Relationship of Drought and Engineered Water Supply: Multivariate Index for Quantifying Sustained Water Stress in Anthropogenically Affected Subbasins

AbstractDrought occurs across all climates worldwide, but has different impacts from one region to another. Because water is the most basic of human needs, drought and water shortage can result in severe socioeconomic difficulties that take years to overcome. While drought has traditionally been classified on the basis of deficiencies in precipitation, with the advent of climate change and the increase in evapotranspiration that is occurring, efforts have been made to focus instead on derived soil moisture anomalies. A less recognized factor modulating soil moisture anomalies is the use of engineered water supply, through canals or river diversions, and also through groundwater pumping. This paper attempts to formulate a multivariate metric of sustained water stress severity that attempts to incorporate these additional sources of water supply in engineered subbasins. The proposed index uses entropy theory as the basis of its formulation, and was compared against traditional indexes, and the differences were noted. Remotely sensed vegetation products were used as an independent means of assessing the validity of the proposed index. It was found that the proposed index collapses to the more traditional drought indexes in subbasins without significant unnatural water supply, while presenting a more accurate picture of water stress in subbasins where engineered water supply is present, as interpreted by the vegetation (or its lack thereof) the water supply is able to sustain.