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The relationship between reservoirs and naturally formed lakes in Mongolia has not been previously studied. This research explores potential future environmental impacts, both positive and negative, in western Mongolia. The study employs morphological analysis (MA), normalised difference water index (NDWI), volume analysis and statistical analysis of water. In the case of Airag Lake and an artificially created lake, temporal changes in lake surface area and volume exhibit inverse trends. The correlation between changes in lake area over time is highly negative ( = −0.96, < 0.01 for the surface area), which is attributed to a decrease in Airag Lake’s area and volume during the lake water accumulation period from 2007 to 2011 and countered by an increase in Gegeen Lake’s area and volume. Conversely, the surface area of Khyargas Lake shows a strong positive correlation ( = 0.94, < 0.0001) with Airag Lake’s area and a strong negative correlation ( = –0.88, < 0.0001) with Gegeen Lake’s area during the period from 2007 to 2021. Based on satellite data, our findings suggest a negative relationship between changes in lake surface area and volume, indicating recent significant human impacts on lake water balance. This research explores the implications of hydropower dams and reservoirs in the region, as well as environmental concerns within the context of power production.

Ugii Lake is a freshwater lake located in the steppe region of Mongolia and is an important breeding and staging area for a wide variety of waterfowl. Remote sensing and geographic information system techniques were used to estimate fluctuations in the surface area and water balance of Ugii Lake. To estimate the changes in lake water balance, lake water fluctuations should be analyzed using the most accurate methods. A different water extraction technique was applied, and the results were compared with field surveys conducted in May, July, and September 2020. The lake surface area using both NDWI and MNDWI-1 showed a strong, positive correlation (R=0.93, R=0.94, p < 0.01) with the water level of Ugii Lake. A topographic map of Ugii Lake was provided by the project (P2018-3568) conducted in August 2019 and used to estimate the volume of Ugii Lake in ArcGIS 10.1. This result was consistent with that of a previous study by JICA in 2005. Finally, the water balance of Ugii Lake was estimated, and the results proved that the influence of both surface and groundwater on Ugii Lake are valuable parameters, which are completely dependent on hydrological regime changes mostly due to local climate change in steppe regions. This study provides valuable insight into the most suitable water extraction methods for lakes in semi-arid steppe regions in Mongolia.

Land cover and vegetation in Lake Baikal basin (LBB) are considered to be highly susceptible to climate change. However, there is less information on the change trends in both climate and land cover in LBB and thus less understanding of the watershed sensitivity and adaptability to climate change. Here we identified the spatial and temporal patterns of changes in climate (from 1979 to 2016), land cover, and vegetation (from 2000 to 2010) in the LBB. During the past 40 years, there was a little increase in precipitation while air temperature has increased by 1.4 °C. During the past 10 years, land cover has changed significantly. Herein grassland, water bodies, permanent snow, and ice decreased by 485.40 km2, 161.55 km2 and 2.83 km2, respectively. However, forest and wetland increased by 111.40 km2 and 202.90 km2, respectively. About 83.67 km2 area of water bodies has been converted into the wetland. Also, there was a significant change in Normalized Difference Vegetation Index (NDVI), the NDVI maximum value was 1 in 2000, decreased to 0.9 in 2010. Evidently, it was in the mountainous areas and in the river basin that the vegetation shifted. Our findings have implications for predicting the safety of water resources and water eco-environment in LBB under global change.

Data on the origin and morphology of lake depressions caused by volcanism are scarce in Mongolia. Previous studies focused on climate change patterns based on Terkhiin Tsagaan Lake sediment. We present a result of existing reconstructions of lake depression development and changes in the hydrology system during the Khorgo volcanic activation and the Holocene environmental change. A depression of the Terkhiin Tsagaan Lake is formed by a lava flow barrier from the Khorgo volcano. However, the Khorgo volcanic eruption and the lake depression that could shape a large lake have arisen instead from a fault. The morphometric analysis and field measurements indicate that the derivation of the Terkhiin Tsagaan Lake depression and Khorgo volcano may have evolved from movement on a sinistral strike-slip fault, which is about 70 km long. The southern mountains and rivers were displaced from northwest to southeast along the Terkh Fault. The offset along Terkh Fault is 4.02–5.28 km in the depression of the Terkhiin Tsagaan Lake. After movement, a wide valley of the Terkh River developed in the present landscape. The active Khorgo Volcano formed along the Khorgo Fault. The Terkhiin Tsagaan Lake is formed by blocked water from the Paleo-Terkh River after lava damming from the Khorgo Volcano. The initial paleo-lake area was about 195.7 km2, which was three times larger than the modern lake. The current water volume of the Terkhiin Tsagaan Lake is 0.351 km3 while the volume of the paleo-lake was 2.248 km3. Based on this volume indicator the paleo-lake was 6.4 times larger than the current lake. Overflowing water from the lake depression formed the Suman River by a drying canyon through the lava plateau, but the canyon is along the Terkh Fault. Changes in the water volume of Terkhiin Tsagaan Lake and erosion of Suman River canyon are inversely related to each other. We present the morphometric relationships between the lava plateau of Khorgo Volcano and development of Terkhiin Tsagaan Lake depression.

