Recent Trends of Annual Aridity Indices and Classification of Arid Regions with Satellite-Based Aridity Indices

Abstract

Arid (or dryland) regions occupy 41% of Earth’s total land area and are home to more than a third of the world’s population. Most inhabitants of arid regions live in developing countries. In addition, arid regions are highly vulnerable to climate change and human activity. Global warming has the potential to increase arid land area. In most arid regions, desertification, land degradation, and drought are common. An early warning and monitoring system is urgently needed to safeguard human well-being in those regions. This study examined changes of the global distribution of the aridity index (AI) calculated on the basis of meteorological reanalysis and precipitation datasets from 2001 to 2013. Climatically wet regions in arid regions are becoming more arid. Classification of aridity with a satellite-based aridity index (SbAI) characterized present conditions better than classification with the AI. These results suggest that land aridification or wetting can be detected by comparing the SbAI (= actual conditions) with the AI (= climatic conditions).