10-40% in the 20th century, whereas some parts of southern Europe have dried by as much as 20%. |
IPCC 2001 - R (WG2) | ||
|
Swiss Alps:
For intense precipitation events, a seasonally distinct trend signal has been revealed. In spring and summer the trend results in the station sample are roughly balanced between increasing and decreasing estimates and there is only a small number of stations for which the trends are statistically significant. In contrast for winter and autumn the station charts suggest an increasing trend signal with a clear prominence of positive estimates. Trend results for extreme precipitation events show only few series for which trends are statistically significant. For the winter season there is a strong bias toward increasing trend estimates and a high portion of statistically significant increases in moderate and intense precipitation events. The spatial distribution of the trend is similar between the two event categories. The wintertime trend signal is then gradually less apparent for the more rare strong and extreme events. In the autumn season significant trends are found at a considerable portion of the sites for intense and strong events. In this case the trend analysis did not reveal a trend signal in the occurrence of moderate precipitation events. While the wintertime increase conforms to an increase of mean wintertime precipitation, the trend signal for autumn reflects mutually compensating long-term variations in the frequency distribution. Finally for spring and summer the results of the trend analyses do not exhibit conclusive trend signals at any of the event categories. For the station samples in the Alps, summer is the main
season of heavy precipitation (high threshold values), due to summertime
convection and heavy thunderstorms. More frequent heavy events occur to
the south of the ridge where local convection and topographic precipitation
linked to moist southerly airflows contribute to peak activities in summer
and autumn. The findings of this study confirm an earlier report on increasing heavy precipitation frequency in Switzerland. The observed increase of intense precipitation conforms to the ideas of an intensified water cycle and the observed long-term warming. |
In this study we present a statistical framework for the assessment of trends in rare weather events. The framework embraces both a trend test (consideration of type I errors) as well as a quantification of the potential/ limitation of trend detectability (type II errors). The methodology is based on the binomial process, which is adopted as a simple stochastic model for annual and seasonal counts of rare events. Trend estimation and testing is conducted using logistic linear regression. The potential of trend detectability, represented in the form of a detection probability, is quantified as a function of record length, trend magnitude, and event rarity. This is accomplished using the binomial process in Monte Carlo simulations of surrogate, ‘‘trendy’’ records. The dataset for this trend study is composed of daily precipitation series at 113 rain gauge stations in Switzerland. The data embrace all Swiss rain gauges for which a continuous and complete daily record is available throughout the 94-yr period 1901–94. |
Frei & Schär 2001 - A | |
French
Alps: For the 1984-1999 periode, precipitation maximum are found in the northwest part and decreases toward the southeast. A secondary maximum is located in the extreme southeast, associated with the occurrence of Mediterranean lows. |
Mean of snowfall analysed by SAFRAN at 1500 m asl |
Martin & al. 2001 - A | |
| European
Alps: Mean annual values of Alpine precipitation vary between 1.5 and 8 mm day-1 according to ANALYSIS. The main features of the spatial distribution are two high-precipitation bands extending along the northern and southern rim of the Alpine ridge, and drier conditions in the interior of the mountain range and over the adjacent flatland. The maximum along the southern rim is divided into two major wet zones, centered over southern Switzerland/northern Italy and over eastern Italy/Slovenia, respectively. The monthly precipitation patterns exhibit pronounced seasonal and interannual variations, as reflected in the standard deviation. Regions with high standard deviation coincide with regions of high annual means. Time reconstructions of seasonal precipitation means of the 5 leading RPCs for the period 1901-90 have shown a large variability on annual to multi-decadal time-scales. The magnitude of the interannual variability varies considerably between RPCs and between seasons. Various of the decadal-scale extrema and also some of the annual peaks are common between the corresponding principal components (PCs). According to linear precipitation trends for the 1901-90 period, an increase of winter precipitation by 20-30% per 100 years in the western part of the Alps, and a decrease of autumn precipitation by 20-40% to the south of the main ridge are detected. The correlation analysis reveals weak and highly intermittent correlations with the North Atlantic Oscillation Index to the north and more robust correlations to the south of the main Alpine crest. It implies that the increase of winter precipitation cannot be explained by the observed trend of the NAOI, at least in the framework of a simple linear regression model. The observation that precipitation changes in winter are primarily due to increasing precipitation activity rather than changes in the frequency of weather types and that the changes are associated with an increasing frequency of intense precipitation events lend some support to the hypothesis of an intensified water cycle. |
The reconstruction of the mesoscale precipitation fields is based on the reduced-space optimal interpolation method of Kaplan et al. The reconstruction and analysis of centennial precipitation variations proceeds from two datasets: • The high-resolution gridded dataset (ANALYSIS) consists of monthly precipitation fields for the period 1971-90 with a grid spacing of 25 km. It was derived from 6800 station records of the operational high-resolution rain-gauge networks in the Alpine region. • The sparse dataset comprises 140 long-term station records covering the period 1901-90. The network exhibits great difference in the density of the stations. The dataset was subjected to a rigorous homogenization procedure (Alexandersson test). The rotated principal components (RPCs) represent estimates of area mean precipitation anomalies. Loading patterns of the five leading RPCs of monthly precipitation for the years 1971-90 have been presented. The spatial distribution of linear trends of seasonal precipitation has been presented for the complete reconstruction (28 PCs), and compared to linear trends in the 5 leading RPCs. Linear precipitation trends for the period 1901-90 have been obtained from linear regressions for each of the grid points and using the full reconstruction dataset. Values of monthly NAOI have been taken from Hurrell (2000). |
Schmidli & al. 2001 - A | |
| Italy:
There is a clear dividing line between the Heavy-Torrential categories (C2, D1 and D2) which show an increasing trend, and the weaker categories (A, B, C1) which show a highly significant decreasing trend. The Heavy to Torrential contribution (C2 + Dl + D2), increases from 23% in the 1950s to about 31% from the total annual rainfall in the 1990s. Extreme dai1y rainfall increases in spite of the fact that total rainfall general1y decreases. For instance, torrential rainfall exceeding 128 mm/d contributes 4-5% of the total Italy rainfall in the 1990s compared to only 1% in the 1950s ; an increase by a factor of 4. Furthermore, heavy to torrential categories above 32 mm/d contributed in the 1950s only 23% of Italy rainfall and this share increased to 32% in the 1990s. Italy stations during 1880-1996 have shown similar trends for heavy rainfall contributed mostly by the rainfall in summer and in the transition seasons [Brunetti et al., 1999]. |
Data gathered for 42 Italian stations (part of the 265 stations used in the study for the Mediterranean zone) covering the 1951-1995 period. |
Alpert & al. 2002 - A | |
