Global changes in drought conditions under different levels of warming

Abstract

Higher evaporative demands and more frequent and persistent dry spells associated with rising temperatures suggest that drought conditions could worsen in many regions of the world. Understanding and quantifying drought occurrence and severity across the globe for alternative mitigation targets is therefore imperative to support the stringent mitigation and adaptation goals stipulated in the Paris Agreement. In this study, we assess how drought conditions may develop across the globe for 1.5, 2, and 3°C warming compared to pre-industrial temperatures using an ensemble of high-resolution global climate simulations based on the Representative Concentration Pathway (RCP) 8.5. We analyse drought duration and magnitude through the Standardized Precipitation Evapotranspiration Index for 12-monthly rainfall accumulation (SPEI-12) and calculate changes in drought frequency between 30-year periods centered on the years when the different warming levels are reached and for the baseline (1976-2005) period. Results show that 2/3 of global population will experience a progressive increase in drought conditions with warming. For drying areas, drought duration are projected to rise at rapidly increasing rates with warming, averaged globally from 2.2 month/°C below 1.5°C to 10 month/°C when approaching 3°C. Drought magnitudes could double for 31% of global land mass under stringent mitigation. If contemporary warming rates continue, water supply-demand deficits could become five-fold in size for most of Africa, Australia, southern Europe, southern and central states of the US, Central America, the Caribbean, north-west China and parts of Southern America. In approximately 20% of the global land surface, drought magnitude will halve with warming to 1.5°C and higher levels, mainly most land areas north of latitude 55°N, but also parts of South-America, Eastern and South-eastern Asia. A progressive and significant increase in frequency of droughts is projected with warming in the Mediterranean basin, most of Africa, West and Southern Asia, Central America and Oceania, where droughts are projected to happen 5 to 10 times more frequent even under ambitious mitigation targets and current 100 year events could occur every 2 to 5 years under 3°C of warming.