Lake Water Storage Changes Research Articles

Lake water storage changes and their cause analysis in Mongolia

Lake is an important water resources in Mongolia, which has undergone a large variation in past decades. However, it is still challenging to monitor long-term changes in lake water storage (LWS) due to the lack of lake level monitoring and long-term satellite altimetry data for Mongolian lakes. According to the Advanced Land Observing Satellite Digital Elevation Model (ALOS DEM) and the Joint Research Centre (JRC) dataset, we estimated the LWS changes of 55 Mongolian lakes (> 10 km2) from 1991 to 2020. The results showed that the LWS increased by 40.24 km3 from 1991 to 1997, especially for northwestern Mongolia with 31.47 km3. However, the LWS decreased by 32.44 km3 from 1998 to 2010, and the lakes in the northwestern and southern decreased by 20.24 km3 (62%) and 7.38 km3 (23%), respectively, and then the LWS continued to decrease by 10.22 km3 from 2011 to 2020. The precipitation was the primary cause of lake change, which could explain 45.13% of LWS change based on Generalized Linear Model, followed by temperature (26.33%) and irrigated area (16.72%). Analyzing the changing characteristic and driving mechanisms of LWS can provide a scientific basis for local water resources management and planning.

Mapping inundated bathymetry for estimating lake water storage changes from SRTM DEM: A global investigation

Lake water budgets are sensitive to climate change and human activities and have been undergoing rapid changes worldwide over the past few decades. Satellite altimeters greatly promote the large-scale monitoring of lake level and storage variations. However, limited spatiotemporal coverage of the existing individual altimeters prevents long-term and spatially seamless observations on global lakes. These limitations are partially surmounted by the gridded digital elevation model (DEM) data, which can facilitate spatially contiguous measurements of lake bathymetry exposed at the low-level period. The high-resolution SRTM DEM has been widely used for estimating lake level variations due to its early collection time and reliable data quality, while how many lakes worldwide and to what extent of the newly inundated areas can be monitored based on SRTM DEM remains unexplored. Here, we conduct a quasi-global investigation of SRTM DEM regarding its capability of mapping inundated-area bathymetry and estimating lake storage variations. After generating a global-scale lake inventory (122,444 lakes below 60°N, >1 km2) representing the maximum water inundation extents between 1984 and 2020, the feasibility of mapping lake inundated-area bathymetry was evaluated by comparing the maximum inundated area with the waterbody extent derived from SRTM DEM and analyzing the characteristics of interannual and seasonal variability of each lake. Results show that the maximum exposed lake bathymetries from the SRTM DEM data cover an area of 372,986 km2, accounting for 15.95% of the maximum water area of our investigated lakes. Climate-driven lake expansions or human-induced reservoir impoundments after 2000 (the SRTM mission period) are the main contributors to the higher availability of SRTM DEM-based bathymetry mapping on the Tibetan Plateau, India, eastern China, and Amazon Plains. As the newly launched Surface Water and Ocean Topography (SWOT) mission is anticipated to monitor lake water budget variation at an unprecedented resolution, this study provides a base map for supplementing inundated bathymetry information. The joint use of SRTM and SWOT-based observations will extend the time and space extents of lake-level measurements, thereby enhancing our understanding of lake dynamics at a longer timescale.

Lake Evaporation and Its Effects on Basin Evapotranspiration and Lake Water Storage on the Inner Tibetan Plateau

AbstractEffects of lake evaporation (EW) on basin evapotranspiration (ETB) and lake water storage change (LWSC) at lake‐basin scale have never been reported for most basins on the inner Tibetan Plateau (IB). In this study, EW of 118 large lakes in 95 closed lake‐basins were estimated, and its effects on ETB and LWSC over 2001–2018 were examined using a derivative‐guided framework from the aspects of EW amount, rate, trend slope and inter‐annual variability. We found that EW amount has a high effect (17%) on regional ETB amount compared to the average lake area ratio (α) (∼5%), and the effect has increased significantly (2%/10 a). The spatial pattern of the effect is mainly controlled by α, and the increasing trend of α (0.6%/10 a) also dominated the increasing trend in regional ETB rate (0.30 mm/a) though with large spatial heterogeneity. Variance in α and EW rate have a minor effect (∼3%) on ETB variance, especially for the basins with lower α. The combination of quasi lake inflow (RL, 41%) and lake surface precipitation (PW, 16%) offset the depletion of EW (−43%), resulting in the surplus of regional lake water (LWSC > 0). The increase in EW mount, which is mainly from lake area expansion (90%), caused a decreasing trend in LWSC (i.e., slower growth rate) with a contribution of −59%. This suggests a negative feedback between lake area expansion and EW amount in the IB, and the feedback may continue with the predicted area increases.

