An integrated model for the assessment of global water resources Part 1: Model description and input meteorological forcing

Abstract

To assess global water availability and use at a subannual timescale,an integrated global water resources model was developed consistingof six modules: land surface hydrology, river routing, crop growth,reservoir operation, environmental flow requirement estimation, andanthropogenic water withdrawal. The model simulates both naturaland anthropogenic water flow globally (excluding Antarctica) on adaily basis at a spatial resolution of 1 degrees x 1 degrees (longitudeand latitude). This first part of the two-feature report describesthe six modules and the input meteorological forcing. The input meteorologicalforcing was provided by the second Global Soil Wetness Project (GSWP2),an international land surface modeling project. Several reportedshortcomings of the forcing component were improved. The land surfacehydrology module was developed based on a bucket type model thatsimulates energy and water balance on land surfaces. The crop growthmodule is a relatively simple model based on concepts of heat unittheory, potential biomass, and a harvest index. In the reservoiroperation module, 452 major reservoirs with >1 km(3) each of storagecapacity store and release water according to their own rules ofoperation. Operating rules were determined for each reservoir byan algorithm that used currently available global data such as reservoirstorage capacity, intended purposes, simulated inflow, and waterdemand in the lower reaches. The environmental flow requirement modulewas newly developed based on case studies from around the world.Simulated runoff was compared and validated with observation-basedglobal runoff data sets and observed streamflow records at 32 majorriver gauging stations around the world. Mean annual runoff agreedwell with earlier studies at global and continental scales, and inindividual basins, the mean bias was less than +/- 20% in 14 ofthe 32 river basins and less than +/- 50% in 24 basins. The errorin the peak was less than +/- 1 mo in 19 of the 27 basins and lessthan +/- 2 mo in 25 basins. The performance was similar to the bestavailable precedent studies with closure of energy and water. Theinput meteorological forcing component and the integrated model providea framework with which to assess global water resources, with thepotential application to investigate the subannual variability inwater resources.