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Lake-effect snowfall (LES) occurs when cold air moves across open lakes. LES is expected to occur more frequently over the TP, due to the intensified lake expansion caused by intensified global warming. Thus, there is an urgent need to comprehensively assess the LES over the TP. Here, we revealed that the LES is triggered by westerly southward shift leading to the drop in air temperature and is positively correlated with lake area, wind speed and longitude across 12 large lakes (>300 km2) based on satellite observations and reanalysis data. Using a sensitivity model simulation, we determined that large lakes in the southern TP contributed to more than 50% of the snowfall in the downwind area in 2013. Projections indicate that the westerly-triggered LES will increase under the future RCP4.5 climate warming scenario, highlighting the importance of developing adaptive policies to address the growing risks associated with future LES. [ABSTRACT FROM AUTHOR]

Over the past decades, changing climate has exerted pronounced influences on the cryo‐hydrological environment on the Tibetan Plateau. One major manifestation is the widespread lake expansions over Tibetan endorheic basins. The enlarged lake water surface areas are expected to significantly alter land‐atmosphere water fluxes, which in return may pose feedbacks to the climate system and hydrological processes. The goal of this study is to investigate the potential influences of the recent lake expansions on amplifying the evaporation flux over the basins of inner Tibetan Plateau (ITP). We detected that the ITP lakes have experienced a net inundation increase of 4,542.3 km2 during 2000–2015, about 95.6% of which was contributed by lakes larger than 1 km2. We further estimated the land and water evaporations based on multi‐source, available actual evapotranspiration (ETa) and potential evapotranspiration data sets, and in situ evaporation records. The differences between land ETa and lake water evaporation were employed to represent the evaporation alternation over newly inundated basin (named "land‐to‐lake" hereafter) areas. The land ETa was estimated based on the average of three commonly used gridded data sets while the over‐lake evaporation was calculated by the empirical correction of potential evaporation estimates by spatial interpolation of pan evaporation. A conservative estimate using the pan coefficient of 0.6 indicates that the newly inundated lake area may have led to a potential evaporation increase of 3.08 ± 1.08 Gt/year on the ITP. The increased evaporation flux is close to half of the recent annual growth rate of lake water storage in the ITP. Despite unneglectable uncertainties, our estimates initiate an important assessment of how the recent lake expansion across the ITP has influenced the local land‐atmosphere interactions and the water cycle. Accounting this evaporation amplification is crucial to reduce the uncertainty in estimating basin‐scale water budgets and projecting the regional water balance. [ABSTRACT FROM AUTHOR]

• High-turbidity events are triggered by wind waves with wind speeds of > 7 m s−1. • Sediment erosion and deposition are synchronous during HTEs. • Synchronism causes a near-lakebed turbid water layer and sustains the lutocline. High-turbidity events (HTEs) frequently occur in shallow lakes and can deeply influence lake ecosystems. However, the processes of sediment erosion and deposition are not fully understood. To investigate these processes, two investigative campaigns that integrate bed sediment measurements, sediment settling experiments, in-situ observations, or a hydrodynamics-sediment model were conducted to quantitatively study wind-induced HTEs in Lake Taihu, China. Cohesive sediments were massively entrained from the lakebed by wind waves when the wind speed exceeded its critical value of 7 m s−1, as estimated by water depth, triggering HTEs with turbidity waves of > 100 nephelometric turbidity units. The suspended sediment concentration was the net sediment flux of erosion (average: 5.9 mg m−2 s−1) and deposition (average: 5.5 mg m−2 s−1), which occurred synchronously for most of the HTEs and resulted in high temporal variation in suspended sediment concentration. This synchronism was determined by the critical erosional stress of lakebed sediments, which was spatially heterogeneous (0.017–0.055 N m−2) in a large lake. Equations for erosion and deposition processes were derived following the investigative campaigns and used to develop a cohesive sediment transport model for simulating HTEs in Lake Taihu. Simulations indicate that the synchronism of sediment erosion and deposition led to a near-lakebed turbid water layer during an HTE, which sustained the sediment lutocline in Lake Taihu. Further investigation should be conducted on the role of the near-lakebed turbid water layer during endogenous pollution in large eutrophic lakes. [ABSTRACT FROM AUTHOR]

The Landsat series of satellites provide a nearly continuous, high resolution data record of the Earth surface from the early 1970s through to the present. The public release of the entire Landsat archive, free of charge, along with modern computing capacity, has enabled Earth monitoring at the global scale with high spatial resolution. With the large data volume and seasonality varying across the globe, image selection is a particularly important challenge for regional and global multitemporal studies to remove the interference of seasonality from long term trends. This paper presents an automated method for selecting images for global scale lake mapping to minimize the influence of seasonality, while maintaining long term trends in lake surface area dynamics. Using historical meteorological data and a simple water balance model, we define the most stable period after the rainy season, when inflows equal outflows, independently for each Landsat tile and select images acquired during that ideal period for lake surface area mapping. The images selected using this method provide nearly complete global area coverage at decadal episodes for circa 2000 and circa 2014 from Landsat Enhanced Thematic Mapper Plus (ETM+) and Operational Land Imager (OLI) sensors, respectively. This method is being used in regional and global lake dynamics mapping projects, and is potentially applicable to any regional/global scale remote sensing application. [ABSTRACT FROM AUTHOR]

A substantial and rapid expansion beginning in the late 1990s of Siling Co, the largest endorheic lake on the central Tibetan Plateau (TP), has caused a measurable lithospheric deflection in the region adjacent to the lake. Current broad-scale measuring of this flexural response is mainly derived from InSAR processing techniques or time-consuming field campaigns. The rheological constraints of the lithosphere from the underlying lithospheric response to large lake loads in this region are not well understood. This paper highlights a more efficient spaceborne LiDAR remote sensing technique to measure the deflection in the vicinity of Siling Co and to investigate the mechanisms of the observed lithospheric response in order to garner a better understanding of the local rheology. A lake-adjacent deflection rate and Siling Co water load variations are calculated utilizing the Geoscience Laser Altimeter System (GLAS) onboard NASA’s Ice, Cloud and land Elevation Satellite (ICESat) and the joint NASA/USGS Landsat series of Earth observing satellites. A downward deflection rate of ∼5.6 mm/yr for the first 4 km of lake-adjacent land is calculated from the GLAS instrument, and this response is compared to the flexural outputs from a spherically symmetric, non-rotating, elastic, and isotropic (SNREI) Earth model in order to better understand the underlying mechanisms of the lithospheric response to the rapid increase of Siling Co loads. The modeled elastic response is ∼6.9 times lower than the GLAS derived flexure, thereby providing further evidence that a purely elastic lithospheric response cannot explain the deflection in this region. The relationship between the modeled elastic response and the GLAS derived flexure is applied to a long-term lake load change dataset to create the longest-running flexural response curve as caused by the last ∼40 years of Siling Co load variations, and these results show an accumulated lake-adjacent flexure of ∼12.6 cm from an overall lake load increase of 25.9 Gt. Our findings help to provide a better understanding of the lithospheric response to the recent expansion of Siling Co by introducing a new spaceborne laser altimeter derived technique to measure surface deformation caused by an extreme case of hydrologic loading. [ABSTRACT FROM AUTHOR]

Glacier mass loss in the Himalayas has far-reaching implications for the alteration of regional hydrologic regimes, an increased risk of glacial lake outburst, downstream water resource abundance, and contributions to sea level rise. However, the mass losses of Himalayan glaciers are not well understood towing to the scarcity of observations and the heterogeneous responses of Himalayan glaciers to climate change and local factors (e.g., glacier surge, interacting with proglacial lakes). In particular, there is a lack of understanding on the unique interactions between moraine-dammed glacial lakes and their effects on debris cover on valley glacier termini. In this study, we examined the temporal evolution of 151 large glacial lakes across the Himalayas and then classified these glacial lakes into three categories: proglacial lakes in contact with full or partial debris-covered glaciers (debris-contact lakes), ice cliff-contact lakes, and non-glacier-contact lakes. The results show that debris-contact lakes experienced a dramatic areal increase of 36.5% over the years 2000 to 2014, while the latter two categories of lakes remained generally stable. The majority of lake expansions occurred at the glacier front without marked lake level rises. This suggests that the rapid expansion of these debris-contact lakes can be largely attributed to the thinning of debris-covered ice as caused by the melting of glacial fronts and the subsequent glacial retreat. We reconstructed the height variations of glacier fronts in contact with 57 different proglacial lakes during the years 2000 to 2014. These reconstructed surface elevation changes of debris-covered, lake-contact glacier fronts reveal significant thinning trends with considerable lowering rates that range from 1.0 to 9.7 m/y. Our study reveals that a substantial average ice thinning of 3.9 m/y occurred at the glacier fronts that are in contact with glacial lakes. [ABSTRACT FROM AUTHOR]