Long-Term Change of Lake Water Storage and Its Response to Climate Change for Typical Lakes in Arid Xinjiang, China

Lakes play a role as the sentinel of climate change. Surrounded by vast expanses of barren land with limited infrastructure, there is also a lack of knowledge about the dynamics of dryland lakes. The change of lake area can be effectively monitored by remote sensing, and multi-source satellite altimetry datasets provide the possibility to obtain long-term lake water level data. Using the Global Surface Water Monthly Historical dataset and altimetry water level dataset (Hydroweb), we reconstructed a time series of lake water storage changes in Xinjiang, Northwestern China, by establishing the empirical models based on the statistical relationship between the surface area and water level of each lake. We further explored lake response to climate change. The results show that the storage of water at Ayakkum Lake, Aqqikkol Lake and Aksayquin Lake have been undergoing an obvious expanding trend from 2000 to 2020, at a rate of 3.59×108m3/a, 9.43×108m3/a and 0.44×108m3/a, respectively. In the plain and transition zone, Ulungur Lake showed an upward tendency (0.413×108m3/a) in water storage, while Manas Lake and Bosten Lake experienced shrinkage with descending rates of −0.1×108m3/a and −0.86×108m3/a. Temperature changes significantly affect the lake water storage on plateaus, especially those lakes supplied with a large proportion of glacial meltwater. Precipitation is a key factor for changes of lake storage in the plain and transition zones. Meanwhile, extreme weather and man-made factors also play crucial roles. To reduce the risk of flood and drought disasters, rational regulation of water resources is required, and a large-scale integrated catchment management plan can avoid inadvertent trade-offs. This research provides a new perspective for lake water storage inversion, as well as data support for water resources management in arid areas including Xinjiang.

Continuous Intra-Annual Changes of Lake Water Level and Water Storage from 2000 to 2018 on the Tibetan Plateau

There is a large amount of lakes on the Tibetan Plateau (TP), which are very sensitive to climate change. Understanding the characteristics and driving mechanisms of lake change are crucial for understanding climate change and the effective use of water resources. Previous studies have mainly focused on inter-annual lake variation, but the continuous and long-term intra-annual variation of lakes on the TP remains unclear. To address this gap, we used the global surface water (GSW) dataset and the Shuttle Radar Topography Mission (SRTM) DEM to estimate the water level and storage changes on the TP. The results indicated that the average annual minimum lake water level (LWLmin) and the average annual maximum lake water level (LWLmax) increased by 3.09 ± 0.18 m (0.16 ± 0.01 m/yr) and 3.69 ± 0.12 m (0.19 ± 0.01 m/yr) from 2000 to 2018, respectively, and the largest change of LWLmin and LWLmax occurred in 2002–2003 (0.45 m) and 2001–2002 (0.39 m), respectively. Meanwhile, the annual minimum lake water storage change (LWSCmin) and annual maximum lake water storage change (LWSCmax) were 125.34 ± 6.79 Gt (6.60 ± 0.36 Gt/yr) and 158.07 ± 4.52 Gt (8.32 ± 0.24 Gt/yr) from 2000 to 2018, and the largest changes of LWSCmin and LWSCmax occurred in the periods of 2002–2003 (17.67 Gt) and 2015–2016 (17.51 Gt), respectively. The average intra-year changes of lake water level (LWLCintra-year) and the average intra-year changes of lake water storage (LWSCintra-year) were 0.98 ± 0.23 m and 40.19 ± 10.67 Gt, respectively, and the largest change in both LWLCintra-year (1.44 m) and LWSCintra-year (62.46 Gt) occurred in 2018. The overall trend of lakes on the TP was that of expansion, where the LWLC and LWSC in the central and northern parts of the TP was much faster than that in other regions, while the lakes in the southern part of the TP were shrinking, with decreasing LWLC and LWSC. Increased precipitation was found to be the primary meteorological factor affecting lake expansion, and while increasing glacial meltwater also had an important influence on the LWSC, the variation of evaporation only had a little influence on lake change.

