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

Several uncertainties can influence the relationship of precipitation trend with elevation in mountainous regions over recent decades. Firstly, the long-term observed data of precipitation are extremely sparse at high elevations. For example, only two stations (Kara-Tyurek and Yalalt) are above 2000 m and no observed data is above 3000 m in the Altai Mountains. Mean- while, there is no available long-term precipitation data in the Altai Mountains within Kazakh- stan. The CRU (Climatic Research Unit) and GPCC (Global Precipitation Climatology Centre) data are able to describe the temporal-spatial variations of precipitation, but their uncertainties limit their applicability in the mountainous areas [59–60]. Secondly, there is a lack of consistency in the observation instruments and environments, such as vegetation changes, human grazing and relocation of stations because the Altai Mountains cover over four countries (China, Kazakhstan, Russia and Mongolia). The uncertainties would influence the relationships between climate and elevation to a certain extent, and the climate-elevation relationships should be observed and be investigated in future through (1) establishing more high-elevation stations and (2) combining three main methods including surface in-situ cli- mate observations, satellite remote-sensing data and high-resolution climatic modeling [2–5, 16]. Conclusions and implications The Altai Mountains experienced a rapid warming trend with a rate of 0.41˚C/decade and an insignificantly wetting trend at a rate of 4.82 mm/decade during 1970–2015. Being inconsis-

tent with the precipitation increasing trend with elevation in the Tianshan Mountains over recent decades [9, 16], the insignificantly increasing trend was showed in different elevations. The magnitude of temperature trend was negatively correlated with elevation in cold season (spring and winter), whereas that was positively correlated with elevation in warm season (summer and autumn). Additionally, the trends of precipitation magnitude with elevation in the Altai Mountains were complex. Two warning signs we should focus on. The first is that no obvious increasing precipitation poses a potential threat to the regional forest developments in middle elevations under the warming condition. The second is that no obvious increasing pre- cipitation directly affects storage of water resource in the Altai Mountains under the warming condition. In addition with significant mass loss of glaciers in the Altai Mountains [36–37, 61], a decreasing water storage may be a heavy threat to human survival through impacts on water availability. This urge us to take action to protect the safety of ecology and water resource in the Altai Mountains. Supporting information S1 Data. (RAR) Author Contributions Data curation: Yinbo Li, Mariia Andreeva, Lianlian Fan. Funding acquisition: Dongliang Zhang. Investigation: Dongliang Zhang, Yaoming Li, Min Tang. Project administration: Mariia Andreeva. Resources: Mariia Andreeva, Yaoming Li. Writing – original draft: Yinbo Li, Dongliang Zhang, Lianlian Fan, Min Tang. PLOS ONE Modern climate characters in the Altai Mountains

PLOS ONE | https://doi.org/10.1371/journal.pone.0230196 March 17, 2020 12 / 15