The Himalaya, the world's highest mountain ranges, are home to a large group of glaciers and glacial lakes. Glacial lake outburst floods (GLOFs) in this region have resulted in catastrophic damages and fatalities in the past decades. The recent warming has caused dramatic glacial lake changes and increased potential GLOF risk in the Himalaya. However, our knowledge on the current state and change of glacial lakes in the entire Himalaya is limited. This study maps the current (2015) distribution of glacial lakes across the entire Himalaya and monitors the spatially-explicit evolution of glacial lakes over five time periods from 1990 to 2015 using a total of 348 Landsat images at 30 m resolution. The results show that 4950 glacial lakes in 2015 cover a total area of 455.3 ± 72.7 km 2 , mainly located between 4000 m and 5700 m above sea level. Himalayan glacial lakes expanded by approximately 14.1% from 1990 to 2015. The changing patterns of supraglacial lakes and proglacial lakes are rather complex, involving both lake disappearance and emergence. Many emergent glacial lakes are found at higher elevations, especially the new proglacial lakes, which have formed as a result of glacier retreat. Spatially heterogeneous changes of Himalayan glacial lakes are observed, with the most significant expansion occurring in the southern slopes of the central Himalaya. Increasing glacier meltwater induced by the Himalayan atmospheric warming is a primary cause for the observed lake expansion. This study provides primary data for future GLOF risk assessments. A total of 118 rapidly expanded glacial lakes are identified as potential vulnerable lakes for the priority of risk assessment. [ABSTRACT FROM AUTHOR]

Inland lakes, important water resources, play a crucial role in the global water cycle and are sensitive to climate change and human activities. There clearly is a pressing need to understand temporal and spatial variations of lakes at global and continental scales. The recent operation of Landsat 8 extends the unprecedented Landsat record to over 40 years, allowing long-term, large-scale lake dynamics mapping at high resolutions. Using our circa-2000 lake product derived from Landsat 7 images as a reference, this research produces a circa-2015 map of representative lake extents and distributions, and addresses seasonal and inter-annual lake area variability using Landsat 8 images acquired in lake stable seasons at a continental scale. Oceania is chosen here as a case study as it contains a large group of salt lakes that exhibit high area variability and has the most intensive image coverage during the first 2.5-year operation of Landsat 8. Accordingly, this paper describes an adaptive algorithm to automate lake mapping for various surface conditions using images acquired during lake stable seasons and a compositing scheme in the vector domain to generate a representative continental mosaic of lake extents from multi-temporal mapping. Our results demonstrate that these strategies and methods produce a highly reliable and representative composite of highly-variable lake extents across Oceania, and are potentially applicable to other large-scale lake mapping projects using multi-temporal data. [ABSTRACT FROM AUTHOR]

Glacial lakes, as an important component of the cryosphere in the southeastern Tibetan Plateau (SETP) in response to climate change, pose significant threats to the downstream lives and properties of people, engineering construction, and ecological environment via outburst floods, yet we currently have limited knowledge of their distribution, evolution, and the driving mechanism of rapid expansions due to the low accessibility and harsh natural conditions. By integrating optical imagery, satellite altimetry and digital elevation model (DEM), this study presents a regional-scale investigation of glacial lake dynamics across two river basins of the SETP during 1988–2013 and further explores the glacial-hydrogeomorphic process of rapidly expanding lakes. In total 1278 and 1396 glacial lakes were inventoried in 1988 and 2013, respectively. Approximately 92.4% of the lakes in 2013 are not in contact with modern glaciers, and the remaining 7.6% includes 27 (1.9%) debris-contact lakes (in contact with debris-covered ice) and 80 (5.7%) cirque lakes. In categorizing lake variations, we found that debris-contact proglacial lakes experienced much more rapid expansions (∼75%) than cirque lakes (∼7%) and non-glacier-contact lakes (∼3%). To explore the cause of rapid expansion for these debris-contact lakes, we further investigated the mass balance of parent glaciers and elevation changes in lake surfaces and debris-covered glacier tongues using time-series Landsat images, ICESat altimetry, and DEM. Results reveal that the upstream expansion of debris-contact proglacial lakes was not directly associated with rising water levels but with a geomorphological alternation of upstream lake basins caused by melting-induced debris subsidence at glacier termini. This suggests that the hydrogeomorphic process of glacier thinning and retreat, in comparison with direct glacial meltwater alone, may have played a dominant role in the recent glacial lake expansion observed across the SETP. Our findings assist in understanding the expansion mechanism of debris-contact proglacial lakes, which facilitates early recognition of potential glacial lake hazards in this region. [ABSTRACT FROM AUTHOR]

The Sara Us River is located along the boundary of the Mu Us Desert and the Chinese Loess Plateau in northern China. The river has cut down through Quaternary sediments creating 70–80 m deep valleys with thick lacustrine/aeolian sequences exposed. We applied optical stimulated luminescence on sediments from a Holocene section of aeolian sand/lacustrine deposits in the top of the river valley. The dating results show that a humid period existed from 7.1 to 2.0 ka ago as evidenced by two layers of peat and lacustrine sediments. However, compared to other published Holocene sections in the Sara Us River valleys close to the section under studying, the local environment experienced very complicated changes during the Holocene. All of the sections recorded a period with drought and/or cold before the Holocene at around 13 ka, and an episode of aridity after about 2 ka ago as evidenced by the layers of aeolian sand. However, the ages of the lacustrine and peat layers in these sections are substantially different. Geomorphological analysis by digital elevation models does not support the existence of a mega lake covering the study area at 2 ka. The intricate environmental changes may have been caused by the meandering of the Sara Us River. Environmental changes also strongly affected human migration in this area, which is documented by Chinese historical records. [ABSTRACT FROM AUTHOR]

High-altitude lakes in the Tibetan Plateau (TP) showed strong spatio-temporal variability during past decades. The lake dynamics could be associated with several important factors including lake type, supply of glacial meltwater, local climate variations. It is important to differentiate these factors when analyzing the driving forces of lakes dynamics. With a focus on lakes over the Tanggula Mountains of the central TP, this study investigates the temporal evolution patterns of lake area and water level of different types: glacier-fed closed lake, non-glacier-fed closed lake and upstream lake (draining into closed lakes). We collected all available Landsat archive data and quantified the inter-annual variability of lake extents. Results reveal accelerated expansions of both glacier-fed and non-glacier-fed lakes during 1970s-2013, and different temporal patterns of the two types of lakes: the non-glacier-fed lakes displayed a batch-wise growth pattern, with obvious growth in 2002, 2005 and 2011 and slight changes in other years, while glacier-fed lakes showed steady expanding tendency. The contrasting patterns are confirmed by distinct lake level changes between the two groups derived from satellite altimetry during 2003-2013. The upstream lakes remained basically stable due to natural drainage regulation. The intermittent expansions for non-glacier-fed lakes are found to be related to excessive precipitation events and positive 'precipitation-evaporation'. In contrast, glacier-fed lake changes showed weak correlations with precipitation variations, which implies a joint contribution from glacial meltwater to water budgets. Our study suggests that glacial meltwater supply may have an equivalent influence on lake growth with precipitation/evaporation in the study area. [ABSTRACT FROM AUTHOR]

Two major oases in the lower reaches of Heihe River, Inner Mongolia of China, the desertified ancient Juyanze oasis (AJO) and the modern Ejina oasis (MEO), experienced dramatic environmental changes and human migrations as documented in historic records. The processes and mechanisms of their evolution are the key for us to understand the environmental changes and human activities in this region, yet are still unclear. This study provides an evolution chronology of these two oases by analyzing the optical dating records from MEO and 14C dating records from AJO and discusses their evolution mechanisms based on drainage network analysis and field investigations. The optical dating samples collected from aeolian sands below humus layers in Populus euphratica woodlands on MEO indicate that this oasis developed between 1.05 and 0.45 ka ago, while the 14C dating samples collected from a number of dead P. euphratica trees from AJO consistently suggest that the complete desertification of AJO occurred before ~400 cal. a BP. These new dating results imply that the two oases evolved simultaneously but in opposite directions. That is, AJO desertified while MEO developed gradually in the last 1 ka. Climate change occurring over the last 1 ka in northern China cannot explain the opposite evolution directions of these two adjacent oases. The drainage network analysis based on digital elevation models (DEMs) and field observations and the dates (~0.5 ka) of the top lacustrine layer from GaxuNur Lake north of MEO suggest that the evolution of the two oases was mainly governed by Heihe River migration. [ABSTRACT FROM PUBLISHER]

