Super droughts over East Asia since 1960 under the impacts of global warming and decadal variability

Abstract

In the last decade, a sequence of once-in-50 year or even once-in-100 year high-impact drought events have hit East Asia. By defining a super drought with the Standardized Precipitation Evaporation Index for the time scales of 3, 6, 12 and 24 months all below −1.5, this study aims to examine the changes in super droughts and the underlying mechanism over East Asia in the past 60 years, putting the recent high-impact droughts in the context. Super droughts in the last 10 years over East Asia have been the most expansive, with two hotspots located in the Transitional Climate Zone (TCZ) and the Southeast Asian region (SEA) regions, together accounting for 2/3 of the total. The seasonal distribution characterizes the largest contribution from summer followed by autumn and then spring and winter. Super droughts over TCZ peak in the recent two decades, which are primarily driven by the increase in potential evaporation (PET) contributing 41 and 80% in the first and second 10 years, respectively. It turns out that global warming signal can explain more than 90% of this PET increase. Over SEA, the recent decade and the period around 1990 saw the most widespread super droughts that were not spatially uniformly distributed but clustered in three subregions. Different from TCZ, the precipitation rather than PET is the most influential in governing super droughts over SEA. Out of the total variability in precipitation, about half of the super droughts in the recent decade is caused by decadal variability, while the trend mode has negligible influence.