Regional characteristics of compound hot and dry event: its present and future

Abstract

Compound hot and dry (CHD) events have various impact on society and ecosystems in various ways, such as wildfires, agricultural losses, water scarcity, and increased mortality. Likelihood of these CHD events is projected to increase more frequently in more extensive regions in the future. Previously, projection of the likelihood and understanding of characteristics such as severity and duration of these events were investigated. However, it is unclear which climate driver more contributes to the increasing trend of the CHD events. In other words, one can ask if dry trend during warm season is possibly caused by precipitation deficit or excess evapotranspiration, or both. Therefore, regions which become significantly drier during the warm season based on historical observation were identified first, and their future at the end of the 21st century are projected. The Standardized Precipitation Evapotranspiration Index (SPEI) is used here, because it is calculated based on atmospheric water deficit, i.e., Precipitation – Evapotranspiration. Further, separation of P and E from SPEI can shed light on the role played by each variable in the CHD events. The identified regions were classified into three types based on future behavior patterns of precipitation and evapotranspiration. Type I for precipitation-driven; Type II for evapotranspiration-driven; Type III for precipitation and evapotranspiration-driven. Each type of region experiences different potential risk. TYPE I are P-driven regions, and the regions could be vulnerable to meteorological drought that influenced by the deficiencies of precipitation during warm season. While TYPE II are E-driven, so these regions could experience CHD events more frequently in the future possibly due to excess evapotranspiration. According to the seasonal stripes of TYPE II, the compensation precipitation during non-dry season was critical in evolving drought condition in some regions of TYPE II. And the others of TYPE II were projected that the rate of drying due to evapotranspiration would outpace the rate of increase in precipitation. Meanwhile, TYPE III are P&E-driven, so precipitation will decrease and evapotranspiration will be active, which creating conditions that are bound to be drier in warm season. Since the projection of P and E of TYPE III is the worst scenario, the region could be chronically suffered from drought at the end of the 21st century. The result of this study generally confirms findings in the Intergovernmental Panel on Climate Change (IPCC)’s 6th Assessment Report. Identifying contributing climatic driver at a specific region is critical in projection of correspondent potential future risk and eventually applying proper measure regionally. However, certain limitations also exist. For example, projected climate by coupled climate models have uncertainty and bias. Also, disagreement exists between reanalysis data and historical simulation of model data.