Global Hydrological Cycle and World Water Resources

Abstract

Water resources utilize a part of hydrologic cycle on the Earth and the amount of flux (flow) is relevant rather than the stock. Fresh water with required quality is valuable only when available where and when water demand exists since the unit price of water is inexpensive. Virtual water should be considered for world water resources assessment, and some estimates related to Japan are presented. Future balance of the demand and supply of world water resources is also presented using land surface models associated with Total Runoff Integrating Pathways (TRIP) and country-base statistics in 0.5 degree by 0.5 degree longitude/latitude resolution. Purification and desalinization to produce safe fresh water is of course one of promising technology expected in the era of "water crisis." However, the necessary amount of drinking water is limited, and further reduction of the cost to produce municipal water should be required for membrane technology to have its popularity.