Abstract
Freshwater shortage already affects large parts of the world, and is expected to increase rapidly over the coming decades as a result of increased water demands and the impacts of climate change. Global-scale water risk or stress maps are available online, but these lack quantitative information on local freshwater availability, rendering them unsuitable for water risk assessment from an operational perspective, i.e. when comparing water availability to a specific quantified water demand (in m3s−1 rather than generic risk indicators). Therefore, our main goal was to develop a rapid screening method to estimate current and future operational freshwater availability using global-scale models. Operational Freshwater Availability (OFWA) was computed using the PCR-GLOBWB global hydrology and water resources model, coupled to a global MODFLOW groundwater model. PCR-GLOBWB was forced with rainfall and temperature fields from the IPSL-CM5A-LR climate model under the RCP6.0 climate scenario, with water demands based on the SSP2 socio-economic scenario. Unique to our study are the downscaling of the coupled PCR-GLOBWB-MODFLOW model to 90 m resolution and the provision of quantitative estimates on long term trends in operational freshwater availability. Our results showed a high, i.e. operationally relevant, accuracy for operational surface water availability, while the uncertainty about operational groundwater availability remained high due to limited availability of subsurface data. With this method, we developed a modelling capacity for rapidly generating scenario-based water availability projections with operational relevance in a rigorous, systematic way, such that it enables like-for-like comparisons. Further refinement is required for accurate estimates of operational groundwater availability.
Highlights
Climate and socioeconomic change affect the amount of water available for irrigation, industry and households, leading to high freshwater stress in large parts of the globe (Haddeland et al 2014; Vörösmarty et al 2000)
The urgency of water stress has been underpinned by a large number of global studies on historic and future water stress based on global hydrological models (Cai and Rosegrant 2002; Döll et al 2003; Falloon and Betts 2010; Gain and Wada 2014; Hanasaki et al 2008; Van Beek et al 2011; Wada et al 2011)
For PCR-GLOBWB, the validation procedure resulted in a rainfall correction factor on the mean river runoff that ranged from 0.77 for the Rhine River to 0.97 for the West Fork of the San Jacinto River for the ERA-Interim_GPCP forcing (Table 1)
Summary
Climate and socioeconomic change affect the amount of water available for irrigation, industry and households, leading to high freshwater stress in large parts of the globe (Haddeland et al 2014; Vörösmarty et al 2000). For example, groundwater stress (Gleeson et al 2012), drought severity (Sheffield and Wood 2007), and upstream storage (Lehner 2011) While these maps provide useful information on water stress at river basin scale, they do not fulfill the need for quantitative data on freshwater availability for local water users, including industrial and civil utilities being more interested in a volumetric metric (m3s−1) rather than a dimensionless risk indicator. Inter-comparison of water availabilities on a like-for-like basis becomes difficult if not impossible within the context of long-term water demand and supply scenarios
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