France: The precipitations have a trend at the edge of the significance: rather increasing and mainly on the already wet seasons. Only summer time shows a general precipitation decrease for the 1901-2000. Almost all the winter precipitation increase. For the other seasons, the decrease mainly concerns the Southern parts of the country. On the calculated series, two seasons can be identified. During winter time, most of the precipitation increase. One third of these increase are significant. During summer, a majority of decrease is observed (65%) but none is significant. The spring and autumn exhibit intermediary results. The autumn characteristics make it closer to winter (majority of increase). The spring characteristics make it closer to summer (one third of decrease). Summer is the only season with only decrease. The Martone signal shows no pronounced spatial coherence. However, the drought conditions are more important in the South (8 series of the South half show an index decrease) and most of the North index are increasing. The low site density limits the possible interpretation of the results. |
Long climatic series homogenization by identifying the homogeneity breaks in the series and break correction. The Martone index is calculated for the station with both precipitation and temperature series (17 stations over 15 departments). The higher the index is and the wetter is the climate. The significance is tested with the Spearman coefficient. |
Moisselin & Schneider 2002 - A | |
Europe: In winter, the indices related to heavy precipitation show an increase for most of the stations in central Europe, the UK, and Scandinavia, while most of the stations in Eastern Europe, Greece, and western Iberian Peninsula show the opposite trend. The number of stations showing an increase is generally greater than those showing a decrease. The maximum number of consecutive dry days shows an increase in the southern part of the region and a decrease in the north, with the increase generally greater than the decrease. In summer, most of the indices related to heavy precipitation show four NW-SE oriented regions of coherent change: positive trends across northern Scandinavia and Russia, negative across the UK and NE Europe, positive through SW Europe and negative across the northern Iberian Peninsula. In general, the number of stations showing increases and decreases are balanced with the average trend across the entire region near zero. Although a less coherent signal was found for the maximum consecutive dry days, most of the stations in the central part, southern Scandinavia and the UK show an increase. Switzerland: Germany: Northern Italy: France: |
[Framework: STARDEX project] Maximum and minimum daily temperatures were collected from a number of representative stations within the study areas. The time period for the study was set between 1958 and 2001, but for some of the study areas the period extended back to as early as the beginning of the 20th century, as in the case of Switzerland. In addition, both precipitation and temperature extremes were analyzed by UEA for Europe as a whole using data from 481 stations for the period 1958 to 2000. As the study was focused mainly on the changes in extremes, a number of extreme temperature and precipitation indices were defined. Many of the indices are based on thresholds defined on the basis of statistical quantities such as the 90th or the 10th percentiles. The base period for the calculation of such quantities was set between 1961 and 1990. This makes the indices applicable to a wide variety of climates as no arbitrary threshold values are used. The only exception is a fixed threshold value of 0°C used to define frost days; which is, of course, applicable to all climates. Precipitation related
indices analysed in the study (STARDEX Diagnostic Extreme Indices): |
Bárdossy & al 2003 - E | |
Swiss
Alps: The precipitation rates are much more difficult to asses with strong statistical noises, even when smoothed trough a 5 years filter. The only significant variations has been observed at the Säntis high elevation site with a 3.3 mm/day increase (1961-1990 as reference period) and corresponds to almost twice the average value. There are increasing trends of solid precipitation at high elevations, and increasing trends of liquid precipitations at low to medium elevations. Milder winters are associated with high precipitation levels than cold winters, but with more solid precipitation at elevations exceeding 1700-2000 m a.s.l and more liquid precipitation below. |
Data issued by MeteoSwiss.
The temperature and precipitation anomalies as a function of time have been analysed with the 1961-1990 period as reference and the use of a 5 years filter to remove the noisiness of interannual variability. |
Beniston et al. 2003b - A | |
Southern Europe (Ebro - Rhone - Pô basins): |
Duband 2003 - P | ||
Swiss Alps: As for most other snow parameters, from 1960 to 1980 the days with snowfall were mainly above average and then a decreasing trend began. This trend to less snowfall days becomes stronger with decreasing altitude. In all regions, the snowfall days in the 1980s are significantly higher than in the 1990s; in all except one region (R7) the 1960s are also higher, and in some regions (R1-R3, R6) even the 1970s are significantly higher than the 1990s. Regarding the number of days with HN > 10, 20 and 50 cm (dhn10-dhn50), low-lying stations do not always, rarely or never reach daily new snowfalls greater than 10, 20 or 50 cm every winter. Long-term trends are similar to dhn, but they become weaker with higher thresholds. Whereas for dhn10 only the 1980s differ significantly from the 1990s, for dhn20 no decade differs significantly from any other; and, because of the very few events, for dhn50 no long-term changes can be determined at all. It is hard to find decades with particularly high or low HN3 maxima; but the 1980s were largely above average and the 1990s rather below average. Looking at individual winters confirms the pronounced small-scale variability. Hardly any changes can be seen in the long-term development, neither for the whole Swiss Alps nor for single regions. However, looking at different altitude zones reveals that stations above 1300 m a.s.l. show a very weak rising trend, whereas stations below this tend to fall slightly. Only the very low foreland stations (< 650 m a.s.l.) show a marked drop since the early 1980s. |
A maximum number of consistent long-term snow series was selected all over the Swiss Alps, divided into seven snow climatological regions (R1-R7) and including the adjacent forelands. R1-R3: North Slope, R4 and R7: the interior areas of the Alps, R5: Grisons and R6: South Slope. The analyses are based on daily, manually measured snow depth (HS) and new snow (HN) data from the observational networks. Only consistent long-term (> 25 years) stations within the period of 1931-99 were considered. This results in a total of 140 HS stations and 120 HN stations. Trends on daily new snowfall are analysed for long-term changes. The seasonal sum of daily HN correlates (r = 0.88) with the mean seasonal snow depth and thus shows very similar trends to the HS mean. Therefore, the HN sum is not discussed further here. However, the number of days with snowfall above several HN thresholds > 0, 10, 20 and 50 cm (dhn, dhn10-dhn50) is investigated. Additionally, the annual maximum new snow sum of three successive days (HN3max) is taken as an indicator for heavy snowfall events and is often connected to periods with spontaneous climax avalanches. |
Laternser & Schneebeli 2003 - A | |
Switzerland: Standard precipitation and heavy precipitation events increased significantly during the twentieth century. In the Swiss Alps, solid precipitations tend to increase at high altitude sites while liquid precipitations tend to increase at medium and low elevation sites. These results are based on observation measures during 1931-2000 (Beniston & al 2002). |
OcCC 2003 - R | ||
