Abstract:The Gurbantonggut Desert, China, is an ideal site for study of sublimation from the snowpack because there are sparse vegetation and simple topography, and the wind speed is not large enough to blow snow into the atmosphere from the snowpack. Daily sublimation was measured by manual snow lysimeters at 8:00, and an automatic weather station was deployed at the top of a stout longitudinal dune chain at the southeastern edge of the desert. It is shown that on a daily scale, there was an extremely significant no-intercept linear relationship between the measured sublimation and that calculated by the bulk aerodynamic method, although the former was only 83.8% of the latter. It is also demonstrated that À10 C and 2 m/s were the thresholds where the sublimation varied with the air temperature and the wind speed. When these two thresholds were exceeded, the sublimation accelerated. However, the air temperature and the wind speed at 2 m above the ground averaged À17.2 C and 1.3 m/s, respectively, and the percentages of the time when the air temperature was below À10C and the wind speed was below 2 m/s were 76.9% and 85.1%, respectively. As a result, the rate of sublimation was quite low most of the time, and the thin snowpack remained in a quasi-static state until the melt stage started.

The source region of the Yangtze River (SRYR) on the central Tibetan Plateau has seen one of the most significant increases in temperature in the world. Climate warming has altered the temporal and spatial characteristics of precipitation in the SRYR. In this study, we analyzed the temporal trends and spatial distributions of extreme precipitation in the SRYR during 1960–2016 using 11 extreme precipitation indices (EPIs) derived from daily precipitation data collected at five meteorological stations in the region. The trends in the EPIs were estimated using the linear least squares method, and their statistical significance was assessed using the Mann–Kendall test. The results show the following. Temporally, the majority of SRYR EPIs (including the simple daily intensity index, annual maximum 1-day precipitation (RX1day), annual maximum 5-day precipitation (RX5day), very wet day precipitation, extremely wet day precipitation, number of heavy precipitation days, number of very heavy precipitation days, and number of consecutive wet days) exhibited statistically nonsignificant increasing trends during the study period, while annual total wet-day precipitation (PRCPTOT) and the number of wet days exhibited statistically significant increasing trends. In addition, the number of consecutive dry days (CDD) exhibited a statistically significant decreasing trend. For the seasonal EPIs, the PRCPTOT, RX1day, and RX5day all exhibited nonsignificant increasing trends during the wet season, and significant increasing trends during the dry season. Spatially, changes in the annual and wet season EPIs in the study area both exhibited significant differences in their spatial distribution. By contrast, changes in dry season PRCPTOT, RX1day, and RX5day exhibited notable spatial consistency. These three indices exhibited increasing trends at each station. Moreover, there was a statistically significant positive correlation between the annual PRCPTOT and each of the other EPIs (except CDD). However, the contribution of extreme precipitation to annual PRCPTOT exhibited a nonsignificant decreasing trend.

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