Regional hydrological drought in north-western Europe: linking a new Regional Drought Area Index with weather types

摘要

Links between severe hydrological droughts and weather types (WTs) were explored to improve the understanding onhydroclimatological processes involved in the development of regional hydrological drought in north-western Europe. A newnRegional Drought Area Index (RDAI) was developed, using daily streamflow, to represent the drought-affected area. DailnRDAI series (1964–2001) were created for two regions with homogeneous drought behaviour in Denmark and four regionnin Great Britain. An objective version of the Hess–Brezowsky Grosswetterlagen yielding 29 WTs was used. Regional droughncharacteristics, including duration and frequency, were found to vary considerably between regions. However, in 1976 ann1996, all regions experienced severe events, and these years were found to be the most severe drought years across the studnregion as a whole. The hydrological response time (i.e. the time over which WTs influence drought development) was founnto vary markedly (45–210 days) between regions according to basin storage properties. WT-frequency anomalies (FAs) befornand during the onset of the five most severe droughts were identified for each region. The dominant drought-yielding WTnchanged between regions and between events within each region. High-pressure systems centred over the respective regionwere most frequently associated with droughts as well as WTs with a northern (N, NE or NW) or a southern (S, SE or SWnairflow over the Danish and British regions. Five of the six WTs associated with drought for all regions represented a northernhigh-pressure system (i.e. over Great Britain, Fennoscandia or the Norwegian Sea). This article demonstrates (1) hydrologicanresponse time to be fundamental in moderating drought response to mesoscale climatic drivers and (2) severe hydrologicandroughts may be caused by a complex set of hydroclimatological processes that vary between regions and events. Copyrighn 2010 John Wiley & Sons, Ltd.