An integrated model for the assessment of global water resources – Part 2: Applications and assessments

摘要

To assess global water resources from the perspective of subannual variationin water availability and water use, an integrated water resources model wasdeveloped. In a companion report, we presented the global meteorologicalforcing input used to drive the model and six modules, namely, the landsurface hydrology module, the river routing module, the crop growth module,the reservoir operation module, the environmental flow requirement module,and the anthropogenic withdrawal module. Here, we present the results of themodel application and global water resources assessments. First, the timingand volume of simulated agriculture water use were examined becauseagricultural use composes approximately 85% of total consumptive waterwithdrawal in the world. The estimated crop calendar showed good agreementwith earlier reports for wheat, maize, and rice in major countries ofproduction. In major countries, the error in the planting date was ±1mo, but there were some exceptional cases. The estimated irrigation waterwithdrawal also showed fair agreement with country statistics, but tended tobe underestimated in countries in the Asian monsoon region. The resultsindicate the validity of the model and the input meteorological forcingbecause site-specific parameter tuning was not used in the series ofsimulations. Finally, global water resources were assessed on a subannualbasis using a newly devised index. This index located water-stressed regionsthat were undetected in earlier studies. These regions, which are indicatedby a gap in the subannual distribution of water availability and water use,include the Sahel, the Asian monsoon region, and southern Africa. Thesimulation results show that the reservoir operations of major reservoirs(>1 km3) and the allocation of environmental flow requirements canalter the population under high water stress by approximately −11% to+5% globally. The integrated model is applicable to assessments ofvarious global environmental projections such as climate change.