Écrins and Devoluy massif: There is no significant variation from the annual mean precipitations taken since 1980, for all weather stations studied. A small increase in the amounts of rainfall in spring, summer and autumn since 1961 has been observed at MB station. Winter is the only season which shows a small decrease in precipitation for this period. However, these variations between 1960-1980 and 1980-2000 are not significant (Mann–Whitney test), whatever the meteorological station. The evolution between 1964 and 2000 of the ten highest daily totals rainfall occurring each year between 15/06 and 15/10 at StC has shown no significant difference above 20 mm/d. Above 30 mm the number of rain-days observed have increased significantly since the 1980s for the thresholds of 30 and 40 mm. At LS 13 events between 30 and 40 mm/d occurred between 1970 and 1985, as opposed to 29 after 1985. For the more intense events, the difference was less marked and not significant. |
In the Dévoluy area, data from La Salette (LS) meteorological station (1770 m asl), which provided temperature and precipitation data going back to 1965, have been analysed. For the Massif des Ecrins, Le Monétier-les-Bains (MB 1490 m asl) and Saint Christophe en Oisans (StC 1570 m asl) stations, whose data go back to 1961 and 1964 respectively, have been choosen. |
Jomelli & al. 2004 - A | |
| South
French Pre Alps: Precipitation variability in the French southern PreAlps between 1950 and 2000 has been characterised by very significant heterogeneity and no general trends could be found. Two rupture years have been observed in the precipitation mean: the year 1978 and 1982. 1978 marks the beginning of very wet springs and autumns. Precipitation variability in the South Alps is also characterised by very significant heterogeneity. Even if light trends have been noticed for some characteristics, no general trend could be really found. |
There is a low station density in the study area and an irregularity of the chronological series (station location change or no more use of the station). The data for some stations have been completed with corrected data from the CNRS (ER 30 data bank). The West zone of the area is better covered than the East zone (only 3 stations). |
Berthelot & al. 2004- E | |
French and Swiss Alps: Considering the snow annual mean, the extreme snow falls and the number of days with snow falls, the meteorological chronicles show no trend. For example, this statement can be done for Chamonix (1050m a.s.l), where the snow data are available since 1959. Very strong interannual variations and some year cycle can be identified. The most important daily snow falls have been observed during the 1990s decade, which is one of the less snowy decade. Some test realised on the data collected since the end of the 19th century (in Switzerland) or since the middle of the 20th century (in France) show the snow fall stability. Thus, the snow cover decrease can not be attributed to a snow fall decrease (of their intensity or the annual mean of snow falls). |
Comparison of snow fall data. No detailed information is given in the document. |
Ancey 2005 - E | |
World:
Aerosols are found to alter cloud physics in a manner that reduces precipitation downstream from the pollution source. This also reduces the snow particle rime growth, resulting in lower snow water equivalent. |
Results obtained
from direct field measurements. |
Barnett & al. 2005 - A | |
Switzerland: For precipitation, there is no indication of a significant increase or decrease in spring, summer or autumn at the 95% confidence level. However, significant precipitation trends are observed at most sites in winter and in some of the yearly series. A significant increase in yearly values can be seen at the stations of the Swiss Plateau (Berne, Zurich, Geneva) and in the series of Chaumont, representing the Jura mountains. The slopes of the trends range from 7 to 10% per 100 years. However, looking at a progressive analysis, it becomes clear that the trends are influenced strongly by the last few years with relatively high annual precipitation amounts. In winter, positive trends of 16 to 37% per 100 years are found for the stations north of the alpine main crest. The strongest increase is observed in the western part of Switzerland (Geneva, Chaumont). The beginnings of the trends in most of the series are around 1940 to 1950. Similar to temperature, the two sites situated south of the alpine main crest clearly differ from the other stations. There is no significant increase or decrease in the yearly or seasonal precipitation series of Lugano or Segl-Maria. |
Basle, Berne, Château-d'Oex, Chaumont, Davos, Engelberg, Geneva, Lugano, Säntis, Segl-Maria, Sion and Zurich stations have been selected, ranging from 273 to 2490 m a.s.l. The homogenization procedure THOMAS (tool for homogenization of monthly data series) can be divided into two main steps: the detection of inhomogeneities and the calculation of the adjustments. The procedure allows searching and adjusting of the shifts in mean and linear trends. The detection of inhomogeneities with THOMAS is a combination of metadata (station history) analysis and the use of 12 different homogeneity tests. Reference series are used to isolate the effects of station discontinuities from regional climate change. The significance of the adjustments is tested using the robust Wilcoxon rank sum test. The Kendall tau test is used as a non-parametric method to test the significance of trends. The homogenized data set was used to study annual and seasonal characteristics of the temperature and precipitation series in the period 1864-2000. All values used for trend analysis are anomalies from the 1961-90 mean value. The non-parametric Mann-Kendall test was applied for trend analysis. The analysis was not performed for Château d'Oex (T, P), Davos (T, P) and Säntis (P) because of incomplete data series in the 19th century. |
Begert & al. 2005 - A | |
Europe/Alps: A particular feature of the positive phase of the NAO index is that it is invariably coupled to anomalously low precipitation, particularly from late fall to early spring, in southern and central Europe (including the Alps and the Carpathians), while the reverse is true for periods when the NAO index is negative. In the case of the negative index threshold, over 50% of the values recorded in winter in Säntis exceed 90% relative humidity, while in the case of the positive threshold this level of relative humidity is exceeded only 35% during the winter months (results not shown here). There is thus a clear reduction in ambient moisture at high elevations. Since the early 1970s, and until 1996, the wintertime NAO index has been increasingly positive, indicative of enhanced westerly flow over the North Atlantic. Mean wintertime values for relative humidity and precipitation at Säntis were analised for four distinct periods of the 20th century (1901-1999, 1950-1999, 1975-1999, and 1989-1999). In terms of moisture, relative humidity has decreased in winter, with a bias of close to 10% in the period 1989-1999, resulting from the NAO forcing; mean DJF relative humidity would have otherwise remained relatively constant throughout the century. Precipitation is also seen to be considerably marked by the NAO forcing in the last decade of the 20th century, with a substantial drop of 20% of winter precipitation linked to the high and persistent NAO index recorded during this period. |
Beniston 2005b - A | ||
Alps: Radically wetter trends have been observed in autumn for the 1980-2000 period. During the 1800-1850 period, wet summers, autumns and winters, in opposition with dry springs, have been detected. |
Böhm & al. 2005 - R | ||
Mediterranean: Trends have been estimated from the scores of each eigenvector retained in all RPCAs. They are mainly non existant or non significant decreasing, even if a few monthly trends appear to be significantly diminishing, primarily during winter months, March in the Atlantic region, October in the Mediterranean Spain, December in the Lions and Genoa Gulfs, January, winter and the year in Greece, winter and the year in Italy and winter in the Near East and increasing in April in the two gulfs. Correlation coefficients between SDP>0.1mm and other indices have been computed: the significant trends seem mainly related to RD>10 mm, which represents a high percentage of the total rainfall amount. Greece is remarkable: SDP>0.1mm and >10mm decrease significantly during January, winter, the rainy season and the entire year whereas SDP>95 th percentile increases significantly, in accordance with the climatic change scenarios for the end of this century as does the decreasing of the total monthly and seasonal rainfall. |
