Assessing runoff in future climate conditions in Messara valley in Crete with a rainfall-runoff model.

The aim of this study is to develop a relationship between rainfall and surface water (runoff) in South Crete, Greece. This application was carried out on five sub-basins in the Messara valley, with a total surface of 1125 km². Three factors were taken into account: the climate regime including precipitation and air temperature, the geological nature of the ground and the surface area of the basin. The development of the rainfall-discharge model consisted of three steps. Firstly, the actual evapotranspiration ( E_r) was computed. Secondly, the storage capacity of each hydrogeological unit in every catchment area was geologically estimated and, lastly, the rainfall-runoff model was developed using the water balance equation and the above mentioned relationship of E_r. The amount of variance in runoff between the sub-basins explained by those three factors was 92%. Decreases in mean annual precipitation by 17 and 15% for east and west Messara, respectively, predicted by the regional climate model REMO resulted in even more drastic mean runoff reductions by 29 and 32% at the respective sides of the valley. Furthermore, the coefficient of variation of runoff increased by more than 15% in the east side of the valley but dropped by only 1.5% in the west. The proposed rainfall-discharge relationship is a useful tool for hydrological management and evaluation of water resources under the present-day and future climate conditions in Messara valley in Crete. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]