Data-based hydrometeorological drought indicators and appropriate temporal aggregation scales for studying drought impacts

Recent consecutive dry summers in North Western Europe caused significant impacts across ecosystems and socio-economic sectors. Climate change is expected to increase the frequency and severity of drought and its impacts. To mitigate drought impacts in the future, it is crucial to improve our understanding on the effects of climate change on drought and its impacts.

A range of meteorological and hydrological drought indicators exists to quantify droughts. Depending on the drought impact of interest, different indicators aggregated over different timeframes (temporal aggregation scales) may be relevant. However, in climate change impact assessments, indicators currently are often used without assessing their relevance for the impact of interest. As a result, it often remains unclear which indicator and associated temporal aggregation scale is most appropriate for a given drought impact in a particular region.

We apply a bottom-up, data-driven approach to determine which hydrometeorological drought indicators are relevant and to identify their appropriate temporal aggregation scales for different drought impacts in the Dutch-German border region. Starting with drought impacts, such as agricultural yield loss, we derive hydrometeorological indicators and their temporal aggregation scales. For example, we analyse the correlation between groundwater table depths with varying temporal aggregation scales and crop yield loss simulated with the WaterVision Agriculture tool. Among the tested temporal aggregation scales (1 to 12 months), a five-month aggregation of groundwater table depth shows the highest correlation with agricultural yield loss. This shows that the groundwater table depth aggregated over the final five months of the cropping season is an important hydrological drought indicator for agricultural yield loss in the Dutch-German border region. Next steps include extending the analysis to other drought impacts and linking hydrological and meteorological indicators.

This analysis improves understanding on the relevance of various hydrometeorological indicators and associated temporal scales for different drought impacts and helps in assessing the effects of climate change on drought impacts in the future.