Climate change impacts on NATURAL SYSTEMS AND PATTERNS 2.1 SOIL HUMIDITY / SURFACE WATER RUNOFF |
Type of knowledge |
Results and interpretation |
Observation and analysis methods
|
References |
Reconstructions |
European Alps: Starkel (1966) affirms that the melting and disappearance of frozen ground could lead to deeper water tables and to changes in water circulation. In particular, it can be hypothesised that, under permafrost conditions, groundwater recharge was not possible, while, after permafrost disappearance, groundwater recharge occurred and reached high values as a consequence of the rainfall and snowmelt increase that occurred during the improvement of climatic conditions following the last glaciations. |
Starkel 1966 in Bertolini & al 2004 - A | |
|
Observations |
Swiss Alps: The effect of precipitation increase (especially since 1978) during the mild winters (since 1988) on often unfrozen and with low snow cover grounds, at altitude between 1000m and 1500m a.s.l contribute to an important modification of the hydrological cycle in Eastern Switzerland. With the freezing/defreezing cycles increase during winter, the efficacy infiltration increased strongly during the period between November and March and lead to an early saturation of the flysch are, with limited permeability during spring. The precipitation and minimum temperature increase during winter is an aggrieving factor, with a direct effect on the water table level on surface and the water content of the unconsolidated materials in the Pre Alpine slopes under 1500 m a.s.l. |
Lateltin & al. 1997 - R: PNR31 | |
| World: Runoff tends to increase where precipitation has increased and decrease where it has fallen over the past few years. |
IPCC 2001- R (WG2) | ||
Switzerland: Given that the evaporation trend is almost identical to the precipitation trend (increase of 99 mm over hundred years), discharge remained almost constant over the last hundred years. |
Bibliographic review | North & al. 2007 - R: OFEV | |
|
Modeling |
World: In much of mid-latitude Europe, annual runoff would decrease or increase by about 10% by the 2050s, but the change resulting from climate may be smaller than “natural” multidecadal variability in runoff. |
IPCC 2001- R (WG2) | |
Europe: The evolution of the surface hydrological cycle under the influence of climate change has also been analysed by Douville et al. (2002). They concluded that the earlier snow cover melting should lead to an earlier runoff spring peak in Europe. The soil humidity would be increased in winter, particularly in Northern Europe, because of the precipitation increase and the earlier snow cover melting. In contrary, during summer the soil humidity should decrease, in relation with the evaporation increase, notably in spring, and with the summer precipitation decrease. Thus, climate change would potentially strengthen the seasonal cycle of soil humidity. |
Douville & al 2002 dans Planton & al 2005 - A | ||
Thur and upper Ticino river basins (Swiss Alps): ET was found to increase significantly in all experiments and for both regions. The 17-scenario mean showed an increase in the annual ET rate of about 16% relative to the control runs. The wetness index ET/PET showed significantly lower values in the projection time slice than in the control run. This is particular true for the summer period (JJA). Like the future evolution of ET/PET, the projections of soil water content (SWC) indicated decreasing values for both basins over most of the year, in particular during the vegetation period. The relative reduction in SWC was 7.2% (Thur basin) and 7.7% (Ticino basin) on a yearly average, and 9.7% (Thur basin) and 16.2% (Ticino basin) when averaged over the vegetation period from April to August. With respect to the wetness-index ET/PET and soil moisture, smallest changes were projected when using the SDT_P15 climate scenarios to drive the hydrological simulation. In this case, the uniform all season increase in P (+15%) almost compensates the potential T-induced decrease in ET/PET and SWC. |
Possible future changes in the natural water budget relative to the 1981-2000 (Thur) and 1991-2000 (Ticino) baselines were investigated by driving the distributed catchment model WaSiM-ETH with a set of 23 regional climate scenarios for monthly mean temperature (T) and precipitation (P). The scenarios referred to 2081-2100 and were constructed by applying a statistical-downscaling technique to outputs from 7 global climate models. |
Jasper & al. 2004 - A | |
Swiss Alps: A significant part of the discharge reduction is due to the predicted increase of evapotranspiration. For the currently glacierized catchments, this increase is partly a consequence of the significant glacier retreat, which results in an increase of the ice-free portion of the catchment where evaporation is subtracted from precipitation. Additionally, the substantial temperature increase throughout the seasons enforces the total evapotranspiration on ice-free areas; accordingly, all catchments show a strong increase of total evapotranspiration. This increase is expected to be less important in summers than in winters: even if there is a pronounced temperature increase in summer, summer evapotranspiration will be limited due to reduced precipitation. |
The climate-change scenarios analysed are the result of 19 regional climate model runs obtained for the period 2070-2099 based on two different greenhouse-gas emission scenarios and on three different coupled atmosphere-ocean general circulation models. The hydrological response of 11 mountainous catchments in the Swiss Alps to the climate scenarios is simulated through a conceptual reservoir-based precipitation-runoff transformation model. Actual evapotranspiration is estimated as a function of the potential evapotranspiration (PET) and the filling rate of the slow component reservoir. The PET data are derived from the monthly PET series estimated by New et al. (2000) for the 1961-1990 control period. |
Horton & al. 2006 - A | |
Alps: The comparison between runoff for the 1961-1990 period and potential runoff for the 2071-2100 period shows a strong increase of winter and spring runoff (and a consecutive increased flood risk) and a strong decrease of summer and fall runoff (and a consecutive larger drought risk). |
Beniston 2007 - C | ||
|
Hypothesis |
Europe: According to Petit (2001), "the Southern and Arctic Europe are more vulnerable than the rest of Europe. Particularly in summer, the runoff, the available water and the soil moisture will decrease in the Southern Europe, increasing its current drought vulnerability." |
ONERC 2005 - R | |
Alps / South Germany: One can expect a decrease of the underground water volumes because of drier and drier summers and of increasing evaporation. |
Seiler 2006 - P* |
Legend of bibliographical
references:
- * : study taken into account in WP7.
- A : Article (Peer reviewed publication)
- C : Comment
- E : Scientific study (unpublished)
- P : Proceedings
- R : Report
- Re : Experience Feedback
- T : Thesis
- W : Website