Temporal-spatial variability of modern climate in the Altai Mountains during 1970-2015

Association between atmospheric circulations and climate information The temperature trends in the Altai Mountains were similar with that in the Northern Hemi- sphere in recent decades and both experienced a warming climate. The rising rate of tempera- ture was the quickest in spring, which was attributable to the substantially declined snow cover in the past 30 years, especially in early spring through summer interval [52–54]. Fossil fuel and biofuel emissions of black carbon plus organic matter were mainly responsible for spring-time snow cover loss over Eurasia including the Altai Mountains [55]. Although three features of monthly precipitation were existed in the Altai Mountains, MAP was featured by an insignif- icantly increasing trend, which is inconsistent with the wetting Tianshan Mountains [9]. Regional precipitation variability in the Altai Mountains could be closely related with atmo- sphere circulation. Xu et al. [9] calculated that the differences of geopotential height (shaded) and wind speed (vector) at 500 hPa in the Asian Central Arid Zone including the Altai Moun- tains through calculating the circulation using NCEP/NCAR reanalysis data (Fig 11). As shown in Fig 11, the Altai Mountains were controlled by a cyclonic anomalies to their north- west and an anticyclonic anomalies to their southeast. This kind of atmospheric modes blocked the southward cold air and in turn provided favorable environment for water vapor transport via the westerlies from the North Atlantic, the Mediterranean and Caspian seas to

the Altai Mountains [56–57]. The horizontal moisture advection and wind convergence terms has a significant positive contribution to the wetting trend in the northwest China [58]. The southwesternly wind between the anomaly cyclone and the anomaly anticyclone driven the water vapor flux from the Mediterranean and Caspian sea into the Altai Mountains, which resulted in an increasing precipitation. Compared with the precipitation changes in sub-region 2, the larger increased precipitation in sub-region 1 and 3 could result from the effect of wind- ward slope [27]. The combination of complex topography and other local effects may be responsible for dif- ferent relationships between precipitation trend and elevation in the Altai Mountains [16–17]. Fig 11. Differences of geopotential height (shaded) and wind speed (vector) at 500 hPa between 1996–2016 and 1960–1995 (modified from Fig 12 in Xu et al. (2018)). The length and direction of arrows mean the flux and the direction of wind. https://doi.org/10.1371/journal.pone.0230196.g011 PLOS ONE Modern climate characters in the Altai Mountains PLOS ONE | https://doi.org/10.1371/journal.pone.0230196 March 17, 2020 11 / 15