44. Hydrological Impacts of Changes in Evapotranspiration and Precipitation: Two Case Studies in Semi-arid and Humid Climates

A simple water balance model was used to examine the impact of changes in regional evapotranspiration E, and precipitation P, on water yield (i.e. surface runoff and groundwater recharge) Y, and irrigation water requirements I, in a humid clmate at Valentia, Ireland, and in a semi-arid climate at Bet Dagan, Israel, using more than 40 years of monthly precipitation and Class A pan evaporation data. Statistically significant time trends existed for precipitation at Valentia and for pan evaporation at Bet Dagan. A negative correlation between P and E existed at both sites and had a considerable effect on computed water yield in the humid climate and on irrigation water amounts in the semi-arid climate. Periods of water stress reduced the negative correlations between P and E, even leading to positive correlations on occasions. Statistical distribution functions were used to determine water yield and irrigation water requirements for return periods of 5, 10 and 50 years, allowing more precise planning of water infrastructures.