Abstract
Atmospheric precipitation is an important part of the water circle in an inland basin. Based on the analytical results of 149 precipitation samples and corresponding surface meteorological data collected at four sampling sites (Lenglong, Ningchang, Huajian and Xiying) at different elevations in the Xiying river basin on the north slope of Qilian Mountains from May to September 2017, the sub-cloud evaporation in precipitation and its controlling factors are analyzed by the Stewart model. The results show that sub-cloud evaporation led to d-excess value in precipitation decrease and d-excess variation from cloud-base to near surface (Δd) increase with decreasing altitude. The remaining evaporation fraction of raindrop (f) decreases with decreasing altitude. The difference of underlying surface led to a difference change of f and Δd in the Xiying sampling site. For every 1% increase in raindrop evaporation, d-excess value in precipitation decreased by about 0.99‰. In an environment of high relative humidity and low temperature, the slope of the linear relationship between f and Δd is less than 0.99. In contrast, in the environment of low relative humidity and high temperature, the slope is higher than 0.99. In this study, set constant raindrop diameter may affect the calculation accuracy. The Stewart model could have different parameter requirements in different study areas. This research is helpful to understand water cycle and land–atmosphere interactions in Qilian Mountains.
Highlights
In a cold-alpine region, runoff is mainly fed by Cryosphere meltwater and precipitation [1]
Placing a table reaches of Xiying river basin (Lenglong, Ningchang and Huajian), d-excess values at near surface decreased with decreasing altitude, and Δd increased with decreasing altitude
The change of d-excess at near surface and Δd show opposite trends compared with those of middle and upper reaches, which may be caused by different underlying surfaces. d-excess values at near surface were much lower than that in the cloud-base, indicating that sub-cloud evaporation plays a tennis ball in the collection funnel sealed the collector bottle against evaporation and debris
Summary
In a cold-alpine region, runoff is mainly fed by Cryosphere meltwater (glaciers, snow, permafrost) and precipitation [1]. Almost all glaciers in the world are shrinking, the thicknesses of permafrost active layers are increasing, and snow cover extent and duration are decreasing [2]. In the alpine region of northwest China, which is the main distribution area of Cryosphere (including glacier, permafrost and snow cover), the annual mean surface temperature has risen by 1.8 ◦ C from 1960 to 2007 [3]. The area of glaciers, permafrost and snow cover in Qilian Mountains has decreased significantly [4,5,6]; on the contrary, precipitation is increasing.
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