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The semi-arid forest-steppe ecotone in the Khentii Mountains in Northern Mongolia is characterized by southerly exposed steppe slopes, shrublands in the floodplain of river valleys and northerly exposed taiga slopes. Here, the freshwater for the downstreaming agricultural, rural and mining sectors is generated. To gain insight into the main water-generating sources in mountainous river basins, we studied the actual evapotranspiration (ET) and its main influencing eco-hydrometeorological parameters at a steppe and a shrubland site during the growing season 2012. Latent ( LE) and sensible ( H) heat fluxes were measured using the Bowen ratio energy balance method, and the surface soil heat flux ( G) was determined with the PlateCal and GradCal approach. During water-stressed soil conditions at the steppe site, volumetric water content (VWC) values of 0.05 m m (−10 cm) resulted in significant limitations of the mean actual ET rates to 0.4 mm day. In contrast, high VWC with maxima of >0.4 m m and high mean actual ET rates >6.0 mm day were observed during water-unstressed soil conditions. As precipitation and change of stored soil moisture were approximately equal to actual ET, the contribution of freshwater from mountainous steppe within the forest-steppe ecotone can be neglected. At the shrubland site, which is underlain by a shallow aquifer system, VWC remained relatively constant with mean values of 0.4 m m (−10 cm). A multiple regression analysis indicated that actual ET, with mean rates of 2.3 mm day, was not significantly limited by precipitation and VWC, but by net radiation ( R) and air temperature. As precipitation exceeded total actual ET, shrub covered river floodplains can contribute to freshwater generation. [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]