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Guido Grosse - One of the best experts on this subject based on the ideXlab platform.
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Distribution of Thermokarst Lakes and Ponds at Three Yedoma Sites in Siberia
2020Co-Authors: Guido Grosse, Vladimir E. Romanovsky, K. M. Walter, Anne Morgenstern, Hugues Lantuit, Sergei ZimovAbstract:Thermokarst Lake formation in ice-rich yedoma deposits in north Siberia has a major impact on regional landscape morphology, hydrology, and biogeochemistry. Detailed assessment of Lake distribution characteristics is critical for understanding spatial and temporal Lake Dynamics and quantifying their impacts. The distribution of thermokarst ponds and Lakes at three different sites with ice-rich permafrost (Bykovsky Peninsula, SW Lena Delta, and Cherskii) in northeast Siberia was analysed using high-resolution remote sensing and geographical information system (GIS) tools. Despite similarities in geocryological characteristics, the distribution of thermokarst Lakes differs strongly among the study regions and is heavily influenced by the overall hydrological and geomorphologic situation as a result of past Lake-landscape Dynamics. By comparing our high-resolution water body dataset with existing Lake inventories, we find major discrepancies in Lake distribution and total coverage. The use of low-resolution Lake inventories for upscaling of thermokarst Lake-related environmental processes like methane emissions would result in a strong underestimation of the environmental impacts of thermokarst Lakes and ponds in Arctic lowlands.
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Thermokarst Lakes, drainage, and drained basins
Treatise on Geomorphology, 2020Co-Authors: Guido Grosse, Benjamin M JonesAbstract:Thermokarst Lakes and drained Lake basins are widespread in Arctic and sub-Arctic permafrost lowlands with ice-rich sediments. Thermokarst Lake formation is a dominant mode of permafrost degradation and is linked to surface disturbance, subsequent melting of ground ice, surface subsidence, water impoundment, and positive feedbacks between Lake growth and permafrost thaw, whereas Lake drainage generally results in local permafrost aggradation. Thermokarst Lakes characteristically have unique limnological, morphological, and biogeochemical characteristics that are closely tied to cold-climate conditions and permafrost properties. Thermokarst Lakes also have a tendency toward complete or partial drainage through permafrost degradation and erosion. Thermokarst Lake Dynamics strongly affect the development of landscape geomorphology, hydrology, and the habitat characteristic of permafrost lowlands.
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Past and present thermokarst Lake Dynamics in the Yedoma Ice Complex region of North-Eastern Yakutia
2018Co-Authors: Alexandra Veremeeva, Ingmar Nitze, Guido Grosse, Frank Günther, Nadezhda Glushkova, Elizaveta RivkinaAbstract:Thermokarst Lakes are typical components of the yedoma-alas dominated relief in the coastal lowlands of North- Eastern Yakutia and formed as a result of thawing Late Pleistocene ice-rich Yedoma Ice Complex (IC) deposits. The aim of our study is to estimate thermokarst Lake area changes from the early Holocene onwards based on RS data. The decrease of thermokarst Lake area from the early Holocene, taking into account total alas depression areas, is as much as 81-83 %. Modern climate warming has led to a general trend of thermokarst Lake area decrease. Lake drainage occurs mostly on elevated sites with high Yedoma IC fraction while Lake area increase is typical for low-lying areas with a small Yedoma IC fraction. The area increase of thermokarst ponds on flat, boggy yedoma surfaces indicates ice wedge degradation in response to rising summer air temperatures and precipitation.
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Thermokarst Lake monitoring on the Bykovsky Peninsula using high-resolution remote sensing data
2018Co-Authors: Theresa Henning, Frank Günther, A.i. Kizyakov, Guido GrosseAbstract:Thermokarst Lakes are a characteristic element of arctic permafrost regions and an indicator for their rapid landscape changes. Assessing their Dynamics contributes to the understanding of driving processes of change, to the evaluation of impacts on landscape characteristics as well as to the estimation of the impact on the permafrost-related carbon budget. Monitoring thermokarst Lake Dynamics on the Bykovsky Peninsula, consisting of ice-rich Yedoma deposits, using high resolution remote sensing imagery from 1951 to 2016, revealed a long-term tendency towards Lake drainage. Approximately 17% of the 1951 Lake area was lost due to coastal erosion or the development of drainage networks. In parallel, coastal erosion driven land loss amounts to 2.3% of the peninsula. We find process interconnections between coastal erosion and Lake change, as well as Lake change dependency on land elevation in a developed alas-yedoma thermokarst relief.
