Trends and Drivers of European-Scale Drought

Abstract:

Drought is a costly and widespread natural hazard, with the characteristics and occurrence of drought expected to change under the more intense hydrological cycle that is expected as a result of climate change. However, there is much uncertainty as to whether changes in drought occurrence have already taken place, with contrasting results from different studies, in part due to the use of different drought indices. Improved understanding of present day variation, and the drivers of such variation, are needed to better understand how future changes in climate may influence drought. Here, time series variation (including trends) is analysed for two widely-used drought indices (the Standardised Precipitation Index and Standardised Precipitation-Evaporation Index) for the entire European continent for the period 1958 onwards. By analysing precipitation-driven (SPI) and meteorological water balance-driven (SPEI) drought this analysis will be able to provide information on water deficits in both the precipitation-dominated north, and in the south (where evaporation is more important). The SPI and SPEI can be examined at a range of timescales, typically from 1 to 24 months, thus providing a comprehensive range of information about the presence and propagation of drought through land surface hydrological systems. In addition to analysis of time series variation, climate mechanisms associated with drought occurrence are investigated, thus providing information on the mechanisms driving variation in drought occurrence. Results indicate that recent time series variation is the result of both cyclical and directional drivers, and that to be better understood, European-scale drought needs to be considered within the context of a complex series of time-varying interactions between different modes of large-scale variation in the ocean-atmosphere system.