The monthly blue water footprint compared to blue water availability for the world's major river basins
Conventional blue water scarcity indicators suffer from four weaknesses: they measure water withdrawal instead of consumptive water use, they compare water use with actual runoff rather than natural (undepleted) runoff, they ignore environmental flow requirements and they evaluate scarcity on an annual rather than a monthly time scale. In the current study, these shortcomings are solved by defining blue water scarcity as the ratio of blue water footprint to blue water availability – where the latter is taken as natural runoff minus environmental flow requirement – and by estimating all underlying variables on a monthly basis. In this study we make for the first time a global estimate of the blue water footprint of humanity at a high spatial resolution level (a five by five arc minute grid) on a monthly basis. In order to estimate blue water scarcity at river basin level, we aggregated the computed monthly blue water footprints at grid cell level to monthly blue water footprints at river basin level.