The aim of the paper lies in the identification of possible significant linear trends at monthly, seasonal and annual timescales in the Mediterranean during the second half of the 20th century. Monthly and daily records of 63 stations have been used to elaborate several precipitation indices: sum of daily precipitation (SDP) for rainfall >0.1mm, >10mm and >95th percentile, of number of rainy days (RD) >0.1mm and >10mm and of mean daily precipitation (MDP) >0.1mm and >10mm. For each index the stations have been gathered together by Rotated Principal Component Analyses to determine 8 sub-areas which can be considered as identical for all the timescales at the spatial scale of the research. |
Norrant & Douguedroit 2005 - A | |
World/France: According to the IPCC (IPCC, 2001a), since about forty years the precipitation increased by 5 to 10 % on average in the upper part of the Northern Hemisphere. In France , according to Météo France observations (Moisselin et al., 2002), winter and fall precipitation increased, while summer precipitation rather decreased on average. |
ONERC 2005 - R | ||
Swiss Alps: The 2003 summer was the driest over the last 500 years. The Atlantic disturbances were pushed away further North by the blocking anticyclone above Northern Europe and reached the Alps only sporadically. |
ProClim 2005 - R | ||
| Ticino:
Winter and the beginning of spring are the periods of the year with least precipitations in the Ticino area. The overall precipitation exhibited no significant annual trend This result is consistent with previous studies such as Rebetez, 1999 and Schmidli and Frei, 2003. Relative humidity has decreased considerably on monthly and seasonal basis. |
Analysis of data from the two meteorological stations of Lugano and Lucarno
have been made for the 1971-2003 period. Relative humidity was recorded at 7am, 1pm, 7pm in both locations. |
Reinhard & al. 2005 - A | |
Greater Alpine Region (GAR): Large variability on interannual to centennial timescales is evident. Besides few common features in the different subregions, such as the wet earliest 2 decades, the minima in the second half of the 19th century and around 1950, and the distinct autumn-wetting in the recent 2 decades, there are many differences in the long-term behavior, as well as in the interannual variability. The amplitude of the interannual variability differs considerably among the subregions. This seems to be independent of the number of available stations involved in each subregional mean, because the number of stations per region is quite similar (52, 41, 48, and 51 series for NW, NE, SW, and SE respectively), and the subregion with the lowest number of available stations is that with the lowest variability (the NE region). The reason seems to be related more to geographical aspects, the northern subregions having a lower interannual variability than the southern ones. The interannual variability differs markedly also among seasons, winter and autumn being the seasons with the highest interannual variability. The annual precipitation amounts show the already mentioned general drying trend from the wet early 1800s to the dry mid 19th century in all subregions (with the exception of the SE with no data in the first 4 decades of the 19th century). Then, there is a marked splitting between a long-lasting wetting in NW (less pronounced in NE) and a long-term drying in the Mediterranean, which is more pronounced in SE, not really significant in SW. These long-term features of the annual precipitation amounts are the result of a few similar seasonal evolutions but numerous different ones. In northern subregions (NW and NE) there is an initial tendency toward a decrease in winter precipitation amount, from the beginning up to 1850s, followed by a long increasing tendency that stops in the 1970s. This is not evident in southern subregions, where no relevant long-term variations are visible up to the 1970s. On the contrary, the winter precipitation decrease, that characterizes the recent decades from the 1980s up to today, is a common feature of all subregions, being evident in both northern and southern ones (but weakest in the NW). In autumn, the most interesting aspects are the long decrease in precipitation amount that characterizes southern subregions from the beginning up to 1970s (in northern subregions there is also a decrease in this period, but it is not as clear as in southern subregions), and then a rapid increase that is evident in all subregions. The most prominent feature which distinguishes spring precipitation from the other three seasons is the complete absence of the wet earliest decades in the first part of the 19th century. As already mentioned, summer precipitation does not show prominent and long-lasting trends. They are more characterized by ups and downs on a decadal scale, more pronounced in SW. According to the described subregional differences, the all GAR-average analysis is not really representative of the entire area, when for example, inverse subregional long-term trends lead to a no-trend result for the average over the entire region. On the other hand, the few already mentioned ‘‘all-GAR-features’’ may well reflect the continental-to-global-scale background (after the elimination of the topographically forced enhancements/reductions explainable through the existence of the Alpine chain). Northern subregions show a positive trend in the total annual precipitation amount, even if it does not reach significant values. On the contrary, total annual precipitation has a negative tendency in southern subregions with highly significant values (5% and 4% per century in SW and SE respectively). On a seasonal basis, northern subregions reach significant positive trend values in winter (only for NW, with an increase of +9% per century) and in spring (both for NW and NE, with trends of +6% and +4% per century respectively). In summer and autumn the sign of the trend is negative but not significant. The strongest contribution to the negative trend of total annual precipitation for southern subregions comes from the autumn season, where the trends are significant for both southern subregions (14% and 10% per century for SW and SE respectively). SE shows a significant negative trend also in spring (9% per century). North Atlantic Oscillation (NAO) and GAR Precipitation: The most relevant results are for the winter season (DJF), with the well-known negative correlation between NAO and precipitation southward of the Alps. In the northern part of the region, the winter correlation is also negative, but not significant. The transition between strong and weak NAO influence is very sharp along the zonal part of the Alpine chain, less pronounced west of the Alps, and smoothest (and turning northward) in the eastern, more continental parts of the GAR. This points to an existing marked influence of the Alps with respect to NAO precipitation correlation. It is interesting to note that this situation is not representative of the whole 1866–2003 period, the correlation not being constant over time, in particular in the northern part of the Alps. The sequence of maps shows that there is a negative sign of the correlation over all the region, in the first map (late 19th century), which progressively assumes a north-south dipolar pattern that becomes clearer and clearer in the following maps from the 20th century. |
The 192 station series of the GAR were regionalized (via S-mode PCA, performed on the correlation matrix of normalized monthly/seasonal/annual precipitation totals) into four approximately equally sized principal subregions (NW, NE, SW, and SE). The different time evolution of precipitation in the various subregions was also highlighted by a T-mode PCA. This technique highlighted the existence of two leading general and long-term dipole structures, throughout north-south and west-east main directions. Series, representative of these two patterns, were constructed from the differences between northern and southern regional average series, and western and eastern ones. Besides changes in total precipitation amount, precipitation distribution over the year was also analyzed to identify changes in precipitation seasonality.
