Global changes in potential evapotranspiration (1992–2020) and associated drivers: Shuttleworth-Wallace model-based analysis

Abstract

Based on the Shuttleworth–Wallace model, which has considerations of sophisticated physical processes and involves impacts of vegetation dynamics, changes in land use/cover (LUCC) and CO₂ physiological effects, here we investigated the spatial–temporal characteristics of annual potential evapotranspiration (PET) and its two components (potential transpiration (PT) and soil evaporation (PE)) during 1992–2020 and identified their underlying drivers. Globally, the annual PET was 1276.91 mm, with the annual ratios of PT and PE to PET of 44 % and 56 %, respectively. The global mean annual PET, PT, and PE significantly increased by 1.12 mm/yr, 0.44 mm/yr, and 0.67 mm/yr, respectively. Over 48 % of global land, the annual PET changes were controlled by PT, but the rest by PE. Attribution analyses indicated that air temperature was the major contributor of the global mean annual PET, PT, and PE increases, but the determinant factors differed spatially. Although the climate factors as the main contributors of the changes in the three variables had the largest area percentage, more than 16 % of global land showed the dominant factors of Leaf Area Index, CO₂, and LUCC, especially for annual PT and PE changes with an area percentage exceeding 30 %. This study underlines the necessity of separating PET into PT and PE components and examining them individually to better understand PET changes. Also, it provides new and significant insights for an in-depth understanding of PET’s changes from perspectives of changes in climate and vegetation (e.g., vegetation greening and CO₂ physiological effects), as well as LUCC.