Climate Change Water Resources Planning Impacts Incorporating Reservoir Surface Net Evaporation Fluxes: A Case Study

The majority of published studies on the impacts of climate change on reservoired water resources systems have concentrated on the influence of the climate- change-modified inflow series. However, for reservoirs the direct net evaporation (i.e. evaporation less rainfall) fluxes on the reservoir surface are also affected by climate change and, depending on the magnitude of the change, could have significant effects on the assessed impacts. In this study, we have performed reservoir storage-yield-reliability planning analyses on two multiple reservoir systems, one in England and the other in Iran, to investigate the possible effects of reservoir surface net evaporation flux for both baseline and climate-change conditions. The results showed that, under baseline conditions, consideration of net evaporation will require lower storages for the English systems and higher storages for the Iranian systems. The practical significance of this is that English systems analysed without consideration of surface fluxes represent an over-design which can provide a buffer against future shortages, whereas the under-design caused by ignoring surface fluxes in the Iranian systems will exacerbate the problem of such shortages. Perturbing the baseline inflow and climatological time-series data using a number of recently published climate-change scenarios produced different impacts at high and low yields for both systems. Possible explanations are offered for these impacts and suggestions are made for further studies.