Abstract:The aridity Index (AI, here defined as the climatic aridity) is an index that describes the dry and wet conditions of a site. Historically, the AI has been often used in long-term studies of geography and ecology. Recently it has became one of the most frequently used climatic factors in studies of global change, especially in studies of climate change, ariditification and desertification. A total of 22 AIs used worldwide were briefly introduced in this paper, and of these eight of the more commonly used AIs were evaluated. We discussed their principles, calculation methods, their applications in ecological and geographical studies, and the advantages and shortcomings of each indice were analyzed based on their applications and practice in China. Our analyses indicated that three AIs, the modified Selianinov AI, the de Martonne AI and the Holdridge potential evapotranspiration ratio (another AI to some extent) have clear applicability and significance for physics and ecology. These AIs are suitable for characterizing the physical environment of China and can be used in future studies of climate change, aridification and desertification in China.