Compound droughts have become more widespread globally

Abstract. Compound droughts, in which meteorological, hydrological, and agricultural drought occur simultaneously, have a more substantial impact on ecological and socio-economic systems than any drought type alone. Yet, the global patterns – and particularly the multi-decadal trends – of these co-occurring droughts remain poorly understood. We analyse the global co-occurrence of meteorological, agricultural, and hydrological droughts from 1961 to 2020 using run theory and empirical drought indices from three global hydrological models (GHMs), each forced with three different meteorological forcing datasets. Our results indicate that compound droughts and their characteristics show distinct spatial patterns, varying across different hydrological regions. The findings suggest that compound droughts have become more widespread globally, particularly in the hydrological regions (i.e., hydrobelts) near the equator and in the southernmost regions, where the number of days under compound drought has increased rapidly over the past 60 years. Our results also show that compound drought behaviour in the boreal hydrobelt significantly differs from all other hydrobelts, showing a general wetting trend and no increase in compound droughts. We also, however, find a high uncertainty in the ensemble, highlighting a need to global hydrological modelling aimed toward droughts specifically. The results provide valuable global insights into complex phenomena of compound droughts, helping in drought preparedness actions and planning.