Unravelling lake water storage change in Central Asia: Rapid decrease in tail-end lakes and increasing risks to water supply

There are extensive and fragile mountain-oasis-desert ecosystems in Central Asia. Lakes are not only the most important water resources in arid Central Asia, but also important resources for maintaining the unique ecosystem of the region. As most lakes in Central Asia lack in situ monitoring data, and satellite altimetry records are relatively short-term, the continuous long-term monitoring of lake water storage change (LWSC) in Central Asia is inadequate. To this end, Shuttle Radar Topography Mission digital elevation model data were used in conjunction with all available Landsat images to construct an empirical model of area–elevation–storage changes and estimate the maximum LWSC (maxLWSC) and minimum LWSC (minLWSC) of 9,619 lakes (watershed area > 10 km2) in Central Asia from 1990 to 2020. Subsequently, the random forest (RF) algorithm was used to quantitatively evaluate the associations among climate change, human activities, and LWSC. It was revealed that maxLWSC and minLWSC decreased by 27.94 and 144.21 Gt, respectively. The results also revealed that LWSC varied by elevation, whereby lakes below 3,500 m shrunk and those above 3,500 m expanded. The RF findings demonstrated that human activities are more important than climate change for LWSC in Central Asia. Up to 96 % of LWSC can be explained by human activities. This study comprehensively evaluates the characteristics of LWSC in Central Asia, providing the latest data to help alleviate the contradiction between water supply and demand in Central Asia and resolve cross-border water resource disputes, so as to realize the protection of fragile regional ecosystems.

Simulation of the Water Storage Capacity of Siling Co Lake on the Tibetan Plateau and Its Hydrological Response to Climate Change

Due to their special geographical locations and environments, plateau lakes play a key role in maintaining regional water balance, but lake water storage changes are upsetting this balance. Based on data from lakes on the Tibetan Plateau (TP), this study used the Spatial Processes in Hydrology (SPHY) model to simulate the runoff process in the Siling Co basin from 2000 to 2016 and estimated the changes in water storage of Siling Co and the contribution of each component of runoff into the lake. The results showed that the water storage capacity of Siling Co has increased by 1.2 billion m3/yr, and the lake area continues to expand; declines in precipitation have significantly reduced baseflow (BF), rainfall runoff (RR), and snow runoff (SR), while temperature increases have raised glacier runoff (GR). The simulated average runoff showed that BF, GF, RR, and SR contribute 24%, 22%, 16%, and 38%, respectively, of the flow into Siling Co. Based on hypothetical climate change scenarios and two Shared Socioeconomic Pathways (SSP1-2.6 and SSP3-7.0) from the MRI-ESM2-0 GCMs, this study estimated that a 10% increase in precipitation could lead to a 28% increase in total runoff, while a 1 °C increase in temperature could lead to a 10% decrease in runoff. The average runoff depth of the basin is expected to increase by 30–39 mm, since the temperature and precipitation may increase significantly from 2020 to 2050. The intensification of glacial melting caused by the increase in temperature continues, posing a greater challenge to many water resources management problems caused by the expansion of lakes.

Response of terrestrial water storage and its change to climate change in the endorheic Tibetan Plateau

