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This paper quantifies the contribution of climatic factors to potential evapotranspiration (ET0) under different drought periods by making use of the FAO Penman-Monteith method, linear regression analysis, Mann-Kendall test, and the drought classification derived from the Standardized Precipitation Index (SPI). ET0 and meteorological data from 93 North China weather stations from 1961 to 2010 located in a semi-arid climate zone were analyzed. The annual ET0 values showed a significantly increasing trend with the aggravation of drought. Results indicated that in drought periods, temperature and sunshine hours had positive effects on the variation of ET0, while other key climatic factors (i.e. effective precipitation, vapor pressure, wind speed, relative humidity) had negative effects on ET0. ET0 was most sensitive to effective precipitation and mean daily temperature, with sensitivity rates of -4.163 and 1.368 respectively. The sensitivities of ET0 decreased over time in the drought period, which was caused by the joint effects of the climatic factors. The decreasing sensitivity of wind speed and relative humidity increased the ET0, and the increase of daily temperature produced the majority of rise in ET0 rates. The decrease of wind speed and relative humidity resulted in positive contributions to ET0. The increase in the sensitivity of precipitation and vapor pressure resulted in strongly decreased ET0, and the decrease of sunshine hours resulted in little change in ET0 rates. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.