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Thermokarst Lake Dynamics and its influence on biogeochemical sediment characteristics: A case study from the discontinuous permafrost zone in Interior Alaska
2017Co-Authors: Josefine Lenz, Katey M. Walter Anthony, Christopher V. Maio, Filip Matuszewski, Guido GrosseAbstract:Under the currently projected scenarios of a warming climate, discontinuous and warm permafrost in Interior Alaska is expected to experience dramatic thinning. Thermokarst ponds and Lakes give evidence for permafrost thaw and, vice versa, amplify deep thaw by talik development. During the thawing process, previously preserved organic matter is decomposed and potentially released as greenhouse gases carbon dioxide and methane. In the course of Lake development and shoreline expansion, both, younger near-surface and older organic matter from slumping shores are potentially deposited in the Lake basin. Lake internal bioproductivity is complementing carbon accumulation in lacustrine deposits and provides an additional source of young carbon transformed into greenhouse gases. This study presents results of two intersecting, limnolithological transects of 5 sediment cores from Goldstream Lake, a typical small, boreal thermokarst Lake in Interior Alaska. With the aim to distinguish external terrestrial and internal aquatic carbon contributions to sediments, sediment samples are analyzed for the total organic carbon/total nitrogen ratio (C/N) as well as stable carbon isotopes. Selected samples are analyzed for their grain size distribution in order to reconstruct the depositional environment and accumulation conditions. The littoral zone with actively eroding shorelines is characterized by methane bubbles produced from anaerobic microbial decomposition but near-shore sediments have surprisingly low total organic carbon contents of mean 1.5 wt%; the low C/N ratio of 8.7 indicate a dominance of lacustrine plant material. Very similar results are found for sediments in the central basin but a clear shift to a terrestrial carbon signal (C/N of 22) with total organic carbon content of almost 30 wt% is presumably indicating the trash layer of the initial Lake phase. The talik sediments seem to have carbon storage as low as the Lake sediments but are not as well layered. Subarctic aquatic environments like Goldstream Lake demonstrate a relatively low aquatic productivity and a high biogeochemical turn-over over short periods of time. In addition, the ongoing decomposition of organic matter in talik sediments proves to be crucial to assess the contribution of thermokarst Lakes to future climate change by mobilizing Ice Age soil carbon previously frozen in permafrost.
Benjamin M Jones - One of the best experts on this subject based on the ideXlab platform.
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Thermokarst Lakes, drainage, and drained basins
Treatise on Geomorphology, 2020Co-Authors: Guido Grosse, Benjamin M JonesAbstract:Thermokarst Lakes and drained Lake basins are widespread in Arctic and sub-Arctic permafrost lowlands with ice-rich sediments. Thermokarst Lake formation is a dominant mode of permafrost degradation and is linked to surface disturbance, subsequent melting of ground ice, surface subsidence, water impoundment, and positive feedbacks between Lake growth and permafrost thaw, whereas Lake drainage generally results in local permafrost aggradation. Thermokarst Lakes characteristically have unique limnological, morphological, and biogeochemical characteristics that are closely tied to cold-climate conditions and permafrost properties. Thermokarst Lakes also have a tendency toward complete or partial drainage through permafrost degradation and erosion. Thermokarst Lake Dynamics strongly affect the development of landscape geomorphology, hydrology, and the habitat characteristic of permafrost lowlands.
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landsat based trend analysis of Lake Dynamics across northern permafrost regions
Remote Sensing, 2017Co-Authors: Ingmar Nitze, Guido Grosse, Benjamin M Jones, Mathias Ulrich, Alexander N Fedorov, Alexandra VeremeevaAbstract:Lakes are a ubiquitous landscape feature in northern permafrost regions. They have a strong impact on carbon, energy and water fluxes and can be quite responsive to climate change. The monitoring of Lake change in northern high latitudes, at a sufficiently accurate spatial and temporal resolution, is crucial for understanding the underlying processes driving Lake change. To date, Lake change studies in permafrost regions were based on a variety of different sources, image acquisition periods and single snapshots, and localized analysis, which hinders the comparison of different regions. Here, we present a methodology based on machine-learning based classification of robust trends of multi-spectral indices of Landsat data (TM, ETM+, OLI) and object-based Lake detection, to analyze and compare the individual, local and regional Lake Dynamics of four different study sites (Alaska North Slope, Western Alaska, Central Yakutia, Kolyma Lowland) in the northern permafrost zone from 1999 to 2014. Regional patterns of Lake area change on the Alaska North Slope (−0.69%), Western Alaska (−2.82%), and Kolyma Lowland (−0.51%) largely include increases due to thermokarst Lake expansion, but more dominant Lake area losses due to catastrophic Lake drainage events. In contrast, Central Yakutia showed a remarkable increase in Lake area of 48.48%, likely resulting from warmer and wetter climate conditions over the latter half of the study period. Within all study regions, variability in Lake Dynamics was associated with differences in permafrost characteristics, landscape position (i.e., upland vs. lowland), and surface geology. With the global availability of Landsat data and a consistent methodology for processing the input data derived from robust trends of multi-spectral indices, we demonstrate a transferability, scalability and consistency of Lake change analysis within the northern permafrost region.
