The key drivers for the changes in global water scarcity: Water withdrawal versus water availability

Water scarcity has become a major issue to sustainable development. It can be estimated by available fresh water resources and human water withdrawal, which are affected by both climate change and human activities. However, the key drivers for the changes in water scarcity at global scale remain unclear due to large uncertainties in the estimations of the contributions from changes in water withdrawal and water availability. By using a newly reconstructed water withdrawal dataset and multi-model simulations of water availability, this study assessed global water scarcity evolution during 1971-2010 at half degree resolution and monthly time scale by applying the water stress index (WSI). Results showed that WSI increased in areas with 61.1% of global population during 1971-2010, and the increase in water withdrawal (especially agricultural sector) was the key driving factor for areas with 57.5% of global population. Specifically, growing water withdrawal led to increased water scarcity for areas with 21% of global population in spite of rising water availability resulted from climate change, such as in southeastern China, Southeast Asia, southern India, and Central Africa. In contrast, water scarcity mitigated over some developed areas including parts of USA, Europe and Japan with 8.8% of global population, which resulted from decreased human water withdrawal (especially industrial sector) and increased water availability. This study reveals the synergistic or contrary effects of changes in water withdrawal and water availability on the changes in water scarcity over the globe, and provides useful information for regional water planning and management.