Spatiotemporal changes in global aridity in terms of multiple aridity indices: An assessment based on the CRU data

Aridity is a complex environmental hazard, posing potential risks to more than 38% of the world's population in terms of poverty, reduction in crop and livestock production, water scarcity, and loss of biodiversity. Despite its complex nature and the subsequent adverse impacts, limited attention has been given to studying the aridity phenomenon, in terms of multiple aridity indices. The present study assessed spatiotemporal changes in global aridity over the period 1901–2019, using five aridity indices, i.e., De Martonne aridity index (AIDM), Emberger aridity index (AIE), Erinç aridity index (AIM), the Pinna combinative aridity index (AIP), and United Nations Environment Programme (UNEP) aridity index (AIUNEP). The study's findings revealed that the maximum intensity and expansion of global aridity have been observed in the recent decades (1991–2019), with major hotspots of aridity located in the equator and subtropical zones of the world. Except for the AIUNEP index, the rest of the indices displayed an obvious and consistent increase in aridity over Northern Hemisphere. The increase (decrease) in temperature (soil moisture) has intensified the process of potential evapotranspiration (PET) and aridity across the globe. Though the selected indices characterize the aridity patterns and their intensities with high spatial variability; therefore, these indices need to be applied at regional and local scales for more robust results, and better planning, adaptation, and mitigation measures to ensure sustainability in agriculture and water resources. A detailed assessment along with a numerical model experiment is also required for a conclusive quantification of the relative influence of the associated variables in the variability of aridity over different regions of the world.