COST-733 WG4 The EU-WATCH project and links between WB4 and COST-733 Christel Prudhomme

WATer and global CHange (WATCH) WATCH Overview

WP4 : extremes scales of hydrological events WP4.1 Detection and attribution of extremes in the 20th century –historical droughts and large-scale floods in the 20th century –analysis and characterisation of those extremes WP4.2 Indices and tools to detect extremes and to assess uncertainty propagation –development of indices and tools to detect hydrological extremes –assess the uncertainty in the predicted extremes. WP4.3 Likely frequency, severity and scale of future hydrological extremes (21st century) –analysis of drought and large-scale floods based on the global and regional scenarios for the 21st century (WB3) –comparison with the simulations for the 20th century. WATCH WB4

Task ‘ Investigate processes and phenomena of major floods in 20th century’ Task ‘Spatial and temporal scales and severity of floods in 20th century Task ‘Large-scale climate drivers and drought and flood patterns –Flood catalogue –Antecedent conditions: e.g. soil moisture, rainfall; weather types –Are GCMs able to reproduce flood-generating rainfall patterns? –Are large floods in Europe linked to specific weather types –Are flood-generating weather types well reproduced by GCMs? WATCH WB4

Understanding large scale antecedent conditions Weather Types/ Classifications from COST –A priori, all classifications At present only for Europe: D00 For each large flood events –Frequency of weather type : preceding day(s) – “ : preceding weeks –Frequency anomaly (i.e. is situation exceptional?) –Blocking situation – blocking catalogue? –Systematic occurrence of some WT ? –Synoptic situation (from ERA-40?) Analysis of WT a-priory linked to large floods, but that did not trigger extreme events: How often? Why?

Flood Catalogue (Polish Academy of Science) Date DurationSpatial extent River/basinCharacteristicsSource 1959 December 2 Dam break flood - hours France(Malpasset dam, Reyran river valley Intense- and long lasting precipitatio n led to dam break and flood Legrand P., Les grandes catastrophes (4 tomes), Famot / Francois Beauval, Paris, June 15 HungaryDanube at Budapest Rainfall flood Word Catalogue of Maximum Observed Floods. Roche, M and Rodier, J. A IAHS-ASIH Publications 284 in the IAHS Series of Proceedings and Reports: July daysItaly – Central Alps Adda basin Heavy rain and rapid melting in alpine glaciers River Flood Disasters ICSU SC/IDNDR Workshop Koblenz, Germany 1996

Reproduction of antecedent conditions by GCMs Using Weather Types/ Classifications codes from COST –In priority for classifications showing good links with large floods Generate classifications from GCM runs of 20 th century Evaluate results against classifications from re- analysis/CRU –Frequency of Weather Type (monthly/seasonal/annual) –In particular, WT linked to large floods –Frequency of Blocking situation –Feed back systematic errors to WG1 (20 th century GCM simulation)

Area of interest outside Europe Application of classifications to future projections from GCM –Changes in frequency of WT –Potential implication for change of frequency in large floods After 18 th month from now

Advise on … …Best reference set: ERA-40? – but known deficiencies, e.g. rainfall …CRU climatology, but not all atmospheric variables? …What else?

Thank you