A multi-model and multi-index evaluation of drought characteristics in the 21st century

Abstract

Drought is a natural hazard that can have severe and long-lasting impacts on natural and human systems. Although increases in global greenhouse forcing are expected to change the characteristics and impacts of drought in the 21st century, there remains persistent uncertainty about how changes in temperature, precipitation and soil moisture will interact to shape the magnitude – and in some cases direction – of drought in different areas of the globe. Using data from 15 global climate models archived in the Coupled Model Intercomparison Project (CMIP5), we assess the likelihood of changes in the spatial extent, duration and number of occurrences of four drought indices: the Standardized Precipitation Index (SPI), the Standardized Runoff Index (SRI), the Standardized Precipitation–Evapotranspiration Index (SPEI) and the Supply–Demand Drought Index (SDDI). We compare these characteristics in two future periods (2010–2054 and 2055–2099) of the Representative Concentration Pathway 8.5 (RCP8.5). We find increases from the baseline period (1961–2005) in the spatial extent, duration and occurrence of “exceptional” drought in subtropical and tropical regions, with many regions showing an increase in both the occurrence and duration. There is strong agreement on the sign of these changes among the individual climate models, although some regions do exhibit substantial uncertainty in the magnitude of change. The changes in SPEI and SDDI characteristics are stronger than the changes in SPI and SRI due to the greater influence of temperature changes in the SPEI and SDDI indices. In particular, we see a robust permanent emergence of the spatial extent of SDDI from the baseline variability in West, East and Saharan Africa as early as 2020 and by 2080 in several other subtropical and tropical regions. The increasing likelihood of exceptional drought identified in our results suggests increasing risk of drought-related stresses for natural and human systems should greenhouse gas concentrations continue along their current trajectory.