Elevation Dependency of Climatic Variables Trends in the Last Decades in the Snow-Fed and Glacier-Fed Vakhsh River Basin, Central Asia

Given the various altitudes of the Vakhsh River Basin (VRB) in Central Asia, global warming has significant implications for water resources and environmental changes as most snow surfaces and glaciers are situated above 3000 m above sea level in the catchment. The aim of this study is to use observational climate data to evaluate the response of low- and high-altitude areas in the VRB to climate warming through assessment of annual mean air temperature and annual mean precipitation trends and magnitudinal variability. The long-term hydro-climatic variables are evaluated employing the original Mann-Kendall test, modified Mann-Kendall (MMK) test, and Sen’s slope estimator. The general pattern of the annual mean air temperature reveals continuous warming in the catchment over the 1934–1995 and 1960–2015 time periods. The MMK test result shows a statistically significant increase in the annual mean air temperature trend in the low elevation stations during the 1960 to 2015 time period. Similarly, at the alpine N.P. Gorbunov (Fedchenko Glacier) climate station at 4162 m, the annul mean temperature exhibits a statistically significant increasing trend during the 1934–1995 time period with a Kendall statistic ( Z ) of 7.266 and a slope value of 0.010. The results of the MMK test reveal a statistically significant decrease in the annual mean precipitation trend solely in one station with a Z of –2.385 and a slope value and p- value of –1.273 and 0.017, respectively. However, the results of the MMK test exhibit a statistically significant increasing trend in annual mean precipitation in the high-elevation stations such as Lyakhsh and N.P. Gorbunov with Z values of 6.367 and 6.818, slope values of 1.530 and 8.824, and p- values of 0.000 and 0.000, respectively. These findings show pronounced climatic change in the VRB. The long-term data analysis indicates changes in air temperature and precipitation conditions; thereby, the results provide guidance for planning new national mitigation and adaptation activities.