Population exposed to drought under the 1.5 °C and 2.0 °C warming in the Indus River Basin

Based on multiple global climate models (GCMs), the Standardized Precipitation Evapotranspiration Index (SPED and Intensity-Area-Duration (TAD) method were used to identify drought events of the Indus River Basin (IRB) in the reference period (1986-2005) and under 1.5 degrees C (2020-2039 in RCP2.6) and 2.0 degrees C (2040-2059 in RCP4.5) global warming scenarios. Then, the population exposure was assessed by combining drought events with a projected dynamic population amount from five Shared Socioeconomic Pathways (SSPs), in which describe future of societal development considering the effects of climate change and climate policies. Research results show that both precipitation and evapotranspiration are projected to increase with global warming. Due to a higher increase in evapotranspiration than in precipitation, frequency, intensity, and areal coverage of drought events in the IRB are expected to increase under the 1.5 degrees C and 2.0 degrees C warming scenarios relative to the 1986-2005 reference period. In particular, frequency and areal coverage of extreme severe droughts will increase significantly. With aggravation of droughts across the IRB, annual population exposure will increase considerably from 43.2 million in 1986-2005 to approximately 114.4 million based on SSP1 (a sustainable world) under the 1.5 degrees C global warming scenario and will reach 163.1 million based on SSP3 (a strongly fragmented world) under the 2.0 degrees C scenario. Compared with the 2.0 degrees C level, maintaining the increase in global average temperature below the 1.5 degrees C limit can reduce the population exposed to drought by approximately 1.4-fold.