Terrestrial water storage (TWS) and its change (TWSC) are extremely sensitive to climate change, and are good indicators of the response of the hydrological system to climate change in the Tibetan Plateau (TP). However, long-term variation in TWS and its components, as well as contributions of these component changes to TWSC, are still not well documented. In this study, we extended monthly TWS anomaly (TWSA) and TWSC from 1989 to 2019 using the random forest (RF) method, analyzed the long-term contribution rates of each component change to TWSC using a mass balance approach, and compared them with the rates estimated by the RF method. Our major findings are: (1) the warming and wetting trend in the entire analysis period (PA) and in the pre-mutation period (P1) was slowed down or even reversed in the post-mutation period (P2), which was caused mainly by the decrease in temperature and precipitation in the north-eastern Inner Basin (IB) and southern Qaidam Basin (QB); (2) the RF method is capable of estimating monthly TWSA and TWSC (0.872 ≤ R2 ≤ 0.957 in training data, 0.528 ≤ R2 ≤ 0.860 in test data). Variable selection has an important impact on the method, and TWSC can be used as an alternative when TWSA estimate is poor; (3) Significant annual TWSA increase (2.20 mm/a, P < 0.05) in the IB during PA comes from a higher increase during P2 (3.62 mm/a, P < 0.05) and a small variation during P1 (−0.65 m/a, P > 0.1). Spatially, the increase is attributed to the higher increase trends (> 4.50 mm/a, P < 0.05) in north-eastern IB during PA and P2, and slight decrease in western and southern IB during PA. The spatial and temporal heterogeneity was mainly caused by the differences in precipitation amount, glacier proportions, and permafrost types. (4) During PA, TWSC in the IB was mainly determined by lake water storage change (LWSC) with a contribution rate of 62 %, while in the QB it was mainly determined by soil water change (−43 %), and LWSC had a contribution rate of −27 %. LWSC impact on TWSC was more significant in the IB, especially in the southeastern sub-regions with regional water storage surplus (TWSC > 0). The overall increase in water storages and fluxes, and exchanges imply an intensified hydrologic cycle in the region.

Lake Water Storage Changes in Northeast Hoh Xil Observed by Cryosat-2 and Landsat-5/7/8: Impact of the Outburst of Zhuonai Lake in 2011

The outburst of Zhuonai Lake (ZL) in 2011 changed the local hydro-ecological system in northeast Hoh Xil (HX). This study focuses on the impact of the outburst on lake water storage changes (LWSCs) of four lakes in this region. Monthly LWSC from 2009 to 2016 were constructed using Landsat and Cryosat-2 data. We determined and validated lake levels and areas derived from Cryosat-2 and Landsat data, respectively. The two satellite-derived sequences were merged by interpolation to compute LWSC, based on the level-area curve derived from the digital elevation model (DEM). Results reveal the apparent impact of the outburst on the hydrological system. Before the outburst, water volumes in all four lakes continuously grew from January 2009 to September 2011, with a total increase of 1.49 ± 0.08 Gt. Most increased water was distributed in ZL and Kusai Lake (KL). The LWSC of each lake was strongly correlated (>0.9) with those of the whole basin. However, from October 2011 to December 2016, there was no ascending trend in LWSC of the three upper stream lakes, although the water volume in the basin was still increasing. More than 80% of the increased water flowed into Salt Lake (SL). Only the LWSC of SL kept a high correlation (0.91) with those of the whole basin.

Seasonal Seismicity in the Lake Biwa Region of Central Japan Moderately Modulated by Lake Water Storage Changes

AbstractSeasonal seismicity in Japan has been observed and attributed to variations induced by hydrological loading, as well as atmospheric and pore‐fluid pressure. We examine the seasonal variations of crustal (&lt;15 km depth) and low magnitude (M &lt; 4.5) earthquakes in central Japan near the Biwako‐Seigan Fault Zone (BSFZ), and analyze their correlation with the annual hydrological cycle of nearby Lake Biwa, the largest freshwater lake in Japan. The 2002–2018 lake water storage is estimated using water‐level gauge and satellite altimetry data. Regional surface mass loading from soil moisture and snow predicted by the Global Land Data Assimilation System is used to augment the lake mass variation. We compute the stress and stressing‐rate changes induced by the surface mass loading from lake storage, snow, and soil moisture at seismogenic depth (10 km) along the BSFZ using a finite element model incorporating a 3D Earth structure. The results show that seasonal surface mass loading generates 1–5 kPa peak‐to‐peak Coulomb stress change and 2.5–15 kPa/year stressing‐rate variations on the fault segments along the BSFZ. Two of the four fault segments present significant correlation between local seismicity rate and loading‐derived stress and/or stressing rate changes. Among the hydrological load components, lake water, snow, and soil moisture exhibit different annual phases, and the lake water storage dominates the total annual stress changes. Our analysis indicates that seasonal surface hydrological loads, especially lake water variations, modulate the seismicity rate along the BSFZ in central Japan.