Regional- to global-scale lake maps can now be produced using existing technology and freely available data and serve as powerful tools for a variety of lake- and water-related studies. The accuracy of these studies depends in part on the accuracy of the lake map that they use. Mapping lakes using remote sensing requires a careful study of error and uncertainty. Errors in lake maps are caused by sensor-specific, lake-specific, and processing-specific factors. These can be further broken down to spatial, spectral/radiometric, and temporal factors. In this study, we analyse and compare these factors using modern and historical Landsat images along with intensive ground surveys of lakes in northern Alaska. Percentage error in lake area (relative to lake size) decreases for larger and more circular lakes, making a minimum size threshold an effective error mitigation practice. Image resampling involved in image transformation significantly increased error in lake area and is easily avoided by performing co-registration in the vector domain. Spectral properties varied for individual lakes due to depth, suspended sediment, vegetation, and otherin situfactors, necessitating a normalized water index and independently derived threshold values for each lake. For lake change detection studies, spatially degrading a finer resolution image to the resolution of the coarser image (a common practice) does not significantly affect the difference in observed lake area. Due to the large numbers of lakes, particularly in the climatologically sensitive Arctic region, small errors in individual lake areas can compound to significantly impact results on regional to global scales. This study is intended to inform future static and multitemporal lake remote-sensing studies by evaluating errors and uncertainties in lake area, as measured by remote sensing. [ABSTRACT FROM AUTHOR]

Glacial lakes in alpine regions are sensitive to climate change. Mapping and monitoring these lakes would improve our understanding of regional climate change and glacier-related hazards. However, glacial lake mapping over large areas using remote sensing remains a challenge because of various disturbing factors in glacial and periglacial environments. This article presents an automated mapping algorithm based on hierarchical image segmentation and terrain analysis to delineate glacial lake extents. In this algorithm, each glacial lake is delineated with a local segmentation value, and the topographic features derived from digital elevation models (DEMs) are also used to separate mountain shadows from glacial lakes. About 100 scenes of Landsat Thematic Mapper/Enhanced Thematic Mapper Plus (TM/ETM+) images from circa 1990, circa 2000 and 2009 were used to map the glacial lakes and their changes over the entire Himalayas. The results show that the algorithm can map the glacial lakes effectively and efficiently. Mountain shadows or melting glaciers can be differentiated from glacial lakes automatically, and those lakes with mountain shadows can also be identified. Area changes of more than 1000 glacial lakes show that the glacial lakes in the Himalayas have experienced mixed directions of change, while the overall lake areas are expanding at an accelerated rate in the past two decades, indicating great changes to the glacial lakes in the Himalayas. [ABSTRACT FROM AUTHOR]

Abstract: The landscape on the Arctic Coastal Plain (ACP) of Alaska is dominated by thousands of thaw (thermokarst) lakes and associated drained thaw lake basins (DTLBs). Knowledge of the DTLBs benefits our understanding of thaw lake dynamics, carbon cycles, and paleo-climatic change on the ACP since the end of the Late Glacial. This study initializes the application of high-resolution digital elevation models (DEMs) into a systematic reconstruction of DTLBs on the western ACP and adjacent northern Arctic Foothills. The method combines a machine-based detection algorithm automating the delineation of basin paleoshorelines on IfSAR DEM data and a posterior quality control with the aid of high-resolution aerial photograph and Landsat-5 TM imagery. A total of ~3590km2 of thaw lakes and ~10130km2 of DTLBs were mapped, with an overall accuracy of 99.2% and a Kappa coefficient of 0.988. The delineated DTLB extents are conservative, as validated from eleven field-sampled paleoshorelines. A variety of topologic patterns such as merging, nesting, and overtopping are presented in the reconstructed DTLBs. Basin paleoshoreline levels are subject to average uncertainties of 0.4–0.7 m. The combined area of thaw lakes and DTLBs accounts for 57.1% of the western ACP and 23.2% of the northern Arctic Foothills in the study site. Regional analysis of several spatial and topographic characteristics demonstrates a distinct heterogeneity among the younger Outer Coastal Plain (YOCP), Outer Coastal Plain (OCP), Inner Coastal Plain (ICP), and the Arctic Foothills. Generally, the areal density of DTLBs decreases progressively on higher and older surfaces. The ICP has a lake–DTLB area ratio (0.37) greater than that in the other regions. DTLB bathymetry presents a positive correlation with surface elevation: basin maximum depths range from ~2.0m on the YOCP to ~ 8.0m on the Arctic Foothills. Given the reconstructed DTLBs, a total of 31.9 (±4.9) gigatons of net water drainage were estimated for the entire study area. [Copyright &y& Elsevier]

Of the approximately 6700 lakes and reservoirs larger than 1 km2 in the Contiguous United States (CONUS), only ~430 (~6%) are actively gaged by the United States Geological Survey (USGS) or their partners and are available for download through the National Water Information System database. Remote sensing analysis provides a means to fill in these data gaps in order to glean a better understanding of the spatiotemporal water level changes across the CONUS. This study takes advantage of two-plus years of NASA's ICESat-2 (IS-2) ATLAS photon data (ATL03 products) in order to derive water level changes for ~6200 overlapping lakes and reservoirs (>1 km2) in the CONUS. Interactive visualizations of large spatial datasets are becoming more commonplace as data volumes for new Earth observing sensors have markedly increased in recent years. We present such a visualization created from an automated cluster computing workflow that utilizes tens of billions of ATLAS photons which derives water level changes for all of the overlapping lakes and reservoirs in the CONUS. Furthermore, users of this interactive website can download segmented and clustered IS-2 ATL03 photons for each individual waterbody so that they may run their own analysis. We examine ~19,000 IS-2 derived water level changes that are spatially and temporally coincident with water level changes from USGS gages and find high agreement with our results as compared to the in situ gage data. The mean squared error (MSE) and the mean absolute error (MAE) between these two products are 1 cm and 6 cm, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The November 1996 jökulhlaup that burst from the Vatnajökull ice cap onto Skeiðarársandur was the highest-magnitude flood ever measured on the largest active glacial outwash plain (sandur). Centimeter-scale elevation transects, measured from repeat-pass airborne laser altimetry missions flown in 1996 (pre-flood), 1997, and 2001, show that sediment deposition exceeded erosion across the central Skeiðarársandur and established an average net elevation gain of +22 cm for the event. Net elevation gains of +29 and +24 cm occurred in braided channels of the Gígjukvísl and Skeiðará rivers, respectively. Nearly half of these gains, however, were removed within 4 years, and the two rivers contrast strongly in style of erosional/depositional impact and subsequent recovery. In the Gígjukvísl, the 1996 jökulhlaup caused massive sediment deposition (up to ∼12 m) near the ice margin and intense “mega-forming” of braided channels and bars downstream. Post-jökulhlaup recovery (1997–2001) was characterized by rapid erosion (−0.5 m) of ice-proximal sediments and their transport to downstream reaches, and eradication of the mega-forms. In contrast, the Skeiðará displays minimal post-jökulhlaup sediment erosion in its upstream reaches and little change in braided channel relief. This contrast between river systems is attributed to the presence of a previously studied ∼2-km wide ice-marginal trench, caused by glacier retreat and lowering, which contained flows of the Gígjukvísl but not the Skeiðará prior to dispersal onto the outwash plain. Rapid removal of jökulhlaup deposits from this trench suggests that in terms of long-term evolution of the sandur, such features only delay downstream migration of jökulhlaup-derived sediment. These results, therefore, suggest that the net geomorphic impact of jökulhlaups on surface relief of Skeiðarársandur, while profound in the short term, may be eradicated within years to decades. [Copyright &y& Elsevier]

The single-ray backprojection problem refers to the process of determining ground coordinates of pixels in a single aerial image with the support of a digital surface model or a digital elevation model. Several methods have been employed to solve this problem. The iterative photogrammetric (IP) method, based on the inverse collinearity equations, is widely used in photogrammetry. The ray-tracing (RT) method, which is popular in computer graphics, computes the coordinates by intersecting the view ray with the surface. A third one is an iterative ray-tracing (IRT) method, which finds the intersection point by extending the view ray towards the surface by a certain step once a time until it hits the surface. Since the methods become diversified, there is a need to compare and evaluate them. This paper analyzes the principles of these three methods, tests them using a variety of data sets, and provides a comprehensive comparison on their strategies, parameter selection, divergence, occlusion-compliance, precision, robustness, and efficiency. The major difference of these methods is in the strategy of computing the intersection between the view ray and the surface, and this leads to their varied performance. It is found that the IP method is the most computationally efficient and can produce precise coordinates for simple surfaces, but it may surfer from the divergence and occlusion-induced problems for complicated ones. The rigorous RT method is precise, occlusion-compliant and parameter-free, but it is computationally intensive. The IRT method is intermediate in terms of efficiency. If the initial step is small enough, it can adequately address the occlusion-induced problem and produce satisfactory coordinates for complicated surfaces. This comparison provides a guide to method selection for the single-ray backprojection problem. [Copyright &y& Elsevier]

