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 in 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 fifth phase of the Coupled Model Intercomparison Project (CMIP5), we assess the likelihood of changes in the frequency and severity 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 drought characteristics in two future periods (2010-2054 and 2055-2099) of the Representative Concentration Pathway 8.5 (RCP8.5). We find increases in the frequency, 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, several subtropical and tropical regions permanently emerge out of the baseline SPEI and SDDI drought frequency before 2080, including as early as 2020 over West Africa. The increasing likelihood of exceptional drought identified in our results suggests increasing risk of drought-related stresses for natural and human systems in the coming century should greenhouse gas concentrations continue along their current trajectory.