Constraining the contribution of glacier mass balance to the Tibetan lake growth in the early 21st century

The Tibetan Plateau (TP) hosts numerous glaciers and lakes which are critical natural water reserves but highly vulnerable to changing climate. In contrast to general drying trends in global endorheic basins in recent decades, the widespread lake expansions across the endorheic TP stand out as a puzzling “anomaly”. To quantify the contribution of glacier mass changes to lake expansion at fine basin-scale details, we compute spatially resolved estimation of mass change in both glaciers and lakes across the endorheic TP between 2000 and 2010/14 based on multi-mission remote sensing observations. Our glacier mass balance estimates were based on the differences between the newly released global TanDEM-X DEM and the historical SRTM-C DEM, which provide nearly complete coverage (98%) of the glacierized area on the endorheic TP. We provide lake water storage changes of all lakes >1 km2 on the inner TP. These estimates reveal that the massive lake water increase (9.44 ± 1.43 Gt yr−1) was essentially not from the mass loss of glaciers which represents only about 4.7 ± 8.8% of the lake water change (0.44 ± 0.80 Gt yr−1). The relationship in individual basins was, however, highly heterogeneous. About 20% of total lake storage gain had no causality with glacier feeding. In comparison, for 28% of lake water surplus, mainly in the northwestern TP, the positive glacier mass balance infers that glaciers retained some precipitation surplus that could otherwise have been drained to downstream lakes. For the other 52% of lake storage gain, mostly in southern and eastern regions, the glacier mass loss varied among the basins with limited contributing levels (mostly <20%). Our analyses highlight remarkable spatial and temporal variabilities in lake/glacier changes on the endoreic TP and contribute to a better understanding of the role of glaciers in the recent Tibetan lake growth and the impact of climate change on the two types of water reserves.

Lake water storage change estimation and its linkage with terrestrial water storage change in the northeastern Tibetan Plateau

Lake water storage change estimation and its linkage with terrestrial water storage change in the northeastern Tibetan Plateau

Spatial Difference of Terrestrial Water Storage Change and Lake Water Storage Change in the Inner Tibetan Plateau

Water resources are rich on the Tibetan Plateau, with large amounts of glaciers, lakes, and permafrost. Terrestrial water storage (TWS) on the Tibetan Plateau has experienced a significant change in recent decades. However, there is a lack of research about the spatial difference between TWSC and lake water storage change (LWSC), which is helpful to understand the response of water storage to climate change. In this study, we estimate the change in TWS, lake water storage (LWS), soil moisture, and permafrost, respectively, according to satellite and model data during 2005−2013 in the inner Tibetan Plateau and glacial meltwater from previous literature. The results indicate a sizeable spatial difference between TWSC and LWSC. LWSC was mainly concentrated in the northeastern part (18.71 ± 1.35 Gt, 37.7% of the total) and southeastern part (22.68 ± 1.63 Gt, 45.6% of the total), but the increased TWS was mainly in the northeastern region (region B, 18.96 ± 1.26 Gt, 57%). Based on mass balance, LWSC was the primary cause of TWSC for the entire inner Tibetan Plateau. However, the TWS of the southeastern part increased by 3.97 ± 2.5 Gt, but LWS had increased by 22.68 ± 1.63 Gt, and groundwater had lost 16.91 ± 7.26 Gt. The increased TWS in the northeastern region was equivalent to the increased LWS, and groundwater had increased by 4.47 ± 4.87 Gt. Still, LWS only increased by 2.89 ± 0.21 Gt in the central part, and the increase in groundwater was the primary cause of TWSC. These results suggest that the primary cause of increased TWS shows a sizeable spatial difference. According to the water balance, an increase in precipitation was the primary cause of lake expansion for the entire inner Tibetan Plateau, which contributed 73% (36.28 Gt) to lake expansion (49.69 ± 3.58 Gt), and both glacial meltwater and permafrost degradation was 13.5%.

