Abstract: The Weihe River Basin, with an obvious horizontal and vertical zonality of climate, is distributed in three climatic zones including the temperate, warmtemperate semiarid and warmtemperate semihumid zones in the Guanzhong region. Annual temperature decreases gradually from the south to the north and from the lowland to the highland, and its average was in a range of 7.8-13.5 ℃. Affected by topography, precipitation in the drainage basin is limited and distributed unevenly with obvious seasonal and annual changes, and the annual precipitation is in a range of 450-700 mm. Annual potential evaporation is 700-1 200 mm, and the frostfree season is for 120-220 days. Surface runoff in the Weihe River Basin comes mainly from precipitation, and its distribution is consistent with precipitation. The average annual runoff volume is 62.2×108 m3, and more than 55% of which is from Qinling Mountains. Surface water resources is poor at the Weihe River plain and the north Shaanxi Loess Plateau, and the annual runoff depth is only 10 to 25 mm. In this paper, the crop water stress index (CSWI) method was used to monitor drought in the Weihe River Basin, and the derived involving potential evapotranspiration (ETp) and actual evapotranspiration (ETa) parameters were introduced. Based on the results, the drought conditions in the Weihe River Basin were studied, and the results were validated with the observed data. The monitoring results are follows: ① The model was validated by comparing the simulated data with the observed data, and the correlation coefficient was 0.80. These results reflect the effectiveness of the model; ② Drought in the Weihe River was slight in 2006, 2007 and 2009 and moderate in 2008; the CSWI was decreased from March to July, and increased gradually from August to December; ③ For the different vegetation types, the CSWI of woodland was the highest, that of grassland and farmland was similar, and drought was slight.  

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