Oceanographic data are complex in that they incorporate multiple measurements and various scales. They are truly three-dimensional, and often vary in time. As the ability to acquire data is constantly being enhanced by the introduction of new and increasingly sophisticated instruments, it is challenging for oceanographers to inspect oceanographic processes by analyzing the complex data conventionally. In this article, we discuss an integrated GIS/visualization approach to visualize oceanographic data in Monterey Bay in order to get a better understanding of upwelling processes. The GIS system performs data interpolation, unifies map projection, and filters the processed data to a computer visualization package. The multidimensional visualization and animation features of the visualization tool are used to gain insight into marine upwelling processes. In such an integrated environment, the water properties (i.e., temperature, salinity, and density) in Monterey Bay during upwelling are visualized, and the characteristics of upwelling are examined. The center of upwelling and the maximum depth of upwelling in Monterey Bay during the 1995 upwelling season are identified. The differences in temperature changing patterns between a typical upwelling year and an El Nino year are shown in this study. The integration of GIS and visualization makes it easier for oceanographers to discover and understand upwelling. [ABSTRACT FROM AUTHOR]

Addressing seasonal water uncertainties and increased power generation demand has sparked a global rise in large-scale hydropower projects. To this end, the Blue Nile impoundment behind the Grand Ethiopian Renaissance Dam (GERD) will encompass an areal extent of ~1763.3 km2 and hold ~67.37 Gt (km3) of water with maximum seasonal load changes of ~27.93 (41% of total)—~36.46 Gt (54% of total) during projected operational scenarios. Five different digital surface models (DSMs) are compared to spatially overlapping spaceborne altimeter products and hydrologic loads for the GERD are derived from the DSM with the least absolute elevation difference. The elastic responses to several filling and operational strategies for the GERD are modeled using a spherically symmetric, non-rotating, elastic, and isotropic (SNREI) Earth model. The maximum vertical and horizontal flexural responses from the full GERD impoundment are estimated to be 11.99 and 1.99 cm, regardless of the full impoundment period length. The vertical and horizontal displacements from the highest amplitude seasonal reservoir operational scenarios are 38–55% and 34–48% of the full deformation, respectively. The timing and rate of reservoir inflow and outflow affects the hydrologic load density on the Earth's surface, and, as such, affects not only the total elastic response but also the distance that the deformation extends from the reservoir's body. The magnitudes of the hydrologic-induced deformation are directly related to the size and timing of reservoir fluxes, and an increased knowledge of the extent and magnitude of this deformation provides meaningful information to stakeholders to better understand the effects from many different impoundment and operational strategies. [ABSTRACT FROM AUTHOR]

The Pleistocene sand sea on the Arctic Coastal Plain (ACP) of northern Alaska is underlain by an ancient sand dune field, a geological feature that affects regional lake characteristics. Many of these lakes, which cover approximately 20 % of the Pleistocene sand sea, are relatively deep (up to 25 m). In addition to the natural importance of ACP sand sea lakes for water storage, energy balance, and ecological habitat, the need for winter water for industrial development and exploration activities makes lakes in this region a valuable resource. However, ACP sand sea lakes have received little prior study. Here, we collect in situ bathymetric data to test 12 model variants for predicting sand sea lake depth based on analysis of Landsat-8 Operational Land Imager (OLI) images. Lake depth gradients were measured at 17 lakes in midsummer 2017 using a Humminbird 798ci HD SI Combo automatic sonar system. The field-measured data points were compared to red–green–blue (RGB) bands of a Landsat-8 OLI image acquired on 8 August 2016 to select and calibrate the most accurate spectral-depth model for each study lake and map bathymetry. Exponential functions using a simple band ratio (with bands selected based on lake turbidity and bed substrate) yielded the most successful model variants. For each lake, the most accurate model explained 81.8 % of the variation in depth, on average. Modeled lake bathymetries were integrated with remotely sensed lake surface area to quantify lake water storage volumes, which ranged from 1.056×10-3 to 57.416×10-3 km 3. Due to variations in depth maxima, substrate, and turbidity between lakes, a regional model is currently infeasible, rendering necessary the acquisition of additional in situ data with which to develop a regional model solution. Estimating lake water volumes using remote sensing will facilitate better management of expanding development activities and serve as a baseline by which to evaluate future responses to ongoing and rapid climate change in the Arctic. All sonar depth data and modeled lake bathymetry rasters can be freely accessed at 10.18739/A2SN01440 (Simpson and Arp, 2018) and 10.18739/A2HT2GC6G (Simpson, 2019), respectively. [ABSTRACT FROM AUTHOR]

Over a hundred sizable lakes, some even larger than ~1 km2, are distributed across the lowlands between megadunes in the southeastern Badain Jaran Desert (BJD), northwest China. With rather limited precipitation and hardly any surface runoff, these lakes are fed mainly by groundwater. However, the source of the groundwater and the groundwater discharge rates to these lakes are poorly understood. Water level and temperature of four representative lakes in the southeastern BJD were monitored continuously between 2013 and 2017. Water surface evaporation and rainfall in this area were also measured. Combining these acquired data, groundwater discharge rates were estimated using water balance models. The results show that the four lakes have similar recharge and discharge patterns, but at different average net groundwater discharge rates ranging from 1.79 to 3.09 mm d−1. The lake level variation mainly depends on groundwater discharge and lake surface evaporation. We found that diurnal lake level variation may be controlled by earth tide and atmospheric pressure change, and is five times greater than the evaporation. The desert precipitation and deep confined groundwater with high temperature were found also recharging the desert lakes. An Empirical Mode Decomposition (EMD) method was used to identify the lake level trend. All lake levels increased over the last four years, except one decreased in 2015 and 2016. The lake levels' increasing trend is synchronously similar with the precipitation in north China. This study analyzes annual and seasonal lake level variations, and also finds the diurnal water cycle between the groundwater and lake water for the first time. [ABSTRACT FROM AUTHOR]

The Pleistocene Sand Sea on the Arctic Coastal Plain (ACP) of northern Alaska is underlain by an ancient sand dune field, a geological feature that affects regional lake characteristics. Many of these lakes, which cover approximately 20% of the Pleistocene Sand Sea, are relatively deep (up to 25m). In addition to the natural importance of ACP Sand Sea lakes for water storage, energy balance, and ecological habitat, the need for winter water for industrial development and exploration activities makes lakes in this region a valuable resource. However, ACP Sand Sea lakes have received little prior study. Here, we use in situ bathymetric data to test 12 model variants for predicting Sand Sea lake depth based on analysis of Landast-8 Operational Land Imager (OLI) images. Lake depth gradients were measured at 17 lakes in mid-summer 2017 using a HumminBird 798ci HD SI Combo automatic sonar system (Simpson and Arp, 2018). The field measured data points were compared to Red-Green-Blue (RGB) bands of a Landsat-8 OLI image acquired on 8 August 2016 to select and calibrate the most accurate spectral-depth model for each study lake and estimate bathymetry (Simpson, 2019). Exponential functions using a simple band ratio (with bands selected based on lake turbidity and bed substrate) yielded the most successful model variants. For each lake, the most accurate model explained 81.8% of the variation in depth, on average. Modeled lake bathymetries were integrated with remotely sensed lake surface area to quantify lake water storage volumes, which ranged from 1.056 x 10-3xkm³ to 57.416 x 10-3 km³. Due to variation in depth maxima, substrate, and turbidity between lakes, a regional model is currently infeasible, rendering necessary the acquisition of additional in situ data with which to develop a regional model solution. Estimating lake water volumes using remote sensing will facilitate better management of expanding development activities and serve as a baseline by which to evaluate future responses to ongoing and rapid climate change in the Arctic. [ABSTRACT FROM AUTHOR]

Lakes and reservoirs are ubiquitous across global landscapes, functioning as the largest repository of liquid surface freshwater, hotspots of carbon cycling, and sentinels of climate change. Although typically considered lentic (hydrologically stationary) environments, lakes are an integral part of global drainage networks. Through perennial and intermittent hydrological connections, lakes often interact with each other, and these connections actively affect water mass, quality, and energy balances in both lacustrine and fluvial systems. Deciphering how global lakes are hydrologically interconnected (or the so-called "lake drainage topology") is not only important for lake change attribution but also increasingly critical for discharge, sediment, and carbon modeling. Despite the proliferation of river hydrography data, lakes remain poorly represented in routing models, partially because there has been no global-scale hydrography dataset tailored to lake drainage basins and networks. Here, we introduce the global Lake drainage Topology and Catchment database (Lake-TopoCat), which reveals detailed lake hydrography information with careful consideration of possible multifurcation. Lake-TopoCat contains the outlet(s) and catchment(s) of each lake; the interconnecting reaches among lakes; and a wide suite of attributes depicting lake drainage topology such as upstream and downstream relationship, drainage distance between lakes, and a priori drainage type and connectivity with river networks. Using the HydroLAKES v1.0 (Messager et al., 2016) global lake mask, Lake-TopoCat identifies ∼ 1.46 million outlets for ∼ 1.43 million lakes larger than 10 ha and delineates 77.5×106 km2 of lake catchments covering 57 % of the Earth's landmass except Antarctica. The global lakes are interconnected by ∼ 3 million reaches, derived from MERIT Hydro v1.0.1 (Yamazaki et al., 2019), stretching a total distance of ∼10×106 km , of which ∼ 80 % are shorter than 10 km. With such unprecedented lake hydrography details, Lake-TopoCat contributes towards a globally coupled lake–river routing model. It may also facilitate a variety of limnological applications such as attributing water quality from lake scale to basin scale, tracing inter-lake fish migration due to changing climate, monitoring fluvial–lacustrine connectivity, and improving estimates of terrestrial carbon fluxes. Lake-TopoCat is freely accessible at 10.5281/zenodo.7916729 (Sikder et al., 2023). [ABSTRACT FROM AUTHOR]

