Water shortages worsened by reservoir effects

The expansion of reservoirs to cope with droughts and water shortages is hotly debated in many places around the world. We argue that there are two counterintuitive dynamics that should be considered in this debate: supply–demand cycles and reservoir effects. Supply–demand cycles describe instances where increasing water supply enables higher water demand, which can quickly offset the initial benefits of reservoirs. Reservoir effects refer to cases where over-reliance on reservoirs increases vulnerability, and therefore increases the potential damage caused by droughts. Here we illustrate these counterintuitive dynamics with global and local examples, and discuss policy and research implications. Reservoirs are frequently posited as a method of increasing water supplies, especially in arid areas. However, they may be inducing and enabling demands for water through increased population and economic activity, and these demands can surpass even the supply that the reservoir can provide and counterintuitively make the areas more vulnerable to drought conditions.