|
Brunetti & al 2006 - A | |
France: The precipitation evolution in France during the 20th century is characterised by increased annual rainfalls, except for South of France showing decreasing amounts of precipitation, especially located around the Mediterranean Sea. These results are consistent with the IPCC findings, i.e. a 0.5 to 1% precipitation amount increase per decade during the 20th century for the high and mid continental latitudes of North hemisphere […]. The precipitation evolution is changing depending on the season considered, with increasing winter precipitations and summer precipitation that tend to decrease. The precipitation amount for the 1951-2000 period show increased annual trend for the whole country, except for the stations located in the area from the Landes to the Mediterranean Sea where the precipitation amount tend to decrease. The increase trend is less obvious for the 1951-2000 than for the whole 20th century. The seasonal contrasts characterising the precipitation evolution for the 20th century are clear for the 1951-2000 period: winter precipitation increased in the 2/3 north of the country and decreased for the 1/3 south; the summer precipitation amounts decrease and the autumn and spring precipitation amounts increased in general and decrease for the Mediterranean part […]. |
Monthly series homogenisation using the method developed by Caussinus and Mestre 2004. There are 300 homogenised temperature centennial series, covering 51 department of Metropolitan France. Creation of the Daily Reference Series (SQR in French): Selection of daily series exploitable over a long period, on the basis of information issued by the monthly series homogenisation (date and amplitude of the homogeneity ruptures). Definition of the indexes characterising the extremes (indexes defined by the CLIVAR group in a way to enable the exchange and comparison of results). The indexes are defined for the absolute thresholds as well as for the relative thresholds. In the first indexes group, there is for example the number of days with heavy precipitation (rr ≥ 10 mm). In the second group, the indexes are defined with percentiles; the thresholds are defined for each series with the 1971-2000 period as reference. |
Dubuisson & Moisselin 2006 - A | |
World: During recent warm decades, some evidence exists that rainfall events in a number of countries have become more intense. Examples are known from the United States, Canada, Australia, Japan, South Africa, and Europe. In the United Kingdom an upward trend has occurred in the largest winter rainfall events [see references in the study]. |
Bibliographic review. | Goudie 2006 - A | |
Southern
Germany: • Significant decrease in the catchment precipitation in the summer half year, especially in North Württemberg and Lower Franconia; in Eastern Bavaria the decrease shows only a low level of significance; in Southern Bavaria a slight increase can be noted. • Increase, in most cases significant, in the catchment precipitation in the winter half year; the foothills of the Alps are an exception, where the slight increase is not statistically significant. • Regional clear increase in heavy precipitation by 30-35% in the winter half year; however, in summer only small changes. • Regional foci of heavy precipitation in winter can be found in the Black Forest, in the Northeast of Baden-Württemberg and in the Northern Bavarian Region • Winter half year more humid, summer half year drier In the winter half year, the precipitation-bearing Western weather fronts have increased in Southern Germany. |
Extensive and, as far as possible, homogeneous
data on precipitation behaviour are fundamental prerequisites for the
better understanding of the interaction of climate and water cycle.
For this purpose the long precipitation series on all available stations
in Southern Germany were interpolated with a geostatistical method to
yield grid point precipitation and daily catchment precipitation heights
were calculated. Statistical parameters for the daily values for the
catchment area in one month were then analysed as representative partial
samples. The series of the monthly values formed in this way were analysed
in detail in a time series analysis. Station time series were employed to examine heavy precipitation. [Framework: KLIWA Project] |
Hennegriff & al 2006 - A | |
World: There are no significant trends in the floods frequency or intensity: most of the observed precipitation increase concerns the 50-75mm/day range that are not leading to flood event most of the time. There are no proofs of a precipitation pattern increase that typically trigger floods (as >100 mm/day or > 200-400 mm for several consecutive days). |
Lins 2006 - E | ||
| Swiss
Pre Alps: In contrast to the temperature trends, precipitation totals (mean of 3 stations) apparently have no significant trends at all. |
The meteorological data used are the average values for three stations located in a triangle 10 km around the studied site and the Chateau d'Oex data, station located more than 40 km from the studied site. |
Perret & al. 2006 - A | |
North hemisphere / German Alps:
The precipitation distribution show a regional evolution with 0.5-1% increase per decade in the middle and high latitudes in the North hemisphere and 0.3% decrease in the continental subtropical regions. In South Germany and some Alpine regions, the spring and end of winter precipitation increased of 20 to 30%, while summer precipitation at the same time decreased of around 20%. |
Seiler 2006 - P* | ||
| Alps: The number of days with extraordinarily heavy snowfall was constant since 1970. |
Umweltdachverband 2006 - R* | ||
Switzerland: During the 20th century, winter precipitation increased from 10 to 30% in the Northern Alps and in the Western parts of the country. Swiss data series do not allow concluding systematic changes in the frequency of rare extreme meteorological events. However, it is important to keep in mind that a statistical proof could only be brought if very strong changes occurred. Thus it is not excluded that climate change already had an impact on the occurrence of extreme events. On the other hand, it has been noticed that intense meteorological events (which generally do not lead damages) underwent systematic changes, according to Swiss measure series. In autumn and winter (but not in summer), heavy precipitation became more frequent. |
Frei & Widmer 2007 - E | ||
| World:
The frequency of heavy precipitations events has increased over most land areas, consistent with warming and observed increase of atmospheric water vapour. Long-term trends from 1900 to 2005 have been observed in precipitation amount over many large regions. Significantly increased precipitations have been observed in northern Europe. Drying has been observed in the Mediterranean. Precipitation is highly variable spatially and temporally, and data are limited in some regions. |
IPCC 2007 - R (SP) | ||
Écrins massif: A significant increase of summer precipitations with intensity above or equal to 30 mm/day over the 1986-2000 period has been observed. |
Non-homogenized daily meteorological data (mean, minimal and maximal temperature and daily precipitation since 1961) provided by three meteorological stations located around the massif des Écrins: La Salette (1770 m a.s.l.), Monétier-les-Bains (1490 m) and Saint Christophe en Oisans (1570 m). |
Jomelli & al. 2007a - A | |
Écrins massif: Only St Christophe and Névache stations presented significant variations in intensity of precipitation occurring between 15/06 and 15/10 since 1961 but the frequency of these events increased at all the stations except Corps. A climatic signal is observed at the scale of the Écrins Massif characterized by a significant increase of extreme precipitation in summer. |
Meteorological data have been collected from 9 stations with different elevations and periods of observation located in the Massif des Ecrins to characterize climatic change in the massif as a whole. |
Jomelli & al. 2007b - A | |
| Switzerland: Annual precipitation increased by about 120 mm (8 %) during the 20th century. This significant increase is mainly due to the increase of average winter precipitation, which increased by 20-30 % in the northern and western Alps (Schmidli et al., 2002; Bader and Bantle, 2004; Begert et al., 2005). However, since the beginning of 21st century, a winter precipitation decrease can be observed in the North of the Alps . So, it is not possible any more to draw a clear trend as regards to the precipitation evolution since the beginning of the 20th century. On the other hand, the frequency of intense precipitation (30-day return period) increased almost everywhere in Switzerland since 1900 (Schmidli and Frei, 2005). In winter and fall, the increase is statistically significant for numerous stations located in the North of the main Alps range, where the frequency increased from 15 to 70 %. On the other hand, in spring and summer, as well as in the South, no significant change was highlighted. With the 0°C line rise observed the last 50 years, the snow amounts and the snowfalls frequency on the Plateau and in the PreAlps decreased since the 1960s. In a general manner, the number of days with snowfalls decreased. |
Bibliographic review | North & al. 2007 - R: OFEV | |
