Abstract: In the arid area,the sub-cloud secondary evaporation usually occurs to the raindrops. It is important to understand the variation of the stable hydrogen and oxygen isotopes of the raindrops when they travel from cloud-base to the ground in the isotope hydrological studies. Based on the hourly meteorological observations from the meteorological stations in Xinjiang, China, the temporal and spatial characteristics of the sub-cloud evaporation residue ratio(which is the ratio of the residual volume of the raindrops after the evaporation as they travel from cloud-base to the near-surface to the original volume, f),the δD variation(△δD) of the raindrops and the deuterium excess change(△d)were analyzed by using the modified Stewart model. The relationship between △d and meteorological parameters as well as the sensitivity analysis of △d were also analyzed. The results showed as follows:(1)The values of △d and f present spatial dependency in Xinjiang.(2) Under the conditions of low temperature,high relative humidity,high rainfall intensity and large raindrop diameter,f is usually large and △d is close to 0. The linear relationship between f and △d is evidenced and the slope is low. However the regression coefficients are not always stable under different meteorological conditions,thus the inversion computation of the parameter f based on this linear relationship should be treated with caution.(3)The sensitivity analysis indicates that,if the temperature was increased by 2℃,△d was decreased by 0.26‰-3.10‰;If the relative humidity was increased by 5%,△d was increased by 1.23‰-8.34‰;If precipitation intensity was increased by 10%,△d was increased by 0.06‰-0.89‰;If the raindrop diameter was increased by 0.2 mm,△d was increased by 0.98‰-8.16‰. However,if the raindrop diameter was larger than 1.2 mm,△d tended to be stable.

Key words: Xinjiang, precipitation, stable isotope, sub-cloud evaporation, deuterium excess