A network of consultants in hydrology, hydrogeology, water quality and water resources

Effects of different scenarios

Whilst there may be some scope for disagreement as to the causes of climate change, there is now a general consensus among scientists as to the magnitude and nature of these changes. This consensus is so strong that water companies could be accused of neglect of duty were they not to evaluate the effects of these changes on the reliable yield of their resources

In an earlier project Water Resource Associates had calibrated the HYSIM rainfall/runoff model to the rivers forming the main surface water resources of Severn-Trent (the second largest water company in the UK). These flows had been used with the RESSIM model, also developed by WRA, to evaluate the deployable yield of the company's resources. For this project four climate change scenarios (low, medium low, medium high and high) were simulated for two time horizons (2020 and 2050). As the HYSIM model is physically realistic it was able to represent the effects of changes in PET and precipitation.

The rivers upstream of the main control points were simulated as a number of sub-catchments (12 in the case of the Severn and 6 in the case of the Derwent) to preserve hydrological and meteorological heterogeneity. For each of these sub-catchments a daily flow record from 1918 to 1997 was produced. In addition to the basic scenarios the simulations were carried out for both absolute and percentage changes. The model also produced simulated soil and groundwater storage and groundwater recharge for the same period.