French Alps: The precipitation data reveal a strong annual variability but a weak decadal variability. The 5-year average shows similar temporal changes for the 3 stations. From these data, it can be seen that the decadal precipitation did not vary by more than ±10% over the 20th century. |
The precipitation variability observed at meteorological stations in valley locations (Besse en Oisans, Bourg Saint Maurice and Chamonix) has been investigated. |
Vincent & al. 2007a - A | |
Piedmont and Valle d'Aosta (North-western Italy): Even if the ensemble averages of precipitation variables do not show any significant trend, these can instead be found for individual station data. Overall, stations showing a significant positive trend are offset by others showing significant negative trends. No elevation-dependent pattern emerges from these results, as the stations with significant positive or negative precipitation trends are evenly spread in elevation. Even if no significant trend is associated with the longest duration of a dry spell in a year, this statistic shows extremely strong fluctuations, especially in recent years. Frequent episodes with very long dry spells are evident, particularly starting from 1989. Extension of the analysis to other statistics, which characterize the intra-annual temporal distribution of observed precipitation and the nature of precipitation events, indicates the absence of significant trends in all the variables considered. Precipitation is (negatively) correlated with NAO only in winter, while a positive phase of SCAN leads to increased precipitation all over the year. In general these results are consistent with the role of SCAN for precipitation in Italy discussed in Wibig (1999). The Euro-Atlantic blocking index has correlations that are similar to those of the negative phase of NAO: The index shows no significant correlation with precipitation, in contrast with the results reported in Quadrelli et al. (2001). The European blocking (EB) index shows, not surprisingly, a behaviour analogous to the SCAN index: It is associated with high precipitation in summer and fall and with low temperatures from winter to summer. |
Time series of daily cumulated precipitation, measured by a dense and uniformly distributed observational network (119 rain gauges) were analysed. This study has focused on the period 1952-2002. All available time series were checked for internal consistency and for the presence of outliers. Some stations provided valid data only for a fraction of the entire period of interest and some years are incomplete. Temporal interpolation techniques were used to fill these gaps and analyse only the measured data. “Ensemble averages” mean averages taken over the set of measurement stations. Monte-Carlo methods were extensively used to estimate sampling errors and to assess the significance of the results. The results provided by this method were compared with a standard Mann-Kendall test at the same significance level. The following statistics were defined, all averaged on a yearly or seasonal time scale: average precipitation, precipitation intensity (precipitation averaged only over rainy days), the average duration of dry periods and of rainy events in each year/season, the average cumulated precipitation in rainy events and the percentage of non-rainy days. Extremes were analysed by computing also the longest duration of dry spells in a period, the longest duration of rainy episodes and maxima of cumulated precipitation per event in each year. For each station, these statistics were standardized to unit variance and zero mean before further analysis. The authors computed the correlation of the seasonally-averaged precipitation and temperature time series with the NAO (North Atlantic Oscillation), SCAN (Scandinavia), EA (East Atlantic) and EAWR (East Atlantic/West Russia) teleconnection indices. The teleconnection patterns were all computed from NCEP reanalysis data in the period 1950-2000. Significance of correlations was determined using both a standard Student's t-test and a shuffling Monte-Carlo method, obtaining the same results in all cases. |
Ciccarelli & al. 2008 - A | |
Swiss Alps (Sion and Zermatt): Total annual precipitation between November in one year and October in the next (P 11–10) showed considerable year-to-year fluctuation. After several wet years in the 1860s–70s, precipitation at Sion from the 1880s to 1900s was generally below the long-term average of 571 mm, although 1895/96 was the wettest year in the series (the second wettest at Zermatt). Between the 1900s and 1950s, precipitation varied about a slightly rising trend, but with several exceptionally dry (1920/21, 1924/25) and wet years (1944/45) at Sion. The cool 1970s had both dry and wet years but with no trend through to the warm 1990s–2000s, which included the second wettest year in the record (1989/90) but with several years below average. After the wet years from the mid-1970s to 1981/82, P 11–10 for Zermatt declined, with the majority of annual values below the station average, including 1989/90. |
Long precipitation series are available from Sion for 1865–1977 and Zermatt for 1893–1922 at 1609 m and for 1926–2006 at 1632 m a.s.l. Homogenized monthly precipitation data from Meteo-Schweiz for Sion Aéroport now provide an extended series at one location. |
Collins 2008 - A | |
Alps: When trying to compare the temperature evolution with the precipitation evolution, only few correlations have been found. Indeed, the temperature in a specific point influences in a slightly manner the precipitation pattern in this point. Ultimately, temperature in a specific point might lead to the triggering of convective precipitation, but precipitations originate in a much larger scale and are rather determined by types of circulation, by bringing wet air from the Atlantic Ocean or the Mediterranean Sea. Thus it is very difficult to link a global increase of temperatures (and even a regional increase) to a possible evolution of precipitation pattern. |
Beniston 2007 - C1 | ||
French Alps: The increase of the frequency of heavy precipitation, which seems to have been observed in the Alps, is not very clear and rarely justified by using statistical tests. In France, no significant trend in data series of heavy precipitation has been observed for the last 40 years, whatever the timeframe considered. |
Bois 2007 - C1 | ||
|
Modeling |
Western
(Swiss) Alps: Winter precipitations would increase by 15%. With expected climate warming, the average predicted precipitations would not change, but summer precipitations should decrease, while winter precipitations would increase. Modelling of winter storms suggest a stronger frequency of southern flows from the Mediterranean and heavy storms, like 1999 Lothar storm (Beniston 2004). Also, periods of drought could be more frequent as well as periods of heavy rainfalls. |
Beniston 1995 et 2004 in Bravard 2006 - P | |
| Alps: The amounts of precipitation are influenced by the Northern Atlantic Oscillation. |
Beniston 1997 in Bravard 2006 - P | ||
| Europe:
Averaged over the model domain the mean precipitation increase is most evident for areas that already experience wet conditions in the CTRL, like the Alpine region, which shows a relative increase of 12%. However the limited sample size and the magnitude of the case-to-case variations militate against identifying statistically significant regional variations for this relative increase. The simulated warming has a significant impact upon the intensity distribution of the precipitation events. For light-intensity events the effect is marginal, and the frequency of rainy days (>0.1mm per day) remains almost unchanged. However the effect progressively increases with precipitation intensity, and is most pronounced for strong events. Occurrences exceeding 30mm per day are more frequent by more than 20% for the Alpine region. Indeed it is the change in the frequency of high-intensity events that is the major contributor to the simulated increase in the mean precipitation. The results suggest that the stipulated increase in the atmospheric moisture content has marginally affected the spatial extent of the simulated precipitation systems but resulted in a change of their intensity leading to substantial reductions in the return period of strong events. |
The regional climate model utilized is the hydrostatic mesoscale weather forecasting model developed at the German Weather Service, driven by observed and modified lateral boundary conditions and sea-surface temperature distributions. In a first step a control simulation (referred to as CTRL) is conducted of the present-day climate by driving the model at its lateral boundaries with the observed weather evolution (perfect boundary conditions). In the second step a sensitivity experiment is conducted with the initial and boundaryelds of the first realisation modified by an uniform temperature increase of 2K. Also, consonant with inference from observations and GCM experiments, the boundary condition for relative humidity is left unchanged and this results in a domain-averaged 15% increase of the atmospheric moisture content. Results will be presented of month-long simulations for an ensemble of five October months (1987, -88, -89, -90, -92), representative for the fall-time climatic conditions over Central Europe.
