Spatiotemporal variability of alpine precipitable water over arid northwestern China

For a better understanding of the precipitable water in the arid northwestern China (NWC), we surveyed the water vapour variability on both sides of the alpine range crests based on the Tropical Rainfall Measuring Mission monthly precipitation data (TRMM 3B43). There were 12 target zones and 23 subzones in six mountain systems representatively selected according to alpine hydrogeomorphology. They were used for comparative analyses in time and space. Comparisons between the two sides of the range crests revealed that there is more precipitable water on the south slopes of the Qilian, Altun, Kunlun, and Altai Mountains, on the north slope of the Tian Mountains, and on the east slope of Helan Mountains. High correlations were detected between precipitable water for both sides of the range crests in target zones, while low correlations were found among precipitable water separately averaged in the Kunlun, Tian, and Qilian Mountains including both sides of the range crests. The proportion of precipitable water during the rainy season gradually increased from west to east along the mountains. Temporally, precipitation presented synchronous increases or decreases on the two sides of the range crests in most of the target zones during the time period from 1998 to 2016, and an overall increase in alpine annual precipitable water was found in the area, except for the decrease in the Altun and western Tian Mountains. The summer decay dominated the decrease in these two target zones, while strengthened conveyance was observed in other seasons, especially in spring and autumn, which compensated for, and led to, total increases in precipitable water in most of the target zones. All of the above findings were indicative of differences in vapour transport from outside areas into diverse alpine systems in the arid NWC, which could be schematically evidenced by the spatial patterns of monthly and annual water vapour conveyance retrieved from the TRMM precipitation data.