GlobWat – a global water balance model to assess water use in irrigated agriculture

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.

Recent changes in terrestrial water storage in the Upper Nile Basin: an evaluation of commonly used gridded GRACE products

“…Estimates of mean annual evaporation from the surface of Lake Victoria vary from 1260 mm (UNEP, 2013) to 1566 mm (Hoogeveen et al, 2015), whereas mean annual evaporation from the surface of Lake Kyoga is estimated to vary from 1205 mm (Brown and Sutcliffe, 2013) to 1660 mm (Hoogeveen et al, 2015). Evapotranspirative fluxes from the surrounding swamps in Lake Kyoga are estimated to be much higher and approximately 2230 mm yr −1 (Brown and Sutcliffe, 2013).…”

Hydrological consequences of natural rubber plantations in Southeast Asia

“…Rubber's crop parameters, values of kc , and crop calendar were taken from Chapagain and Hoekstra (), while rooting depth and depletion factor were taken from Allen et al (). Parameters for land use other than crop type (i.e., forests and tree cover, herbaceous areas and shrubs, water, and artificial areas) were taken and adjusted from Hoogeveen et al (). Please, see Table S3.…”

Response to Anonymous Referee 1 (AR1)

“…Estimates of mean annual evaporation from the surface of Lake Victoria vary from 1260 mm (UNEP, 2013) to 1566 mm (Hoogeveen et al, 2015), whereas mean annual evaporation from the surface of Lake Kyoga is estimated to vary from 1205 mm (Brown and Sutcliffe, 2013) to 1660 mm (Hoogeveen et al, 2015). Evapotranspirative fluxes from the surrounding swamps in Lake Kyoga are estimated to be much higher and approximately 2230 mm yr −1 (Brown and Sutcliffe, 2013).…”

“…1) surface water storage in rivers, lakes, and wetlands ( SWS), soil moisture storage ( SMS), ice and snow water storage ( ISS), and groundwater storage ( GWS). Over the last decade, GRACE measurements have become an important hydrological tool for quantifying basin-scale TWS (Güntner, 2008;Xie et al, 2012;Hu and Jiao, 2015) and are increasingly being used to assess spatio-temporal changes in specific water stores Shamsudduha et al, 2012;Jiang et al, 2014;Castellazzi et al, 2016;Long et al, 2016;Nanteza et al, 2016) where timeseries records of other individual freshwater stores are available (Eq. 1).…”