Analysis - tempests

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STORM INTENSITY

Type of knowledge	Results and interpretation	Observation and analysis methods	References
Reconstructions	France: A study based on the use of data of pressure for the calculation of the geostrophic wind (Generoso, on 2000) concerning the period 1950-1999 showed that the method allowed finding 95% of storms and the totality of the strong storms. It also reveals that the number and the intensity of storms did not evolve much at the end of the XXth century and that they reached the level which was theirs in the beginning of the period. This is also confirmed by German and Scandinavians studies (Planton and Bessemoulin, on 2000).	For the study of the historic storms, it is possible to use data of pressure and to divert a windspeed from it by using the geostrophic hypothesis (balance between strength of pressure and strength of Coriolis; we speak then of "geostrophic wind").	Bessemoulin 2002 - E
Observations	France: It seems to have no statistically significant indications showing a storm frequency or intensity increase.		André & al. 2000 - A
	North Atlantic: Changes in storminess over the northeast Atlantic have been analyzed and show that although storminess has increased in recent decades, storm intensities are no higher than they were early in the 20th century.		IPCC 2001 - R
	France: By identifying the periods when at least 5% of a constant number of French stations monitored a daily maximal wind superior to 100 kph, Dreveton ( 2002 ) was able to select 734 episodes of strong wind over the period 1950-1999, representing 14,7 event per year on average. The use of a 20% threshold of stations allowed to isolate 71 strong storms over this period, representing 1,4 events per year. The number of episodes of wind presents a strong interannual variability (7 in 1968, 26 in 1962), as well as that for the strong storms (0 in 1989, 1993 and 1998, 5 in 1965), but the study does not highight any significant trend over the last 50 years. During Lothar and Martin (in December 1999), one identified, from the return period of the extreme values of wind calculated for the synoptic stations, three zones of secular winds or more: - A perimeter including Strasbourg, Colmar, Mulhouse, Orléans, Rouen, Reims, Nancy, Strasbourg, the majority of the values of which exceeded sometimes widely the 150 years values; - The foothill of the Pyrenees ; - The Atlantic Coast from Biscarosse to the Vendée.	Bibliographic review	Bessemoulin 2002 - E
	Switzerland: During the 20th century, three secular storms were recorded in 33 years: in February 1967, February 1990 and December 1999. However, these events are too unusual to allow a detection of a long-term statistical trend.		OcCC 2003 - R
Modeling	Atlantic: The Atlantic cyclogenese and depression tracks intensification signal provided by the models are on the edge of statistical significance.		André & al. 2000 - A
Hypothesis	France: Although expert advices are not identical concerning the evolution of extreme phenomena as storms, cyclones or thunderstorms, the probability of an increase and an aggravation of these phenomena is not excluded. Wetter winter and stronger tempest would lead to greater humidity.		ONERC 2004 - R
Hypothesis	South Germany / North Alps: Until the end of the century, one should expect hydrological cycle intensification, with a following extreme meteorological intensification: storms, tornadoes, droughts, extreme precipitations…		Seiler 2006 - P*

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STORM FREQUENCY

Type of knowledge	Results and interpretation	Observation and analysis methods	References
Reconstructions	France: A study based on the use of data of pressure for the calculation of the geostrophic wind (Generoso, on 2000) concerning the period 1950-1999 showed that the method allowed finding 95% of storms and the totality of the strong storms. It also reveals that the number and the intensity of storms did not evolve much at the end of the XXth century and that they reached the level which was theirs in the beginning of the period. This is also confirmed by German and Scandinavians studies (Planton and Bessemoulin, on 2000).	For the study of the historic storms, it is possible to use data of pressure and to divert a windspeed from it by using the geostrophic hypothesis (balance between strength of pressure and strength of Coriolis; we speak then of "geostrophic wind").	Bessemoulin 2002 - E
Reconstructions	Swiss: The damaging storms reconstitutions during the last 500 years in the Swiss plateau show a mean return period of 15 years. But important variations have been observed: no severe tempest occurred between 1562 and 1605 and en even longer pause occurred between 1787 and 1841. Nevertheless, each century experienced violent tempests and at least three have been observed during the 20th century (02/1967, 02/1990, 12/1999).	Historical documents analysis	Paul 2002 - A
Observations	France: It seems to have no statistically significant indications showing a storm frequency or intensity increase.		André & al. 2000 - A
Observations	France: By identifying the periods when at least 5% of a constant number of French stations monitored a daily maximal wind superior to 100 kph, Dreveton ( 2002 ) was able to select 734 episodes of strong wind over the period 1950-1999, representing 14,7 event per year on average. The use of a 20% threshold of stations allowed to isolate 71 strong storms over this period, representing 1,4 events per year. The number of episodes of wind presents a strong interannual variability (7 in 1968, 26 in 1962), as well as that for the strong storms (0 in 1989, 1993 and 1998, 5 in 1965), but the study does not highight any significant trend over the last 50 years.	Bibliographic review	Bessemoulin 2002 - E
Modeling	Europe: Modelling of winter storms suggest a stronger frequency of southern flows from the Mediterranean and heavy storms, like 1999 Lothar storm (Beniston 2004).		Bravard 2006 - P
Hypothesis	Switzerland: Nothing can be predicted about tempests or hail because the climate change impacts on this kind of events is unknown at the moment.		Frei & Widmer 2007 - E

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

Experiences feed-back	Objectives	Learnings	References

Recommendations	Remarks	Object	References