• Unprecedented lake expansion occurred in 2017–2018 on the inner Tibetan Plateau. • The rapid lake expansion exerted a significant impact on regional ecosystems and human living environments. • The rapid lake expansion was mainly attributed to anomalously high precipitation. Extreme events on the Tibetan Plateau (TP) have become increasingly frequent and severe in recent decades in tandem with rapid climate warming and moistening. Thus, it is highly important to investigate their processes, causes and environmental impacts. Using in-situ observations of lake level changes in combination with satellite altimetry data, we showed that lakes on the central TP (CTP) expanded unprecedentedly in 2017–2018, with lake level increases of 1.4–2.8 m at the five observed lakes. This extreme lake expansion occurred over almost the entire inner TP, which was mainly attributed to anomalously high precipitation (approximately 43–97% higher in 2017–2018 than in normal years on the CTP). The rapid lake expansion posed a substantial threat to regional ecosystems, infrastructure, and even residential habitats. Therefore, it is necessary to identify the potential sites threatened by lake expansion on the TP using high-resolution satellite images and perform near real-time observations of lake level changes through satellite and in-situ observations. [ABSTRACT FROM AUTHOR]

Uncertainty regarding the timing of the highest Holocene water level of enclosed Dali Lake in northern China has led to controversy about whether the East Asian summer monsoon (EASM) peaked in the early Holocene or the mid-Holocene. Therefore, a record combining a reliable chronology with unambiguous lake level indicators is essential to resolve the issue. In this study, we established a temporal sequence of well-preserved paleolake shorelines at different elevations around Dali Lake using quartz optically stimulated luminescence (OSL) dating. Combining the new OSL-based chronological data with the previously published ages of beach ridges, we constructed an integrated lake level record for Dali Lake since the last deglaciation; the record is chronologically well-constrained and provides a clearer representation of lake level changes than previous studies. The main findings are as follows: (1) the level of Dali Lake rose gradually during 14.5–8.0 ka and reached a highest level during 8.0–6.0 ka that was ~61 m higher than today, before gradually declining after ~6.0 ka; (2) although the short-lived highstand of Dali Lake during the early Holocene was caused by both monsoon precipitation and snow/ice meltwater influx, the mid-Holocene lake level maximum was mainly the result of increased monsoon precipitation. These findings indicate that the EASM maximum in the region occurred during the mid-Holocene, which is supported by precipitation-proxy records from the EASM margin; (3) a major decline (~30 m) of the level of Dali Lake occurred at ~4.2 ka, reflecting a regional-scale drought event in northern China. Combined with near-contemporaneous frequent floods in the lower Yellow River, we propose that the pattern of "drought in northern China, flooding in central China" occurred during ~4.2–3.8 ka, triggering the migration of the prehistoric human population of the area to the central Plain of China. This population migration may have destabilized the existing social order and promoted the emergence of more complex societies, leading to the development of early civilization in north-central China. [ABSTRACT FROM AUTHOR]

Lakes and reservoirs are ubiquitous across global landscapes, functioning as the largest repository of liquid surface freshwater, hotspots of carbon cycling, and 'sentinels" of climate change. Although typically considered as lentic 15 (hydrologically stationary) environments, lakes are an integral part of global drainage networks. Through perennial and intermittent hydrological connections, lakes often communicate with each other, and these connections actively affect water mass, quality, and energy balances in both lacustrine and fluvial systems. Deciphering how global lakes are hydrologically interconnected, or the so-called "lake drainage topology", is not only important to lake change attribution, but also increasingly critical to discharge, sediment, and carbon modeling. Despite the proliferation of river hydrography data, lakes remain poorly 20 represented in routing models, partially because there has been no global-scale hydrography dataset tailored to lake drainage basins and networks. Here, we introduce the global Lake drainage Topology and Catchment database, or "Lake-TopoCat", which reveals detailed lake hydrography information with a careful consideration of possible multifurcation. Lake-TopoCat contains the outlet(s) and catchment(s) of each lake, the inter-connecting reaches among lakes, and a wide suite of attributes depicting lake drainage topology such as upstream and downstream relationship, drainage distance between lakes, and a priori 25 drainage type and connectivity with river networks. Using the HydroLAKES (v1.0) global lake mask, the Lake-TopoCat v1.0 identifies -1.46 million outlets for -1.43 million lakes larger than 10 ha and delineates 77.5 million km2 of lake catchments covering 57% of the Earth's landmass except Antarctica. The global lakes are interconnected by -3 million reaches, derived from MERIT Hydro (v1.0.1), stretching a total distance of -10 million km, -80% of which are shorter than 10 km. With such unprecedented lake hydrography details, Lake-TopoCat may facilitate a variety of limnological applications including water 30 quality diagnosis, agriculture and fisheries, lacustrine connectivity monitoring, and integrated lake-river modeling. It is freely accessible at https://doi.org/10.5281/zenodo.7420810 (Sikder et al., 2022). [ABSTRACT FROM AUTHOR]

With rapid population growth and socioeconomic development over the last century, a great number of dams/reservoirs have been constructed globally to meet various needs. China has strong economical and societal demands for constructing dams and reservoirs. The official statistics reported more than 98 000 dams/reservoirs in China, including nearly 40 % of the world's largest dams. Despite the availability of several global-scale dam/reservoir databases (e.g., the Global Reservoir and Dam database (GRanD), the GlObal geOreferenced Database of Dams (GOODD), and the Georeferenced global Dams And Reservoirs (GeoDAR)), these databases have insufficient coverage of the reservoirs in China, especially for small or newly constructed ones. The lack of reservoir information impedes the estimation of water budgets and the evaluation of dam impacts on hydrologic and nutrient fluxes for China and its downstream countries. Therefore, we presented the China Reservoir Dataset (CRD), which contains 97 435 reservoir polygons and fundamental attribute information (e.g., name and storage capacity) based on existing dam/reservoir products, national basic geographic datasets, multi-source open map data, and multi-level governmental yearbooks and databases. The reservoirs compiled in the CRD have a total maximum water inundation area of 50 085.21 km 2 and a total storage capacity of about 979.62 km 3 (924.96–1060.59 km 3). The quantity of reservoirs decreases from the southeast to the northwest, and the density hotspots mainly occur in hilly regions and large plains, with the Yangtze River basin dominating in reservoir count, area, and storage capacity. We found that these spatial accumulations of reservoirs are closely related to China's socioeconomic development and the implementation of major policies. Finally, we presented the comparison of the CRD with GOODD, GeoDAR, and GRanD databases. The CRD has significantly increased the reservoir count, area, and storage capacity in China, especially for reservoirs smaller than 1 km 2. The CRD database provides more comprehensive reservoir spatial and attribute information and is expected to benefit water resources managements and the understanding of ecological and environmental impacts of dams across China and its affected transboundary basins. The CRD database is publicly available at 10.5281/zenodo.6984619 (Song et al., 2022). [ABSTRACT FROM AUTHOR]

When conducting image registration in the U.S. state of Alaska, it is very difficult to locate satisfactory ground control points because ice, snow, and lakes cover much of the ground. However, GCPs can be located by seeking stable points from the extracted lake data. This paper defines a process to estimate the deepest points of lakes as the most stable ground control points for registration. We estimate the deepest point of a lake by computing the center point of the largest inner circle (LIC) of the polygon representing the lake. An LIC-seeking method based on Voronoi diagrams is proposed, and an algorithm based on medial axis simplification (MAS) is introduced. The proposed design also incorporates parallel data computing. A key issue of selecting a policy for partitioning vector data is carefully studied, the selected policy that equalize the algorithm complexity is proved the most optimized policy for vector parallel processing. Using several experimental applications, we conclude that the presented approach accurately estimates the deepest points in Alaskan lakes; furthermore, we gain perfect efficiency using MAS and a policy of algorithm complexity equalization. [ABSTRACT FROM AUTHOR]

