Abstract
Abstract. The Paris Agreement sets a long-term temperature goal to hold global warming to well below 2.0 ∘C and strives to limit it to 1.5 ∘C above preindustrial levels. Droughts with either intense severity or a long persistence could both lead to substantial impacts such as infrastructure failure and ecosystem vulnerability, and they are projected to occur more frequently and trigger intensified socioeconomic consequences with global warming. However, existing assessments targeting global droughts under 1.5 and 2.0 ∘C warming levels usually neglect the multifaceted nature of droughts and might underestimate potential risks. This study, within a bivariate framework, quantifies the change in global drought conditions and corresponding socioeconomic exposures for additional 1.5 and 2.0 ∘C warming trajectories. The drought characteristics are identified using the Standardized Precipitation Evapotranspiration Index (SPEI) combined with the run theory, with the climate scenarios projected by 13 Coupled Model Inter-comparison Project Phase 5 (CMIP5) global climate models (GCMs) under three representative concentration pathways (RCP 2.6, RCP4.5 and RCP8.5). The copula functions and the most likely realization are incorporated to model the joint distribution of drought severity and duration, and changes in the bivariate return period with global warming are evaluated. Finally, the drought exposures of populations and regional gross domestic product (GDP) under different shared socioeconomic pathways (SSPs) are investigated globally. The results show that within the bivariate framework, the historical 50-year droughts may double across 58 % of global landmasses in a 1.5 ∘C warmer world, while when the warming climbs up to 2.0 ∘C, an additional 9 % of world landmasses would be exposed to such catastrophic drought deteriorations. More than 75 (73) countries' populations (GDP) will be completely affected by increasing drought risks under the 1.5 ∘C warming, while an extra 0.5 ∘C warming will further lead to an additional 17 countries suffering from a nearly unbearable situation. Our results demonstrate that limiting global warming to 1.5 ∘C, compared with 2 ∘C warming, can perceptibly mitigate the drought impacts over major regions of the world.
Highlights
Climate warming mainly due to greenhouse gas emissions has altered the global hydrological cycle and resulted in more frequent and persistent natural hazards such as droughts, which have imposed considerable economic, societal, and environmental challenges across the globe (Handmer et al, 2012; Chang et al, 2016; EM-DAT, 2018)
We find that mean Standardized Precipitation Evapotranspiration Index (SPEI)-3 decreases at the global scale, except in very limited regions in high-latitude areas (e.g., Siberia in Russia), where it exhibits a slight increase
Motivated by the 2015 Paris Agreement proposal, we quantify the changes in global drought bivariate magnitudes and socioeconomic consequences in the 1.5 and 2.0 ◦C warmer worlds, with climate projected by the multi-model ensemble under three representative concentration pathways (RCP2.6, RCP4.5, and RCP8.5)
Summary
Climate warming mainly due to greenhouse gas emissions has altered the global hydrological cycle and resulted in more frequent and persistent natural hazards such as droughts, which have imposed considerable economic, societal, and environmental challenges across the globe (Handmer et al, 2012; Chang et al, 2016; EM-DAT, 2018). One way is to employ a set of ensemble simulations produced by a single coupled climate model (e.g., Community Earth System Model, CESM) which is designed to perform the impact assessments at near-equilibrium scenarios of 1.5 or 2 ◦C additional warming (Sanderson et al, 2017; Lehner et al, 2017) This single model type cannot reflect the structural uncertainty of climate models, which is important in impact assessments, and raises doubts about the robustness of such drought condition assessments (Liu et al, 2018a). Su et al (2018) used 13 CMIP5 models based on RCP2.6 and RCP4.5 to compare the drought conditions for two warming targets over China and reported that tremendous losses will emerge even under the ambitious 1.5 ◦C warming target
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