Remote Detection of Varying Water Storage in Relation to Surfacial Temperature of Aral Sea

Lake monitoring by remote sensing is of significant importance to understanding the lake and ambient ecological and environmental processes. In particular, whether lake water storage variation could predict lake surfacial temperature or vice versa has long fascinated the research community, in that it would greatly benefit the monitoring missions and scientific interpretation of the lake change processes. This study attempted to remotely detect the dynamics of the Aral Sea and pursue the relationships between varying lake water storage attributes and surface water temperature by using MODIS LST (Moderate-resolution Imaging Spectroradiometer Land Surface Temperature) 8-day composite products, satellite altimeter data, and actual meteorological measurements. Their associations with lake Surface Water Temperatures (SWT) were then analyzed. Results showed the lake water surface areas and elevations of the North Aral Sea tended to increasing trend from 2001 (2793.0 km2, 13.6 m) to 2015 (6997.8 km2, 15.9 m), while those of the South Aral Sea showed a decreasing trend during 2001 (20 434.6 km2, 3.9 m) and 2015 (3256.1 km2, 0.9 m). In addition, the annual daytime and nighttime lake SWT both decreased in the North Aral Sea, while only the daytime SWT in the South Aral Sea exhibited an increase, indicating a rising deviation of diurnal temperatures in the South Aral Sea during the past 15 yr. Moreover, a lower correlation was found between variations in the daytime SWT and storage capacity in the South Aral Sea (R2 = 0.33; P < 0.05), no fair correlations were tested between lake water storage and daytime SWT in the North Aral Sea nor between lake water storage and nighttime SWT in either part of the sea. These results implied that climate change, if any at least during the research period, has no significant effects on lake dynamics over the two sectors of the Aral Sea with anthropogenic disturbances. However, climate change and human activities may overlap to explain complex consequences in the lake storage variations. Our results may provide a reference for monitoring the spatiotemporal variations of lakes, increasing understanding of the lake water storage changes in relation to the lake SWT, which may benefit the ecological management of the Aral Sea region, in the effort to face the likely threats from climate change and human activities to the region.

Difference and cause analysis of water storage changes for glacier-fed and non-glacier-fed lakes on the Tibetan Plateau.

Lakes on the Tibetan Plateau are very sensitive to climate change and have expanded rapidly in recent decades. In this study, lake water storage change (LWSC) of 150 lakes since 1976 was estimated based on multi-temporal Landsat images and Shuttle Radar Topography Mission data. The lakes were then separated into glacier-fed and non-glacier-fed lakes based on the second Chinese glacier inventory and basin boundaries. The results indicate that most lakes had a shrinking trend and total water storage decreased by 5.53 ± 0.4 km3 from 1976 to 1990; however, most lakes expanded and increased in total water storage by 110.15 ± 7.93 km3 from 1990 to 2013. The water storage increase in glacier-fed lakes was 84% of the total increase in water storage from 1990 to 2013. An analysis of the relationship between the lakes and climate indicators suggests that both precipitation and glacial meltwater were the most important factors in lake change, in contrast, changes in evaporation had a limited influence on lake level and volume changes. Based on an assumption of similar precipitation and evaporation across neighbouring closed basins, we compared differences in LWSC between glacier-fed and non-glacier-fed lakes to analyze the cause of lake change. Our results suggest that less precipitation was the primary cause for lake contractions from 1976 to 1990. Glacial meltwater contributed at least 43.5%, 46.4% and 58.7% to the total increased water storage for the periods 1990-2000, 2000-2005 and 2005-2013, respectively. The results further suggest that increasing glacial meltwater had a contribution to lake expansion equivalent to that of precipitation-evaporation during 1990-2013.

Global open-access DEM performances in Earth's most rugged region High Mountain Asia: A multi-level assessment

