## 5 Discussion  
There are many contradictory results in various areas of the highlands regarding the increase in temperature in the regions dependent on the elevation. In some mountainous terrain, warming increases with altitude [64; 65]. On the contrary, some studies have revealed that the rate of temperature increase in high mountain areas is lower than in low mountain areas [66; 67]. In our study, the seasonal air temperature analysis revealed an increasing trend in all three stations at different altitudes for most months during the 1960-2018 and 1991-2018 periods. However, for the months of January, February, and December, a decreasing trend was observed in the Anzob climate station, located in the upstream regions of the VRB. This finding is consistent with the results reported in the literature [66; 67]. The mean annual temperature showed a significant increasing trend during all periods in the upstream, midstream, and downstream regions, which is in a line with the findings of the previous studies [64; 65]. For the precipitation trend investigation, in the historical time from 1960 to 2018, a significant upward trend was indicated in January and February in the Anzob station. Similarly to this, [PERSON] et al. [11] and [PERSON] et al. [68] discovered a significant increasing trend in the winter precipitation for the Central Asia region, where they identified an increasing  
Figure 10: The Y axis represents the months of the year and the X axis represents the years. The colors in the heatmap indicate the amount of snow cover, ranging from low (dark colors) to high (light colors), with a range of 0–2000 km\({}^{2}\). trend throughout the 1930-2009, 1960-1991, and 1960-2013 time periods. According to the assessment by [PERSON] et al. (2009), the global winter precipitation increased during the second half of the 20 th century, which can be attributed to the role of increasing moisture counteracted by weakening circulation. Our results showed a decreasing trend in precipitation in April in the upstream, midstream, and downstream regions during the periods 1960-1990 and 1991-2018 in the VRB. The current result is in line with the results of the [PERSON] et al., wherein a significant downward trend was found in October and May during the period 1970-2009 ([PERSON] et al., 2010). The annual precipitation presented a significant decreasing trend during two periods (1991-2018 and 1960-2018) in the upstream region of VRB, while a non-significant positive trend was indicated during the period 1960-1990. Almost all stations during all periods exhibited a downward trend in annual precipitation in the VRB, which corresponds to the results of [PERSON] et al. in the Yellow River Basin in China (2018) and the same statistical trend revealed by [PERSON] et al. (2018) over Central Asia. According to [PERSON] et al. (2018), the MMK trend test revealed a significant upward trend in annual precipitation along the Yangtze River in the Qinghai-Tibet Plateau from 1961 to 2015. These discrepancies in our findings may be attributable to the rising concentration of anthropogenic absorbing aerosols and the prevailing westerlies (west winds in the middle latitudes 30-60\({}^{\circ}\)), including the Asian region ([PERSON] et al., 2010; [PERSON] et al., 2018). We can better understand how climate change and other factors that impact snow energy balance, such as light-absorbing particle deposition, affect snow cover in Central Tajikistan by examining snow cover duration trends. Although patterns differ on a sub-basin scale across the Syr Darya River and the Amu Darya River, changes in precipitation and temperature usually result in less snow accumulation along with earlier snow melt, which combine to result in shorter annual snow cover duration ([PERSON] et al., 2010). Our outcomes of the monthly trend analysis of snow cover indicated an increasing trend in April and July and a stable trend pattern in March, May, August, and October in the Varzob River Basin in Tajikistan, which is in line with the results of [PERSON] et al.