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High topographic heterogeneity and complex mechanisms between the atmosphere and the ground create unique hydro-climatic processes over mountainous regions. Based on in situ observations, we present the spatial variability of ground surface temperature (GST) in the Khentii Mountains of northern Mongolia, which is situated at the southern fringe of the Eurasian permafrost zone. Changes in the hydrothermal regime of the active layer were investigated in association with changing climate and wildfire effects. The results reveal that the GST tends to increase continuously since 2011 in both thawing and freezing seasons, and varies significantly within a short horizontal distance, particularly during the thawing season. Extreme weather events, such as drought and heavy snowfall, amplify the increase in the ground temperature and deepen the seasonal thawing depth. The fire-induced loss in organic layer resulted in a greater heat penetration deeper into the ground and unbalanced the moisture distribution. Overall, the thawing depth is greater by >1.7 m under severely burned forest, compared to unburned forest. Given that about 30% of the boreal forest was affected by wildfire in the study area, the ground thermal regime changed considerably. The findings suggest that the combination of regional temperature rise and more frequent extreme weather and wildfire events in the region triggers permafrost degradation and alters the hydrothermal regime in the future. [ABSTRACT FROM AUTHOR]

Rapid warming has reduced seasonal snow cover and changed the hydrological regimes over many areas of the globe. Temperature increase cannot only stimulate snowmelt but also favors a shift of wintertime precipitation towards rainfall, especially in Western and Central Europe that has temperate and humid winters. We assume that the mid-season (January-February) instead of the end-season (March) snow is particularly sensitive to warming in the low mountain ranges of Europe, and increased rain-on-snow events are associated with the currently frequent winter floods. To validate this assumption, we simulated the snow water equivalent (SWE), rain-on-snow (ROS) events, evapotranspiration, runoff and percolation for the period 1961-2016 in Rhineland-Palatinate, southwestern Germany (< 820 m a.s.l.) using a distributed hydrological model (TRAIN). We analyzed the intra- and inter-annual variations of the simulated hydrological variables and the synchronous climate variables (air temperature and precipitation). Early spring (March) displayed the strongest warming and the January-February warming was less severe or insignificant. Precipitation amounts did not show significant trends. However, the snowpack in February experienced the most striking reductions, which is likely explained by both the highest susceptibility of snow to warming and the increased ROS occurrence in February since the early 1990s. An increment in runoff and percolation in the earlier winter is probably related to a combination of high temperatures and more rainfalls at that time. The expected changing climate towards warmer and wetter winters but drier springs will probably exacerbate the winter flooding and spring/summer drought risks in the future. [ABSTRACT FROM AUTHOR]

Knowledge of the snow cover dynamics in mountains of the semi-arid regions on Earth is essential for an improved understanding of the hydrological regime and for human water supply in a water scarce environment. In the semi-arid Sugnugur headwater catchment (in the Khentii Mountains, northern Mongolia), a spatial analysis of seasonal snow cover duration (SCD) was achieved on a 30 m grid by integrating the spatial resolution of Landsat-7, Landsat-8 and Sentinel-2A images with the daily temporal resolution of MODIS snow products (2000-2017). Validation was achieved using in situ measurements from winter field campaigns and spatially distributed surface temperature recordings. We found a mean increase of SCD with altitude at approximately +6 days/100m. However, no altitude-dependent changes in snow depth could be observed during the field campaigns. The southern exposed valley slopes are either snow free or covered by intermittent snow throughout the winter months due to high sublimation rates and prevailing wind. The estimated mean SCD ranges from 124 in the lower parts of the catchment to 226 days on the mountain peaks, with a mean underestimation of 12-13 days. Snow onset and melt dates exhibited large inter-annual variability, but no significant trend in the seasonal SCD was evident. Our method supports the better quantification of snow melt rates and thus water availability in this semi-arid environment. It can be applied to high-resolution snow mapping in similar mountainous regions. [ABSTRACT FROM AUTHOR]