Over the past decades, climate change has exerted pronounced influences on the cryo-hydrologic environments in High Mountain Asia (HMA). Digital elevation models (DEMs) are one of the critical datasets required in many hydrology- and cryosphere-related studies in HMA, which include estimations of glacier mass balances and lake water storage changes and hydrological runoff modelling. Several global or near-global coverage DEMs (e.g. SRTM and ASTER missions) have been widely utilized for such studies. However, a comprehensive assessment of the quality of these DEMs, particularly over the high-relief HMA area, is still lacking. This study investigated the performances of seven public freely-accessed DEM datasets (ASTER GDEM V2, SRTM-3 V4.1 DEM, SRTM-1 DEM, AW3D30 DEM, VFP-DEM, MERIT DEM, Seamless SRTM-1 DEM) over the HMA region by referring to high-accuracy elevation data from ICESat altimetry. We also provided an additional detailed assessment for typical lake basins and extremely rugged areas in the Himalayas by using available global positioning system (GPS) measurements and gridded SETSM DEM raster data. Results show that AW3D30 exhibits the highest accuracy in HMA land areas among these datasets. The accuracy of all studied DEMs demonstrates high spatial variation, which shows the strongest relationship with slope among several topographical factors, such as elevation and aspect. Over these rugged terrains with a large slope, such as the Hengduan Mountains and Himalayas, the vertical accuracy is relatively low in all investigated DEMs. We established empirical models for fitting the relationship between DEM vertical error and mean slope, which can be used to estimate the average elevation errors for any given local or basin-scale DEM grids. In addition, this study identified regions with anomalous elevation data in each dataset caused by the imperfect void-filling processing scheme. In sum, the 3-arc-second MERIT DEM is judged to be relatively dependable for HMA which not only achieves good performances in statistical error values but also retains few void-filling anomalies. The 1-arc-second AW3D30 could be the most promising product over HMA with its high spatial resolution and accuracy, although some void-filling anomalies need to be noted in some regions.

Temporal-spatial differences in lake water storage changes and their links to climate change throughout the Tibetan Plateau

Change in lake water storage is an important factor influencing hydrological cycle, regional environment, and climate on the Tibetan Plateau (TP) because of the large number (>1000 lakes) and huge areas (>46,500 km2) of lakes. Due to the lack of in situ lake level monitoring for most lakes, and long-term continuous satellite altimetry data for some large lakes, estimates of water storage changes for all lakes throughout the TP over a long time is challenging. We have estimated the lake water storage changes of 315 lakes (each lake is >10 km2) during the period of 1976–2013 through an empirical equation based on Shuttle Radar Topography Mission (SRTM) DEM (Digital Elevation Model) data and Landsat images. These lakes are located within endorheic basins and occupied approximately 80% of the total lake surface areas of the TP in 2013 based on the results of this study and Zhang et al. (2014). The results showed that the lake water storage decreased by 23.69 Gt from 1976 to 1990 and increased by 140.8 Gt from 1990 to 2013. Increased water storage was mainly concentrated in the central TP (regions A) and northern TP (region B). The increase in total lake surface area during the period 2000–2013 in region B (1981.6 km2) was greater than that in region A (1869.1 km2), but the increase in the water storage in the former was half of that in the latter, indicating that lake surface area changes cannot represent the degree of lake water storage change due to differences in the topography and lake size. Although the total variation in the rate of the lake water storage change (7.19 Gt/y) was similar to the rate of increase in the mass (7 ± 7 Gt/y) estimated from Gravity Recovery and Climate Experiment (GRACE) data for the whole region, the spatial distribution of these variations was largely different. During the period 2000–2013, a trend analysis revealed that precipitation was perhaps the primary reason for lake change throughout the TP, while a decreasing evaporation rate only contributed approximately 1.5%, 2.5% and 1.7% to the expansions of the lakes in regions A, C and D respectively. However, based on modern glacier mass balance observation data, we estimated that glacial meltwater may have contributed 22.2%, 39.8%, 50.6% and 100% to the increasing water storage during the period 2000–2013 by rough estimates in regions A, B, C and D, respectively, indicating that glacial meltwater perhaps was a primary contributor to lake expansion in region D, which was located in an extremely cold and dry climate with a broad distribution of glaciers.

Contribution of supra-permafrost discharge to thermokarst lake water balances on the northeastern Qinghai-Tibet Plateau

The seasonal hydrological mechanisms of two thermokarst lakes on the northeastern Qinghai-Tibet Plateau (QTP) were characterized by three-year intensive field observations and a water balance model. In three ice-free seasons, the supra-permafrost discharge contributed a mean ratio of over 170% of the precipitation. In the ice-cover seasons, the supra-permafrost discharge contribution varied between −20% and 22% of the water storage change. Results show that a large portion of the lake water storage change is because of the supra-permafrost discharge resulting from precipitation. Furthermore, a precipitation-subsurface runoff function is preliminarily identified in which the supra-permafrost discharge nonlinearly increased with more precipitation. Our results show that the recent lake expansion is linked with increasing supra-permafrost discharge dominated by precipitation. This study also suggests that we need to pay attention to the nonlinear increase of precipitation-controlled supra-permafrost discharge on the large lake expansion at the catchment scale in the QTP region, instead of only looking at the inputs (e.g., precipitation and river discharge) as shown in the previous studies.

