Abstract: The parameters in the temperature-based Hargreaves method for the estimation of potential evapotranspiration(ET_P)are calibrated by the FAO Penma-Monteith method and daily data during the period 1959-2008 at 20 meteorological stations in the Weihe River basin.To study the impact of(limate(hangs on potential evapotranspiration, the projected daily maximum and minimum air temperature(T_max/T_min)of HadCM3 CCM under A2 and B2 scenarios are first downscaled onto local meteorological stations using the statistical downscaling model(SDSM).Using the calibrated Hargreaves method,the future ET_P,T_max and T_min time series under A2 and B2 scenarios can then be calculated.The spatiotemporal characteristics of these series are analyzed.Results show that the calibrated Hargreaves method reproduces well the observed potential evapotranspiration at each of the 20 meteorological stations;upward trends in daily T_max and T_min and annual ET_P could be significant compared to that of the baseline period 1961-1990 under both scenarios;the increase in meteorological variables would be greater under A2 than B2;over different regions of the Wei River basin,the annual ET_P could be gradually increasing for the three future periods,the 2010-2039,the 2040-2069 and the 2070-2099;and the greatest increase of ET_P could be expected in the south bank of the basin, while the lowest increase might be found in the north bank.