Impacts of reductions in non-methane short-lived climate forcers on future droughts

Droughts, prolonged periods of deficient precipitation and heightened evapotranspiration, pose severe threats to water resources, ecosystems, and socioeconomic well-being worldwide. While previous research has established that the continuous growth of greenhouse gas (GHG) emissions is a primary driver of global warming and the associated intensification of the hydrological cycle, the role of non-methane near-term climate forcers (NTCFs), including anthropogenic aerosols, in modulating drought risk remains less clearly understood. In particular, the complex interplay between aerosol-induced radiative cooling and greenhouse warming can produce non-linear drought responses at regional scales, notably in arid and semi-arid regions.

In this study, we employ seven Earth System Models (ESMs) participating in the Phase 6 of the Coupled Model Intercomparison Project (CMIP6) to investigate the specific contributions of NTCFs emission reduction to the evolution of drought characteristics (i.e., frequency, duration, and severity) under the SSP3-7.0 scenario. Droughts are identified by using the Standardized Precipitation Evapotranspiration Index (SPEI) at multiple timescales (3, 6, and 12 months). 

Results reveal considerable spatial heterogeneity in the responses of drought metrics. Reductions in NTCFs generally lead to cooler temperatures and, in many tropical and mid-latitude regions, enhanced precipitation. For parts of southern Africa and South America, these changes translate into fewer and shorter droughts under the SSP3-7.0-lowNTCF scenario compared to SSP3-7.0. By contrast, arid and semi-arid regions such as the Sahara and West Asia exhibit a worsening of drought conditions—drought events become more frequent, severe, and prolonged. These outcomes indicate that aerosol-related cooling and its impact on atmospheric circulation may, in some regions, help maintain or strengthen rainfall, so that reducing aerosols can inadvertently diminish that effect and exacerbate water deficits. Indeed, our multi-model ensemble suggests heightened water stress in the Sahara and West Asia under the SSP3-7.0-lowNTCF scenario, underscoring how local feedbacks and large-scale circulation patterns can alter the hydrological response to emission mitigation.

Overall, our findings highlight the non-linear and regionally dependent effects of NTCF mitigation on drought risk. In many regions, curtailing aerosol and ozone-precursor emissions offers co-benefits for air quality and climate adaptation by decreasing drought likelihood; however, arid and semi-arid areas may face more severe drought outcomes.