Estimation of lakes water storage and their changes on the northwestern Tibetan Plateau based on bathymetric and Landsat data and driving force analyses

Lake water storage changes in four lakes were analyzed based on in situ bathymetric survey data and Landsat images in the extremely dry and cold northwestern Tibetan Plateau region. The results indicated that Bangdag Co and Aksai Chin Lake, which are glacier-fed and closed lakes, showed decreasing trends from 1976 to 1996, then increasing trend from 1996 to 2015, during which period water storage increased by 1.24 km3 and 1.37 km3, respectively, and 65% of the water storage increase in Aksai Chin Lake during this period occurring in 2006 and 2013. Longmu Co, which is a non-glacier-fed lake, exhibited little variation from 1976 to 1996 and a slight increase of 0.1 km3 from 1996 to 2015. The precipitation, temperature and potential evaporation (Ep) trends indicated that lake shrinkage from 1976 to 1996 was attributed to less precipitation and less meltwater at lower surface air temperatures. Decreased Ep (15.5 mm/y) contributed approximately 2% and 4% to the lake expansion of Aksai Chin Lake and Bangdag Co from 2000 to 2009. Based on the assumption of equal precipitation-evaporation for the study area, glacial meltwater contributed 76.6% to the lake expansion of Bangdag Co from 2000 to 2015. Because change in lakes' water storage showed a large difference between glacier-fed lakes and non-glacier-fed lakes from 1996 to 2015 under relatively high precipitation conditions, it is suggested that glacial meltwater exerted more influence on increasing lake water storage associated with rising temperatures.

Modeling and analysis of lake water storage changes on the Tibetan Plateau using multi-mission satellite data

Estimation of the water storage changes in the lakes of the Tibetan Plateau (TP) is essential for an accurate evaluation of climate change in this alpine region and its impact on the surrounding hydrologic environment. Because of the remoteness and poor accessibility of these alpine lakes, and a lack of lake bathymetric data, estimating their mass budget over the TP poses a considerable challenge. However, the integration of optical remote sensing images, satellite altimetry data, and gravimetry data makes it possible to monitor the overall variations in lake water storage in this extensive region. The ICESat/GLAS altimetry data used in this study reveal that most of the lakes in the TP showed a significant upward tendency (0.2–0.6m/year) in water level between 2003 and 2009, particularly those lakes that are supplied with a large proportion of glacial meltwater. A series of lake area data derived from Landsat MSS/TM/ETM+imagery over the past four decades indicate that during the 1970–1990 period most of the lakes experienced severe shrinkage, with only some of those in central and western Tibet undergoing expansion. During the 1990–2011 period, in contrast, the majority of the lakes on the TP displayed a remarkably expansion tendency. The total lake area increased from 35,638.11km2 in the early 1970s to 41,938.66km2 in 2011. Based on the statistical relationships between the extent of the lake surface area and lake water levels from 2003 to 2009, an empirical model for each of the region's 30 lakes is established to estimate the lake water level from the corresponding area data, thereby reconstructing time series of lake level data for each lake from the 1970s to 2011. Based on time series of lake area and water level data, a time series of lake water volume is also reconstructed. The results show that total lake water storage increased by 92.43km3 between the early 1970s and 2011, with lakes with an area larger than 100km2 accounting for 77.21% of the total lake water volume budget. Moreover, the GRACE signals confirm a similar spatial pattern in water mass changes, i.e., a significantly positive water mass balance in the north and center of the TP and mass loss in southeastern Tibet and along the Himalayas. The water mass budget (6.81km3/year) derived from satellite gravimetry signals in the Chiangtang Plateau are in good agreement with the estimated rising rate of 6.79km3/year of lake water storage in this region based on the empirical model developed in this study. The mechanism of lake water storage changes is discussed and analyzed with reference to previous studies.