Rapid lake expansions along with intensive glacier loss in the Tibetan Plateau (TP) in recent decades indicate an enhanced hydrological circulation. Well-preserved paleo-shorelines up to ∼200 m above modern levels in the TP attest to much greater lake expansions in the past and serve as analogues for future lake evolution under climate changes. Mega-lakes in the inner TP, defined by the highest paleo-shorelines, were mainly formed in the early–middle Holocene and are mainly attributed to a high monsoonal rainfall. However, the effect of melting glaciers on the mega-lakes was rarely evaluated, and reliable mega-lake ages are scarce, especially in the northwestern TP (NWTP). We studied six mega-lakes in the NWTP by dating the highest paleo-shorelines using optical dating of multiple and single grains and then reconstructing the paleo-hydrology. The results show that four mega-lakes existed during the last deglacial (16.3–12.6 ka). They had lake levels 53–269 m higher than today and areas up to 7.3 times larger than the modern lakes, containing up to 105.4 km3 more water. A comparison of mega-lakes across the TP and correlation with independent paleoclimatic records reveal that these mega-lakes attained larger relative sizes (lake area/basin land area ratio) under a dry climate and intensive glacier melting during the last deglacial than the non-glacier-fed mega-lakes that developed in response to the early–middle Holocene rainfall maximum. We suggest that they were formed by melting glaciers, and therefore glaciers had major impacts on long-term lake evolution in the NWTP. • Post-IR IRSL dating of K-feldspar single-grains determined paleo-shoreline ages. • Four mega-lakes developed in the northwestern Tibetan Plateau in the last deglacial. • The last deglacial mega-lakes were formed by melting glaciers. [ABSTRACT FROM AUTHOR]

Dams and reservoirs are among the most widespread human-made infrastructures on Earth. Despite their societal and environmental significance, spatial inventories of dams and reservoirs, even for the large ones, are insufficient. A dilemma of the existing georeferenced dam datasets is the polarized focus on either dam quantity and spatial coverage (e.g., GlObal geOreferenced Database of Dams, GOODD) or detailed attributes for a limited dam quantity or region (e.g., GRanD (Global Reservoir and Dam database) and national inventories). One of the most comprehensive datasets, the World Register of Dams (WRD), maintained by the International Commission on Large Dams (ICOLD), documents nearly 60 000 dams with an extensive suite of attributes. Unfortunately, the WRD records provide no geographic coordinates, limiting the benefits of their attributes for spatially explicit applications. To bridge the gap between attribute accessibility and spatial explicitness, we introduce the Georeferenced global Dams And Reservoirs (GeoDAR) dataset, created by utilizing the Google Maps geocoding application programming interface (API) and multi-source inventories. We release GeoDAR in two successive versions (v1.0 and v1.1) at 10.5281/zenodo.6163413 (Wang et al., 2022). GeoDAR v1.0 holds 22 560 dam points georeferenced from the WRD, whereas v1.1 consists of (a) 24 783 dam points after a harmonization between GeoDAR v1.0 and GRanD v1.3 and (b) 21 515 reservoir polygons retrieved from high-resolution water masks based on a one-to-one relationship between dams and reservoirs. Due to geocoding challenges, GeoDAR spatially resolved ∼ 40 % of the records in the WRD, which, however, comprise over 90 % of the total reservoir area, catchment area, and reservoir storage capacity. GeoDAR does not release the proprietary WRD attributes, but upon individual user requests we may provide assistance in associating GeoDAR spatial features with the WRD attribute information that users have acquired from ICOLD. Despite this limit, GeoDAR, with a dam quantity triple that of GRanD, significantly enhances the spatial details of smaller but more widespread dams and reservoirs and complements other existing global dam inventories. Along with its extended attribute accessibility, GeoDAR is expected to benefit a broad range of applications in hydrologic modeling, water resource management, ecosystem health, and energy planning. [ABSTRACT FROM AUTHOR]

• A generic framework is proposed for classifying freshwater and saline lake typology. • The framework leverages hydroclimate, remote sensing, and literature evidence. • The method is largely based on open-access data requiring no additional field measures. • Lake typology results in the Tibetan Plateau and Australia show promising accuracies. • The framework demonstrates potential for performing a global-scale lake classification. Separating saline and freshwater lakes is of immense importance for monitoring lentic ecosystems and assessing surface freshwater availability. However, conventional lake typology often relies on in situ salinity measurements, thus limiting the feasibility of a global application. To enable an effective workaround, we here propose and test a framework that classifies saline and freshwater lakes through systematic, integrated leveraging of hydrological, climatological, spectral, and literature evidence. In principle, saline lakes were sequentially identified if a lake is (1) located at the drainage terminal where salinity tends to build up as a result of lacking surface outflow (hydrological evidence), (2) distributed in an arid/semiarid climate with lacustrine evaporites visible from a high-resolution multispectral image (climatological and spectral evidence), or (3) documented to be (sub)saline or have measured salinity exceeding the maximum freshwater threshold (literature evidence). We applied the HydroSHEDS hydrography dataset, the Köppen-Geiger climate classification, and a large volume of spectral satellite images and literature to implement this framework. This framework was tested on the Tibetan Plateau using the Landsat-based, 30-m-resolution UCLA Circa-2015 global lake mask, and the result was benchmarked against the Chinese national lake survey. Our collected literature shows a 95% agreement between the lake types classified using hydrological, climatological, and spectral evidence alone and those documented in the literature. After further corrections based on the literature evidence, our final classification reached an overall accuracy of nearly 70% in terms of lake count and 94% in lake area, implying that the efficacy of our method tends to favor relatively large lakes. Given such promising accuracies, we further applied our framework to Australia, showcasing its effectiveness for lake typology classification without additional in situ surveys across the world's most saline continent. While our method, in theory, results in a conservative recognition of saline lakes and should not be considered a complete substitute for in situ surveys, the proposed framework demonstrates potential for performing global-scale freshwater and saline lake typology classification with reasonable accuracies, using only remote sensing images, open-source hydrography and climate data, and existing literature. [ABSTRACT FROM AUTHOR]

Drainage reorganization generally occurs on geological time scales under unstable river network conditions. A few local‐scale studies indicate that recent climatic changes might accelerate the drainage reorganization process. However, large‐scale drainage reorganization during the modern era is rarely documented. This study examines ongoing drainage reorganization on the endorheic Tibetan Plateau (TP) as a primary result of drastic lake expansion. A total of 11 drainage system reorganization events comprising 24 different lake basins and covering a total area of 61,115 km2 occurred between 2000 and 2018. Assuming the continued growth rate of TP lakes, we project another 20 basins will be reorganized before 2030. These drainage basin reorganizations not only alter hydrological processes in the endorheic TP but may also cause the endorheic‐exorheic transition, leading to the upstream sprawl of the Yangtze River Basin and posing outburst flooding risks on China's key infrastructure such as the Qinghai‐Tibet Railway. Plain Language Summary: Recent climatic changes have intensified the global hydrologic cycle, and have likely accelerated drainage system evolution. We have provided a holistic picture of ongoing drainage reorganization driven by drastic lake expansions on the Tibetan Plateau (TP). Our results indicate that 24 different lake drainage systems have undergone reorganization between 2000 and 2018, and the number of basins is expected to increase to 44 by the year 2030. One notable drainage reorganization is between the endorheic Lake Yanhu and the exorheic Chumaer river, resulting in the upstream expansion of the Yangtze River Basin. These findings provide an increased understanding of ongoing drainage reorganization events driven by climatic changes. Further, this work advances our understanding of the connections between ongoing hydrologic changes and their effect on related geological disasters (e.g., outburst floods) within the TP. Key Points: Rapid lake growths drive large‐scale drainage reorganizations on the Tibetan Plateau24 lake drainage systems have undergone reorganization from 2000 to 2018 and this number is expected to increase to 44 by the year 2030The northern portion of the upstream Yangtze basin has expanded by around 8,400 km2 due to an endorheic‐exorheic transition [ABSTRACT FROM AUTHOR]

Abstract: Located in southwestern Inner Mongolia in northern China, the Ulan Buh Desert (UBD) has evolved significantly during the Holocene. The northern desert is adjacent to Hetao Plain, an important agriculture area since the Han Dynasty (~200B.C.). A series of aeolian sand–lacustrine sequences from the desert were measured and dated by using differential global positioning system (DGPS) and optically stimulated luminescence (OSL) technologies respectively. These lacustrine remains with similar deposit sequences have almost identical elevations and depositional ages, indicating that they belonged to a unified paleolake. In addition, the Holocene paleolake/desert evolution process in UBD is established. Aeolian activity prevailed before ~8.3ka, and a unified Ulan Buh Paleolake containing the modern Jilantai Salt Lake covered the northern desert during 7.8–7.1ka ago. The paleolake shrank and broke apart after 6.5ka ago. Thereafter, the paleolake evolved into the modern UBD and Jilantai Salt Lake. The study of one sand–lacustrine section at the southern edge of Hetao Plain shows that the Tushenze Paleolake had a similar evolution process to Ulan Buh Paleolake, though they may not be connected to each other, as suggested by the elevation difference. The Ulan Buh desert–lake evolution was likely due to the climate changes in the monsoon-influenced region during the early–middle Holocene. [Copyright &y& Elsevier]

