Abstract
Abstract. GlobWat is a freely distributed, global soil water balance model that is used by the Food and Agriculture Organization (FAO) to assess water use in irrigated agriculture, the main factor behind scarcity of freshwater in an increasing number of regions. The model is based on spatially distributed high-resolution data sets that are consistent at global level and calibrated against values for internal renewable water resources, as published in AQUASTAT, the FAO's global information system on water and agriculture. Validation of the model is done against mean annual river basin outflows. The water balance is calculated in two steps: first a "vertical" water balance is calculated that includes evaporation from in situ rainfall ("green" water) and incremental evaporation from irrigated crops. In a second stage, a "horizontal" water balance is calculated to determine discharges from river (sub-)basins, taking into account incremental evaporation from irrigation, open water and wetlands ("blue" water). The paper describes the methodology, input and output data, calibration and validation of the model. The model results are finally compared with other global water balance models to assess levels of accuracy and validity.
Highlights
Modelling of the world’s hydrological cycle is important to assess, among others, water resources availability and the sustainability of their use, the impact of climate change, and the influence on global food production (Wood et al, 2011)
Agriculture accounts for about 70 % of the freshwater withdrawals in the world (FAO, 2013), while consumptive use of water in agriculture accounts for about 90 % of all of the water that is evaporated as a result of human intervention
As part of the AQUASTAT programme, Food and Agriculture Organization (FAO) distributes and contributes to the maintenance and development of the Global Map of Irrigation Areas (Siebert et al, 2007, 2010, 2013), which is compatible with AQUASTAT country figures for areas equipped for irrigation
Summary
Modelling of the world’s hydrological cycle is important to assess, among others, water resources availability and the sustainability of their use, the impact of climate change, and the influence on global food production (Wood et al, 2011). Almost all of them are developed at a spatial disaggregation (30 arcmin or coarser) which is not directly comparable with the heterogeneity and spatial variability of irrigation as captured in the FAO’s high-resolution (5 arcmin) Global Map of Irrigation Areas or in other global agriculture land use data such as that available through FAO and IIASA’s Global Agro-Ecological Zones portal (FAO/IIASA, 2012) To overcome this incompatibility between global hydrological models and the Global Map of Irrigation Areas, Siebert and Döll (2008, 2010) developed the Global Crop Water Model (GCWM) to calculate irrigated crop water requirements on a grid resolution of 5 arcmin by using the MIRCA2000 data set (Portmann et al, 2008). The model is designed to complement other FAO data sets and models as used for AQUASTAT (FAO, 2013), Global Agro-Ecological Zones (FAO/IIASA, 2012) and Global Perspective Studies (FAO, 2006, 2011a)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
