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

Except Soloneshnoe, the precipitation at other remaining nine stations was featured by insig- nificant climbing trends (P>0.05). The increasing amplitude in Soloneshnoe was the most evi- dent and the largest with a rate of 11.27 mm/decade. The autumn precipitation exhibited insignificantly decreasing trends among eight stations in the northern Altai and in the eastern Altai. Insignificant trends were also observed in other stations with increasing rates spanning from 0.14 (Yalalt) to 4.71 (Habahe) mm/decade. In winter, only Zmeinogorsk, Mugur-Aksy and Kara-Tyurek showed decreasing trends with insignificant levels (P>0.05). All stations in the southern Altai Mountains had a significant increasing trend of precipitation in winter, while no significance was found among other stations. Overall, the Altai Mountains experi- enced a slightly wetting trend since 1970, especially in the southern Altai. Evolution of temperature and precipitation in sub-regions The monthly temperature in the Altai Mountains is characterized by the highest temperature in June-August and the lowest temperature in November-January during 1970–2015 (Fig 6A). The highest temperature (22.97˚C) was recorded in Zajsan and the lowest value (-28.78˚C) was in Kosh-Agach (Fig 6A). The three features of monthly precipitation were characterized in the Altai Mountains (Fig 6B). Firstly, the monthly precipitation was unimodal and was mainly concentrated in warm season (summer and autumn) with 55–84%. The related stations are Soloneshnoe, Kyzyl-Ozek, Yailu, Kara-Tyurek and Ust-Coksa. The MAP in these stations was

relatively high (average about 649.73 mm). Secondly, the feature of monthly precipitation was also unimodal, but the MAP was relatively low (average about 133.86 mm). The associated sta- tions are Mugur-Aksy, Kosh-Agach within Russia, three stations within Mongolia and Qinghe within China. Thirdly, being different to the former two features of precipitation, the distribu- tion of monthly precipitation was bimodal characterized by two peaks at April-September (50–68%) and at November- December (13–21%). The associated stations include Zmeino- gorsk, Habahe, Aletai, Fuyun, Semipalatinsk and Zajsan. Based on the features of monthly precipitation, the Altai Mountains was classified into three sub-regions: sub-region 1, 2 and 3 (Fig 1). The related trends of MAT and MAP among three sub-regions during 1970–2015 were presented in Fig 7. The result suggests that MAT all significantly increased among three sub-regions (Fig 7A). The most rapidly increased Fig 6. Variations of monthly temperature (a) and monthly precipitation (b) in the Altai Mountains during 1970–2015. https://doi.org/10.1371/journal.pone.0230196.g006 PLOS ONE Modern climate characters in the Altai Mountains PLOS ONE | https://doi.org/10.1371/journal.pone.0230196 March 17, 2020 7 / 15