Winds, wind waves, and turbulence are essential variables and playing critical role in regulating a series of physical and biogeochemical processes in large shallow lakes. However, parameterizing winds, waves, currents and turbulence and simulating the interaction between them in large shallow lakes haven't been evaluated strictly because of a lack of field observations of lake hydrodynamics process. To address this problem, two process-based field observations were conducted to record the development of summer and winter wind-driven currents in Lake Taihu, a large shallow lake in China. Based on these observations and numerical experiments, a wave-current coupled model (WCCM) is developed by rebuilding expression of wind drag coefficient, introducing wave-induced radiation stress, and adopting a simple turbulence scheme, and then used to simulate wind-driven currents in Lake Taihu. The results show that, the WCCM can accurately simulate the upwelling process resulting from the wind-driven currents during the field observations. Comparing with other model, there is a 42.9 % increase of WCCM-simulated current speed which is mainly attributed to the new expression of wind drag coefficient. Meanwhile WCCM-simulated current direction and field are also improved due to the introduction of wave-induced radiation stress. Furthermore, the use of the simple turbulent scheme in the WCCM makes the simulation of the upwelling processes more efficient. The WCCM provides a sound basis for simulating shallow lake ecosystems. [ABSTRACT FROM AUTHOR]

The lower parts of two glaciers in the Aru range on the western Tibetan Plateau (TP) collapsed on 17 July and 21 September 2016, respectively, causing fatal damage to local people and their livestock. The giant ice avalanches, with a total volume of 150 × 10 6 m 3 , had almost melted by September 2019 (about 30 % of the second ice avalanche remained). The impact of these extreme disasters on downstream lakes has not been investigated yet. Based on in situ observation, bathymetry survey and satellite data, we explore the impact of the ice avalanches on the two downstream lakes (i.e., Aru Co and Memar Co) in terms of lake morphology, water level and water temperature in the subsequent 4 years (2016–2019). After the first glacier collapse, the ice avalanche slid into Aru Co along with a large amount of debris, which generated great impact waves in Aru Co and significantly modified the lake's shoreline and underwater topography. An ice volume of at least 7.1 × 10 6 m 3 was discharged into Aru Co, spread over the lake surface and considerably lowered its surface temperature by 2–4 ∘ C in the first 2 weeks after the first glacier collapse. Due to the large amount of meltwater input, Memar Co exhibited more rapid expansion after the glacier collapses (2016–2019) than before (2003–2014), in particular during the warm season. The melting of ice avalanches was found to contribute to about 23 % of the increase in lake storage between 2016 and 2019. Our results indicate that the Aru glacier collapses had both short-term and long-term impacts on the downstream lakes and provide a baseline in understanding the future lake response to glacier melting on the TP under a warming climate. [ABSTRACT FROM AUTHOR]

Protected areas (PAs) have been established worldwide for achieving long-term goals in the conservation of nature with the associated ecosystem services and cultural values. Globally, 15% of the world's terrestrial lands and inland waters, excluding Antarctica, are designated as PAs. About 4.12% of the global ocean and 10.2% of coastal and marine areas under national jurisdiction are set as marine protected areas (MPAs). Protected lands and waters serve as the fundamental building blocks of virtually all national and international conservation strategies, supported by governments and international institutions. Some of the PAs are the only places that contain undisturbed landscape, seascape and ecosystems on the planet Earth. With intensified impacts from climate and environmental change, PAs have become more important to serve as indicators of ecosystem status and functions. Earth's remaining wilderness areas are becoming increasingly important buffers against changing conditions. The development of remote sensing platforms and sensors and the improvement in science and technology provide crucial support for the monitoring and management of PAs across the world. In this editorial paper, we reviewed research developments using state-of-the-art remote sensing technologies, discussed the challenges of remote sensing applications in the inventory, monitoring, management and governance of PAs and summarized the highlights of the articles published in this Special Issue. [ABSTRACT FROM AUTHOR]

The Slumgullion landslide, located in southwestern Colorado, has been active since the early 1700s and current data suggests that the most active portion of the slide creeps at a rate of ~1.5–2.0 cm/day. Accurate deformation measurement techniques are vital to the understanding of persistent, yet slow-moving landslides like the Slumgullion. The factors that affect slope movements at the Slumgullion are on-time scales that are well suited towards a remotely sensed approach to constrain the 12 different kinematic units that make up the persistent creeping landslide. We derive a time series of motion vectors (magnitude and direction) using subpixel offset techniques from very high resolution TerraSAR-X Staring Spotlight ascending/descending data as well as from a novel high-resolution amalgamation of airborne lidar and unmanned aerial systems (UAS) Structure from Motion (SfM) digital surface model (DSM) hillshades. Deformation rates calculated from the spaceborne and airborne datasets show high agreement (mean difference of ~0.9 mm/day), further highlighting the potential for the monitoring of ongoing mass wasting events utilizing unmanned aircraft systems (UAS) We compare pixel offset results from an 11-day synthetic aperture radar (SAR) pair acquired in July of 2016 with motion vectors from a coincident low-cost L1 only Global Navigation Satellite System (GNSS) field campaign in order to verify the remotely sensed results and to derive the accuracy of the azimuth and range offsets. We find that the average azimuth and range pixel offset accuracies utilizing the methods herein are on the order of 1/18 and 1/20 of their along-track and slant range focused ground pixel spacing values of 16.8 cm and 45.5 cm, respectively. We utilize the SAR offset time series to add a twelfth kinematic unit to the previously established set of eleven unique regions at the site of an established minislide within the main landslide itself. Lastly, we compare the calculated rates and direction from all spaceborne- and airborne-derived motion vectors for each of the established kinematic zones within the active portion of the landslide. These comparisons show an overall increased magnitude and across-track component (i.e., more westerly angles of motion) for the descending SAR data as compared to their ascending counterparts. The processing techniques and subsequent results herein provide for an improved knowledge of the Slumgullion landslide's kinematics and this increased knowledge has implications for the advancement of measurement techniques and the understanding of globally distributed creeping landslides. [ABSTRACT FROM AUTHOR]

Abstract Lakes are sensitive indicators of anthropogenic climate change and also respond to direct human activities. Yet, long-term lake inventories and quantitative evaluation of the factors driving observed lake changes across China remain elusive. Here, for the first time, we examined multi-decadal lake area changes in China during 1960s–2015, using historical topographic maps and >3831 Landsat satellite images, including lakes as fine as ≥1 km2 in size. In addition, we quantified the causes of lake changes from climatic and anthropogenic factors. The total area of lakes in China has increased by 5858.06 km2 (9%) between 1960s and 2015, and with heterogeneous spatial variations. Lake area changes in the Tibetan Plateau, Xinjiang, and Northeast Plain and Mountain regions reveal significant increases of 5676.75, 1417.15, 1134.87 km2 (≥15%), respectively, but the Inner-Mongolian Plateau shows an obvious decrease of 1223.76 km2 (22%). We find that 141 new lakes have appeared predominantly in the arid western China; but 333 lakes, mainly located in the humid eastern China, have disappeared over the past five decades. We conclude that climate factors have played a dominant role in lake changes across China, coupled with noticeable anthropogenic contribution of ~35% in the Eastern Plain and Yunnan-Guizhou Plateau. This study has substantial implications to improve decision support regarding water-resource management strategies and land-use planning throughout China. Highlights • Produced a comprehensive China lake dataset from the 1960s to 2015 • Total lake area increased by 9% over five decades with evident regional differences • New lakes and lake area expansion in the arid western China due to climate change • Disappeared and shrinking lakes in the humid eastern China due to human activity [ABSTRACT FROM AUTHOR]

Glacial lake outburst floods (GLOFs) are a unique type of natural hazard in the cryosphere that may result in catastrophic fatalities and damages. The Himalayas are known as one of the world's most GLOF-vulnerable zones. Effective hazard assessments and risk management require a thorough inventory of historical GLOF events across the Himalayas, which is hitherto absent. Existing studies imply that numerous historical GLOF events are contentious because of discrepant geographic coordinates, names, or outburst time, requiring further verifications. This study reviews and verifies over 60 historical GLOF events across the Himalayas using a comprehensive method that combines literature documentations, archival remote sensing observations, geomorphological analysis, and field investigations. As a result, three unreported GLOF events were discovered from remote sensing images and geomorphological analysis. Eleven suspicious events were identified and suggested to be excluded. The properties of five outburst lakes, i.e., Degaco, Chongbaxia Tsho, Geiqu, Lemthang Tsho, and a lake on Tshojo Glacier, were corrected or updated. A total of 51 GLOF events were verified to be convincing, and these outburst lakes were classified into three categories according to their statuses in the past decades, namely disappeared (12), stable (30), and expanding (9). Statistics of the verified GLOF events show that GLOF tended to occur between April and October in the Himalayas. We suggest that more attention should be paid to rapidly expanding glacial lakes with high possibility of repetitive outbursts. This study also demonstrates the effectiveness of integrating remote sensing and geomorphic interpretations in identifying and verifying GLOF events in remote alpine environments. This inventory of GLOFs with a range of critical attributes (e.g., locations, time, and mechanisms) will benefit the continuous monitoring and prediction of potentially dangerous glacial lakes and contribute to outburst-induced risk assessments and hazard mitigations. [ABSTRACT FROM AUTHOR]

