Investigating the global and regional response of drought to idealized deforestation using multiple global climate models

Abstract. Land use change, particularly deforestation, significantly influences the global climate system. While various studies have explored how deforestation affects temperature and precipitation, its impact on drought remains less explored. Understanding these effects across different climate zones and timescales is crucial for crafting effective land use policies aimed at mitigating climate change. This study investigates how changes in forest cover affect drought across different timescales and climate zones using simulated deforestation scenarios, where forests are converted to grasslands. The study utilizes data from nine global climate models, including BCC-CSM2-MR, CMCC-ESM2, CNRM-ESM2-1, CanESM5, EC-Earth3-Veg, GISS-E2-1-G, IPSL-CM6A-LR, MIROC-ES2L, and UKESM1-0-LL, which contribute to the Land Use Model Intercomparison Project (LUMIP). Drought effects are assessed by examining the Standardized Precipitation Evapotranspiration Index (SPEI) in the idealized global deforestation experiment (deforest-global) using the pre-industrial control simulation (piControl) as the reference. At the 3-month scale (SPEI03), global SPEI responses to deforestation are negative overall, indicating increased dryness conditions, particularly in tropical regions, while causing wetter conditions in dry regions. The multi-model ensemble mean (MME) of SPEI03 is -0.19±0.05 (mean ± standard deviation) in tropical regions and 0.07±0.05 in dry regions. The impact on drought conditions becomes more significant over longer timescales. In tropical regions, the MME of SPEI at the 24-month scale is -0.39±0.07, while it is 0.19±0.08 in dry regions, highlighting the lasting effects of deforestation on drought conditions. Seasonal responses of SPEI03 to deforestation are more pronounced during autumn and winter, with especially significant effects observed in tropical and northern polar regions. For the MME of SPEI03, the values in tropical regions are -0.24±0.08 and -0.18±0.07, while, in northern polar regions, they are -0.16±0.07 and -0.20±0.08, respectively. Continental zones experience significant seasonal changes, becoming drier in winter and wetter in summer due to global deforestation, while the Northern Hemisphere's dry regions see increased wetter conditions, particularly in autumn. Deforestation alters surface albedo by changing surface land cover structure, which affects the surface energy and water balance by modifying net solar radiation, evapotranspiration, and precipitation patterns. These changes affect water deficits, leading to varying drought responses to deforestation. The findings deepen our understanding of the relationship between vegetation change and climate change, offering valuable insights for better resource management and mitigation strategies against future climate change impacts.