The Tuul River Basin is the most important socioeconomic and political base area of Mongolia. Therefore, studying the interrelationships between changes in the ecohydrological processes of this basin and its land cover is of great importance for maintaining sustainability and the environment. This study investigated the annual average air temperature, total annual precipitation, and river discharge variability, and land cover changes at selected stations of the basin by using the hydrometeorological analysis, satellite analysis, and land cover determination statistical analysis. During the study period, the average annual air temperature rose from −1.5 °C to +0.3 °C (1.8 °C 361 °C). The average annual precipitation exhibits relatively low change during this period. River discharge varied during the study period. A significant decreasing trend in river discharge was observed at the Terelj (φ = −2.72) and Ulaanbaatar (φ = −5.63) stations, whereas the other stations, Altanbulag, Lun, and Orkhontuul, showed a significant increasing trend. During the study period, changes in land cover were directly related to main hydrometeorological parameters. Between 2000 and 2020, the amount of grassland decreased by 319.67 km2, while the area of water bodies increased by 28.36 km2. In the study area, mainly water bodies and sensitive areas of the land cover types were changed due to changes in precipitation. Studies in the arid and semiarid regions of Central Asia show that changes of ecohydrological processes have a significant impact on land cover changes.

Mongolia’s Selenga sub-basin of the Lake Baikal basin is spatially extensive, with pronounced environmental gradients driven primarily by precipitation and air temperature on broad scales. Therefore, it is an ideal region to examine the dynamics of the climate and the hydrological system. This study investigated the annual precipitation, air temperature, and river discharge variability at five selected stations of the sub-basin by using Mann-Kendall (MK), Innovative trend analysis method (ITAM), and Sen’s slope estimator test. The result showed that the trend of annual precipitation was slightly increasing in Ulaanbaatar (Z = 0.71), Erdenet (Z = 0.13), and Tsetserleg (Z = 0.26) stations. Whereas Murun (Z = 2.45) and Sukhbaatar (Z = 1.06) stations showed a significant increasing trend. And also, the trend of annual air temperature in Ulaanbaatar (Z = 5.88), Erdenet (Z = 3.87), Tsetserleg (Z = 4.38), Murun (Z = 4.77), and Sukhbaatar (Z = 2.85) was sharply increased. The average air temperature has significantly increased by 1.4 °C in the past 38 years. This is very high in the semi-arid zone of central Asia. The river discharge showed a significantly decreasing trend during the study period years. It has been apparent since 1995. The findings of this paper could help researchers to understand the annual variability of precipitation, air temperature, and river discharge over the study region and, therefore, become a foundation for further studies.

The Ugii Nuur Lake is not only one of the small hydrologically closed lakes located in the Orkhon River Basin in Central Mongolia but also the most vulnerable area for global climate change. Therefore, this study aims to investigate the impacts of recent global climate change on the water surface area. The data we analyzed were various measured hydro-meteorological variables of the lake basin and the lake surface area, which was estimated from Landsat series satellite data from 1986 to 2018. The methods we used were Mann-Kendall (MK), Innovative trend analysis method (ITAM), Sen’s slope estimator test, correlation, and regression analysis. The variation of lake water surface area has a strong positive correlation with the change of the lake water level (r = 0.95). The Mann-Kendall trend analysis has indicated that under a significant decrease in total annual precipitation ( Z   = −0.902) and inflow river discharge ( Z   = −5.392) and a considerable increase in total annual evaporation ( Z = 4.385) and annual average air temperature ( Z   = 4.595), the surface area of the Ugii Nuur Lake has decreased sharply ( Z = −6.021). The total annual evaporation (r = −0.64) and inflow river discharge (r = 0.67) were the essential hydro-meteorological factors affecting the surface area of the Ugii Nuur Lake. The lake surface area decreased by 13.5% in 2018 compared with 1986. In the near future, it is vital to conduct scientific studies considering the volume of lake water, groundwater, and the anthropogenic impact.

This study used the Innovative trend analysis method, Mann-Kendall, and Sen’s slope estimator test to investigate the mean annual precipitation, annual mean air temperature, and river discharge at selected stations of the sub-basin. The results showed that the trend of annual precipitation trend was significantly increased in Nizhneangarsk station (ф = 0.88 and Z = –0.64) and Bolshoe Goloustnoe (ф = 0.24 and Z = 1.14*) whereas, the other stations showed a decreasing trend. The most decreasing trend was observed in the Ust Barguzin station (ф = –0.68, Z = –2.38**, and β = –0.95). The average air temperature has increased by 1.7°C from 1970 to 2019. All stations showed an increasing trend of annual air temperature during the study period. The most increasing condition was observed in the Ulan Ude station (ф = 9.20***, Z = 7.78***, and β = 0.04). The river discharge showed an increasing trend in Utulik River, Upper Angara River, and Barguzin rivers. The most decreasing is in the Selenga river gauge station (ф = –2.25**, Z = –2.16**, and β = –2.96**). The warming rates in the Selenga river sub-basin of the study area were higher than those in the other four sub-basins and the global climate change more affects the semi-arid region.

Arid and semi-arid regions are the first to be affected by hydro-climatic changes. The Great Lakes Depression Basin in western Mongolia is the most notable example of such a region. Therefore, analyzing hydro-climatic changes in the Great Lakes Depression region is essential for future climate, hydrological, eco-hydrological processes, and ecosystem studies in similar areas and basins. In this study, Mann–Kendall (MK), innovative trend analysis method (ITAM), and Sen's slope estimator test (SSET) were used to determine the interrelationship between climate and river discharge changes and lake water level changes through statistical analysis. During the last 30 years, the air temperature has increased by 1.2 °C (Z = 1.16). Total annual precipitation decreased by 23.44 mm, resulting in 134.16 mm (Z = −0.79). The river discharge of the major rivers, such as Khovd River (Z = −3.51) and Zavkhan River (Z = −6.01), has significantly decreased. In Uvs (Z = 0.30) and Khyargas (Z = 2.03) lakes, the water level has also dropped. This study confirms that the increase in air temperature in the depression area of the Great Lakes reduces the amount of precipitation, and the decrease in precipitation affects the decrease in river discharge, which further affects the water level of the inflowing lakes.