The water balance of inland lakes on the Tibetan Plateau (TP) involves complex hydrological processes; their dynamics over recent decades is a good indicator of changes in water cycle under rapid global warming. Based on satellite images and extensive field investigations, we demonstrate that a coherent lake growth on the TP interior (TPI) has occurred since the late 1990s in response to a significant global climate change. Closed lakes on the TPI varied heterogeneously during 1976-1999, but expanded coherently and significantly in both lake area and water depth during 1999-2010. Although the decreased potential evaporation and glacier mass loss may contribute to the lake growth since the late 1990s, the significant water surplus is mainly attributed to increased regional precipitation, which, in turn, may be related to changes in large-scale atmospheric circulation, including the intensified Northern Hemisphere summer monsoon (NHSM) circulation and the poleward shift of the Eastern Asian westerlies jet stream. [ABSTRACT FROM AUTHOR]

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. • Constrained glacier mass changes in the inner TP based on InSAR-derived global DEMs. • Comprehensive basin-scale estimates of glacier/lake mass changes and the ratio. • Overall minimal but highly variable contribution of glaciers to Tibetan lake growth. [ABSTRACT FROM AUTHOR]

Summary: Although lakes on the central Tibetan Plateau (TP) expanded significantly in recent decades, causes for the lake growth still have not been well addressed. Based on remote sensing and GIS techniques together with bathymetric survey and water balance analysis, we show how climatic changes and glacier mass loss have influenced the inland lake dynamics on the central TP. Our results show that six closed lakes (Siling Co, Nam Co, Bam Co, Pung Co, Darab Co and Zige Tangco) expanded by 20.2% in area, by 8.7m in water depth, and by 37.7Gt in the total storage between 1976 and 2010, with a remarkable acceleration after 1999. The growth rate of lake area, water level and storage between 1999 and 2010 was 5.0, 3.6 and 4.8 times, respectively, than that between 1976 and 1999, corresponding well with the significant climatic changes in the late 1990s. Water balance analysis shows that increased precipitation and runoff, and decreased lake evaporation were the main causes for the coherent lake growth and could contribute by about 70% of total increase in lake storage. Based on modern mass balance results , glacier mass loss between 1999 and 2010 was estimated to contribute to the lake level rise of the three glacial-fed lakes, Siling Co, Nam Co and Pung Co, by ∼1.0m, ∼0.7m and ∼1.1m, respectively, accounting for 11.7%, 28.7% and 11.4% of the total lake level rise. [ABSTRACT FROM AUTHOR]

Four wetland maps for all China have been produced, based on Landsat and CBERS-02B remote sensing data between 1978 and 2008 (1978, 1990, 2000 and 2008). These maps were mainly developed by manual interpretation and validated by substantial field investigation in 2009. Based on these maps, we analyzed the 2008 wetland distribution in China and discussed wetland changes and their drivers over the past 30 years. (i) There were about 324097 km of wetlands in 2008, for which inland marshes or swamps were the most common wetland type (35%), with lakes (26%) second. Most of the wetlands were in Heilongjiang, Inner Mongolia, Qinghai and Tibet, occupying about 55% of the national wetland area. (ii) From 1978 to 2008, China's wetland area continually and significantly decreased, by about 33% based on changes in the wetland map. This was in sharp contrast to the increase in artificial wetlands, which increased by about 122%. Inland marshes accounted for the main loss of total wetlands from 1978 to 2000. From 2000 through 2008, riverine and lacustrine wetlands constituted the main wetland loss. Fortunately however, the rate of wetland loss decreased from 5523 to 831 km/a. (iii) The change ratio of lost natural wetlands (including inland and coastal wetlands) to non-wetlands has decreased slightly over the past 30 years. From 1978 to 1990, nearly all natural wetlands (98%) lost were transformed into non-wetlands. However, the ratio declined to 86% from 1990 to 2000, and to 77% from 2000 to 2008. (iv) All Chinese provinces were divided into three groups according to patterns of wetland changes, which could relate to the driving forces of such changes. Tibet was completely different from other provinces, as it was one representative example in which there was a net wetland increase, because of global warming and decreased human activity since 1990. Increased economic development caused considerable wetland loss in most eastern provinces, and artificial wetlands increased. [ABSTRACT FROM AUTHOR]

The planned Surface Water and Ocean Topography (SWOT) satellite mission will measure freshwater storage changes in global lakes. Herein, the anticipated SWOT storage change accuracy is evaluated for the lakes in the Peace-Athabasca Delta, Northern Alaska and Western Siberia. Because of the significant lack of Arctic lake measurements, we simulated realistic daily to seasonal changes in water elevations in the study region using a combination of data from lake gauges, satellite radar altimeter, and satellite imagery. This 'truth' dataset is sampled with several candidate SWOT orbits and then corrupted with expected instrument errors to simulate SWOT observed storage changes. The number of revisits increases with increasing or decreasing latitude for a given repeat cycle (e.g. four to eight revisits for a 22-day cycle), allowing us to investigate storage change errors at monthly sampling. SWOT storage change accuracy is primarily controlled by lake size. Lakes larger than 1 km2 have relative errors generally less than 5% whereas one-hectare size lakes are about 20%. We concluded that the storage change accuracy is insensitive to the orbital inclination or repeat periods, but is sensitive to lake shapes. [ABSTRACT FROM AUTHOR]

It is unclear whether the Holocene climatic optimum (HCO) occurred synchronously throughout the East Asian summer monsoon (EASM) region, and if it did, whether it occurred in the early Holocene (EH, 11.7–8.0 ka, ka = 1000 years before present, where the "present" is defined as the year CE 1950), or in the middle Holocene (MH, 8.0–4.0 ka). This is because the definition of the HCO in previous paleoclimatic studies was mainly based on the criterion of maximum temperature or some "optimum" combination of temperature and precipitation. Since the development of prehistoric societies and human welfare are closely linked to climatic variability, it may be more meaningful to define the HCO from the perspective of climatic stability, which may provide fresh insight into the debate on the timing of the HCO. Here we use calculations of squared chord distance (SCD), an effective method for quantifying temporal dissimilarity of the variance of samples in a time series, to quantitatively compare the climatic stability of the EH and the MH, based on a diverse range of the EASM-associated paleoclimatic records from the EASM region. The results show that the SCD values decreased significantly from the EH to the MH, indicating a more stable climate which occurred synchronously during the MH in the EASM region. We suggest that the stable climate of the MH provided an optimum environment for the development of agriculture and animal husbandry, which contributed to rapid population growth and the flourishing of the Yangshao culture which was the most prosperous Neolithic culture in the EASM region of China during the Holocene. Thus we propose that the stable MH climate can be used to define a synchronous HCO of the EASM which was more supportive of societal development and population growth than that during the EH. The results of TraCE-21 ka climatic modeling reveal that, with the retreat of the Northern Hemisphere ice sheets, the variability of the westerly jet (WJ), which was previously perturbed by large ice sheets, was significantly reduced from the EH to the MH. This reduced WJ variability during the MH enhanced the stability of the climate of the EASM region, via the interactions of the EASM and the WJ. [ABSTRACT FROM AUTHOR]

The deposition of suspended sediment is an important process that helps wetlands accrete surface material and maintain elevation in the face of sea level rise. Optical remote sensing is often employed to map total suspended solids (TSS), though algorithms typically have limited transferability in space and time due to variability in water constituent compositions, mixtures, and inherent optical properties. This study used in situ spectral reflectances and their first derivatives to compare empirical algorithms for estimating TSS using hyperspectral and multispectral data. These algorithms were applied to imagery collected by NASA's Airborne Visible/Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) over coastal Louisiana, USA, and validated with a multiyear in situ dataset. The best performing models were then applied to independent spectroscopic data collected in the Peace–Athabasca Delta, Canada, and the San Francisco Bay–Delta Estuary, USA, to assess their robustness and transferability. A derivative-based partial least squares regression (PLSR) model applied to simulated AVIRIS-NG data showed the most accurate TSS retrievals (R2 = 0.83) in these contrasting deltaic environments. These results highlight the potential for a more broadly applicable generalized algorithm employing imaging spectroscopy for estimating suspended solids. [ABSTRACT FROM AUTHOR]