The response in precipitation intensity is assessed by considering the simulated daily rainfall totals at gridpoints grouped in sub-areas of the model domain. The frequency distributions for the ensemble of the CTRL integrations compare well with those derived from an objective analysis of observed daily precipitation. The slight tendency to overestimate the occurrence of moderate to high precipitation events is associated with the overall wet bias. |
Frei & al. 1998 - A | |
Italy - Eastern Dolomites: |
The study is based on climate projections of a general circulation model (GCM). GCM output is postprocessed with a statistical downscaling technique to derive local-scale climate change information from simulated atmospheric circulation patterns of the European–North Atlantic sector. |
Dehn & al 2000 - A | |
| Alps: Major discrepancies appear in the Ticino area (southern Switzerland) where the model strongly overestimates the mean precipitation. The same applies in the southwesternmost parts of the Alps and along the crest of the Apennines. Underestimations appear along the northern and south-eastern boundary of the Alps. The simulated change of summer precipitation shows a significant decrease by 20 to 50 percent in most parts of western central Europe. An even stronger decrease (50 to 100 %) is simulated along the Saone-Rhône valley in France. The strongest absolute decline (-7mm/day), however, appears over the western Alps (northwest of Milano) just where the result for the present-day climate shows the strongest positive bias. Increasing precipitation is simulated around the Adriatic Sea, the eastern parts of the Alps and parts of eastern central Europe. Again, the strongest relative change (>100 percent increase) appears over the eastern Po valley where the present-day result has the strongest (negative) bias. At many Alpine and northern Italian stations the absolute bias exceeds the simulated absolute value of the climatic change. This fact certainly limits the reliability of the climate change results in these areas. |
In this study statistical-dynamical downscaling is applied to two 30-year periods of a transient climate scenario simulation with a coupled ocean-atmosphere GCM. The first period represents the present-day climate (1971-2000) while the second period represents a possible largescale climate 100 years later (2071-2100). The downscaling was performed for the greater Alpine region. The study is restricted to the summer months, i.e., June, July, and August. The data used are the results from the coupled atmosphere-ocean modelling system ECHAM4/OPYC3 with ISC92a scenario. In order to assess a possible climate change, the results of two 30-year periods 1971-2000 and 2071-2100 were selected. The precipitation grid-based data (mesh size: 25x25 km2) were derived from the daily measurements of about 5000 rain gauge stations in southern Germany, Switzerland, Austria, south-eastern France, northern Italy, Slovenia, and Croatia. |
Heimann & Sept 2000 - A | |
| France: The ECLAT-2 programme predicted a minimum of precipitations in summer months (from -45% to +8%), and increased precipitations in winter, up 530% according to the models. The changes associated with an increase in global temperature are rendered more complex by interactions with the NAO shifts. |
In
the framework of the ECLAT-2 project (1998-2001),
downscaling techniques were applied to the Rhone basin (Noilhan et al.,
2000), using selected GCM ouputs in the basin for doubled C02 concentration
conditions. These studies explored the sensitivity of the production functions
of the hydrological model to anomalies in precipitations and temperatures
for selected sub-basins during the period 1981-1985. |
Noilhan & al., 2000 in Bravard 2006 - P | |
| World:
Current climate models simulate a climate change-induced increase in annual precipitation in high and mid-latitudes. Global climate models currently cannot simulate with accuracy short-duration, high-intensity, localized heavy rainfall, and a change in mean monthly rainfall may not be representative of a change in short-duration rainfall. |
IPCC 2001 - R | ||
World / Rhone watershed: At the [Rhone river] basin scale, the General Circulation Model (IPCC, 1996, 2002) projects that the expected climate warming will enhance the hydrological cycle, with higher precipitations in winter, higher rates of evaporation and decreased precipitations in summer and during the fall, and a proportion of liquid to solid relatively greater at high altitude. Two scenarios have been tested: - B2: average temperature would increase by 2-2.5°C in one century. - A2: average temperature would increase by 3-3.5°C. This model having been recognized to be unable to reproduce the characteristics of variables at the regional and short time scales, different projects have been launched in order to address this issue. France: According to GIEC models applied to France, with the B2 scenario (+ 2-2.5°C in one century), precipitations would increase in the winter, while they would be reduced by 5-25% in the summer. According to the A2 scenario (+ 3-3.5°C in one century), summer droughts would be more severe with a decrease of 20-35% in summer rainfall, associated with severe episodes. |
The assessment of climatic change has been traditionally based on general circulation models (GCM) which typically have a resolution of 2.5° latitude and 3.75° longitude. |
IPCC 1996, 2002 in Bravard 2006 - P | |
Mediterranean
region: The scenario illustrates the existence of a substantial change in the rainfall distribution over a relatively large subtropical region, the Mediterranean, in which the "increase in variance" overcomes the "reduction in the mean" [Meehl et al., 2000]. These results strongly illustrate the trends suggested due to global green-house gag warming. Both modeling [Hennessy et al., 1997], and observational studies [Brunetti et al., 1999], show that this reduction is associated with fewer rainy days. The latter is exp1ained by the increase in the frequency and persistence of sub-tropical anticyclones, particular1y over the Mediterranean. |
Various authors in Alpert & al. 2002 - A |
||
France: The ratio of solid precipitation over total precipitation decreases significantly over the Rhone basin (-21%), particularly for low and medium altitude watersheds, and the duration of the snow cover reduces. |
Results of ARPEGE for the 2054-2064 period for the 2*CO2 scenario. |
Etchevers et al. 2002 - A | |
Rhone river watershed: With a “2*CO2” scenario and according to various models, monthly anomaly of precipitation is generally positive during the winter months, with values ranging between 0 and 25%. Given the air temperature increase, the total precipitation increase is not leading to a snowfall increase. |
Etchevers & Martin 2002 - P | ||
Europe: The probability of occurrence of E2 over Europe from the control ensemble in boreal winter is approximately 2.5%. The probability of E2 (The dichotomous event En, defined to occur if the total seasonal precipitation at a specific location exceeds n standard deviations above the mean) at the time of CO2 doubling has increased to over 12% (associated with enhanced storm-track activity and “wetter” storms) for much of central and northern Europe. Alps: For the alpine region, the probability of occurrence of E2 from the control ensemble is 2-4%, and 6-12% from the greenhouse ensemble. The probability of occurrence of a very wet winter over the alpine region is estimated to increase by a factor of 3-5 over the next 50-100 years, due to man's effect on climate. |
Palmer & Räisänen 2002 - A | ||
Mountain
area: Projections of changes in the precipitation patterns in mountain are tenuous in most General Circulation Models because mountain topography is poorly resolved and, as a result, the controls of topography on precipitation are not adequately represented. It has also been recognized that there are superimposed effects of natural modes of climate variability such as El Nino/ENSO, NAO... ...can perturb mean precipitation patterns on time scales ranging from seasons to decades. Such mechanisms are not well predicted by climate models. |
Beniston 2003 - A | ||
