Recent trends in historical drought

Studies on past trends in drought indices and, in particular, those of hydrological drought have revealed complex patterns of variability and provided some emerging signals that could facilitate early detection of potential future changes in drought hazard. This chapter reviews studies from European projects that span a range of countries and scales, illustrating the many methodological aspects that influence trend assessments: data and catchment selection criteria, considered season, selected time period, the index analysed, and the measure used to quantify change. Most studies find an increase in drought severity in the south and east of Europe and highly seasonal differences in other regions, but readily available hydrometric records for continental‐scale analyses are sparse, particularly in regions of Europe with strong meteorological drying trends. This calls for improved efforts to collate the continental‐scale data needed to understand changes in drought, a phenomenon that is fundamentally large‐scale in nature. Furthermore, decadal variability affects the interpretation of trends, underlining the need to better understand the drivers of long‐term variability in hydrological drought across Europe.