Effects of small reservoirs on large scale water availability.

Small reservoirs impact on large scale water availability both by supplying water in a distributed sense, and by subtracting water from large reservoirs with large scale water supply functions. Water availability from small and large reservoirs is subject to climate change, which has the potential to alter the relation between small and large reservoirs. For a case study area in semi-arid Brazil, water supply from small reservoirs is found to be more sensitive to climate change than water supply from large reservoirs. Changes in evapotranspiration are more consistent amongst models and its’ effects may dominate effects by more uncertain changes in precipitation. The reduction in water availability from large reservoirs by upstream abstractions by small reservoirs is found to be significant and may increase with unfavourable climate changes, even in an absolute sense.