Europe/World: Simulations consistently predict that summer precipitation will be reduced in many mid-latitude regions, whereas at higher latitudes there will be little change or possibly an increase. Although OAGCMs indicate an intensified global hydrological cycle in a warmer climate, evidence of changes in extreme precipitation at the regional scale remains unconvincing. The low spatial resolution of OAGCMs precludes a realistic simulation of regional circulation and therefore of extreme precipitation. Europe: Relative change in the mean five-day precipitation for July–September that exceeds the 99th percentiles in scenario A2 with respect to the control (present day): even when a reduction in total mean precipitation is simulated, the amounts of precipitation in the intensive events are much less reduced, and even increase in many places. The higher the percentile considered, the larger are the areas that show a positive change. A standard Mann–Whitney test on a series of events that exceed different thresholds indicates that there is a significant change at the 95% level for events above the 95th percentile, but the small sample size precludes a general, unequivocal detection of change for the 99th percentile (or higher). This, however, does not necessarily imply the absence of change. These changes are seen for a wide range of percentiles and for most European land points, with exceptions being mostly located on the Iberian Peninsula and over the Balkans. Similar analysis, averaging the precipitation data over several European river catchments: With few exceptions (involving rivers situated in a very dry environment), an increase in the amount of precipitation during extreme precipitation episodes is simulated in both scenarios (most prominent in A2). Using the combined information from both simulations, we find that CO2-induced warming can lead to a shift towards heavier intensive summertime precipitation over large parts of Europe; the warmer scenario (A2) gives the largest shift. This finding may be explained by the fact that the atmosphere will contain more water in a warmer climate (according to the Clausius-Clapeyron equation), which will provide further potential for latent-heat release during the build-up of low-pressure systems, thereby possibly both intensifying the systems and making more water available for precipitation. |
In the European Union project PRUDENCE, the high-resolution (50-km grid) regional climate model HIRHAM4 created by the anish Meteorological Institute has been applied to two of the emission scenarios, A2 and B2, drawn up by the intergovernmental Panel on Climate Change (IPCC). Three 30-year time-slice experiments were carried out for periods representing roughly the present (1961–90) and two future scenarios (2071–2100), respectively. The large-scale controlling conditions originated from transient climate-change simulations using the coupled ocean–atmosphere global climate model (OAGCM) ECHAM4/OPYC (300-km grid). |
Christensen & Christensen 2003 - A | |
Europe: The overall patterns of change are the same (although the RCM exhibits an enhanced drying) with a relatively large decrease over Central and Southern Europe and a general increase in the northernmost regions. But there are also marked differences on the regional scale. Note in particular the orographically induced additional increase along mountain slopes of Western Norway and the change in the geographical position and magnitude caused by the representation of the Alps This is accounted for mainly by the differences in model topography. Thus, the relatively large area with an increase in precipitation over Italy in the ECHAM4 simulation is reduced to a small region around the Po valley, likewise, along the east coast of the Iberian Peninsula. These kinds of resolution-dependent differences are seen in all seasons. The enhanced drying is in agreement with findings in other studies using RCMs with a European focus (Machenhauer et al., 1998; Jones et al., 1997; Rummukainen et al., 2001). In comparing the two experiments, it is also seen that the ECHAM4-driven run shows a tendency for a larger shift towards more intensive precipitation. This is in agreement with the HadAM3H-driven runs showing a larger reduction in mean precipitation. From the analysis so far, there is no guarantee that the spatial patterns of increase are temporally correlated; that is, the statistic is done for individual grid points. [The authors] have therefore carried out the same analysis after lumping the precipitation data over eight different European river catchments. For those of the rivers, which have their origin and a sufficiently large subcatchment within the Alps (the Rhine, Elbe, and Danube), we have further discriminated against high altitude, in that we only consider the areas which are located more than 400 m above sea level. This may seem as a somewhat arbitrary choice but is the result of a compromise between having enough grid points to sample from and still represent the upper catchment areas reasonably well. This way, we furthermore focus on areas like those causing the recent floodings in this region. To summarise the behaviour we show the relative change in average precipitation and in exceedence of the 95th and 99th percentiles for eight important and geographically different river systems: The Torne River in Northern Sweden, the Odra, the upper Rhine, the upper Danube, the upper Elbe, and the Rhône rivers representing Central Europe, plus the Ebro and Po rivers representing Southern European rivers. A running 3-month window has been applied in the analysis in order to have sufficient data points. [ECHAM boundaries and HadAM3H boundaries have been differenciated]. The seasonality of the relative change of average precipitation is similar in the two experiments. The two experiments have different seasonality in the relative change of high exceedences however. The average precipitation is generally decreasing in the summer period. But higher percentiles have increasingly more positive values resulting in some large increases of extremes, especially for the important central-European rivers. The ECHAM-driven experiments show rather large increases in late summer, but the HadAM3H-driven experiments do not share this feature; nevertheless, also this set of experiments has more positive values for the high intensities than for the mean in the summer. The ECHAM/OPYC B2 scenario, which is not shown here, generally exhibits the same signals as the corresponding A2 scenario, but with the expected smaller magnitude. |
In [this] approach, [the authors] have selected [...] the scenarios A2 and B2 in order to test the sensitivity of climate change to the degree of global warming. In addition, [they] have chosen to study the sensitivity of [the] results to the driving boundary conditions by conducting experiments using boundaries from two different global models. Two time slices were chosen to represent the current climate (1961–1990) and the future (2071–2100), respectively. [The GCM used were the ECHAM 4/OPYC and the HadAM3H]. The studies were carried out using a horizontal resolution of 0.44° corresponding to 50 km. The initial atmospheric and six-hourly updates of lateral boundary conditions were taken from the ECHAM4/OPYC and HadAM3H simulations, respectively. Sea surface temperatures and sea–ice conditions were updated daily by spatially interpolated fields from the same model simulations. Before either integration, the model was spun up for 2 years following the procedure proposed by Christensen (1999) to ensure a well-balanced initial state.
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Christensen & Christensen 2004 - A | |
Thur and upper Ticino river basins (Swiss Alps): The mean annual P from the SD scenarios was found to increase by 37 mm in the Thur basin and to decrease by 48 mm in the Ticino basin. In relative terms, these changes were small for both basins (less than 3%). On the other hand, the scenario range was quite large and reflected a high degree of uncertainty in the projections. For the Thur basin the annual changes in P ranged from -72 mm (-5%) to +160 mm (+11%), whereas for the Ticino basin the spread was from -205 mm (-11 |