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Understanding Thermokarst Lake Dynamics in Arctic Alaska: Case Studies based on Sediment Cores
2015Co-Authors: Josefine Lenz, Benjamin M Jones, Sebastian Wetterich, Guido GrosseAbstract:Arctic landscape Dynamics are an indicator of long-term natural processes. Within the Arctic system, permafrost-related processes are key ecosystem drivers and influence regional landscape evolution, hydrology, etc. Thermokarst Lake Dynamics, involving initiation, expansion, drainage, and re-initiation, have reshaped vast Arctic lowlands in Siberia, Alaska, and Canada since the last deglaciation (~15,000 years ago). Today, thermokarst Lakes across the circum-Arctic are responding quite variably to a warming. A multitude of remote sensing studies reports on losses in thermokarst Lake area due to increased evapotranspiration and drying or rapid Lake drainage, while increased thermokarst Lake formation is reported from more northern regions. To understand these modern Dynamics and place observations into a long-term context it is necessary to understand the paleoDynamics of thermokarst Lakes. A useful technique to achieve this is the use of core-based reconstructions of paleoenvironmental conditions during the Lake history using various sedimentological, biogeochemical, and biological proxies. We applied a multi-proxy approach on sediment cores making use of methods in sedimentology (grain size analyses, magnetic susceptibility), biogeochemistry (TN, TC, TOC, δ13C), geochronology (14C, tephra chronology), and micropaleontology (ostracods, rhizopods). Our studies on modern but also recently drained basins in Arctic Alaska (USA) are based on sediment cores from the northern Seward Peninsula and the Teshekpuk Lake region and provide insights into past landscape Dynamics since the late Pleistocene in these continuous permafrost regions. GG basin on the northern Seward Peninsula, shown in the figure below, drained in spring 2005. Its Lake initiation was radiocarbon-dated to about 300 years before present (BP) and was indicated by freshwater ostracods (e.g. Fabaeformiscandina protzi) and hydrophilic rhizopods (e.g. Cyclopyxis kahli). Before this, ice-rich silty and organic-rich sediments known as yedoma deposits accumulated during cold and dry conditions of the Late Mid-Wisconsin. An intermediate peaty layer with hydrophilic rhizopods indicates wet conditions from 44.5-41.5 ka BP. This possibly first thermokarst development was interrupted by a 1 m thick layer of tephra which could be associated with the South Killeak Maar eruption around 42 ka BP. As observed by satellite images, the modern Lake drained between May and June 2015 possible due to increased discharge by thawing of snow which was possibly also blocking the outlet. Permafrost redeveloped since then from the surface down to 270 cm depth. Our investigations demonstrate that Lake development in the permafrost-affected terrestrial Arctic can be triggered but also interrupted by global climate change (e.g. rapid warming and wetting in the Holocene), by regional environmental Dynamics (e.g. nearby volcanic eruptions and tephra deposition) or by local disturbance processes (e.g. Lake drainage). We found that Arctic Lake systems and periglacial landscapes were sensitive to rapid change in the past. Field and remote sensing observations show that thermokarst Lakes are vulnerable to rapid change in the present. Thus most likely thermokarst Lake Dynamics will have an important role for landscape and ecosystem change in a warming Arctic during the Anthropocene.
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modern thermokarst Lake Dynamics in the continuous permafrost zone northern seward peninsula alaska
Journal of Geophysical Research, 2011Co-Authors: Guido Grosse, Benjamin M Jones, Miriam C Jones, K Walter M Anthony, V E RomanovskyAbstract:[1] Quantifying changes in thermokarst Lake extent is of importance for understanding the permafrost-related carbon budget, including the potential release of carbon via Lake expansion or sequestration as peat in drained Lake basins. We used high spatial resolution remotely sensed imagery from 1950/51, 1978, and 2006/07 to quantify changes in thermokarst Lakes for a 700 km2 area on the northern Seward Peninsula, Alaska. The number of water bodies larger than 0.1 ha increased over the entire observation period (666 to 737 or +10.7%); however, total surface area decreased (5,066 ha to 4,312 ha or −14.9%). This pattern can largely be explained by the formation of remnant ponds following partial drainage of larger water bodies. Thus, analysis of large Lakes (>40 ha) shows a decrease of 24% and 26% in number and area, respectively, differing from Lake changes reported from other continuous permafrost regions. Thermokarst Lake expansion rates did not change substantially between 1950/51 and 1978 (0.35 m/yr) and 1978 and 2006/07 (0.39 m/yr). However, most Lakes that drained did expand as a result of surface permafrost degradation before lateral drainage. Drainage rates over the observation period were stable (2.2 to 2.3 per year). Thus, analysis of decadal-scale, high spatial resolution imagery has shown that Lake drainage in this region is triggered by lateral breaching and not subterranean infiltration. Future research should be directed toward better understanding thermokarst Lake Dynamics at high spatial and temporal resolution as these systems have implications for landscape-scale hydrology and carbon budgets in thermokarst Lake-rich regions in the circum-Arctic.
Tak Shun D Tong - One of the best experts on this subject based on the ideXlab platform.
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monitoring decadal Lake Dynamics across the yangtze basin downstream of three gorges dam
Remote Sensing of Environment, 2014Co-Authors: Jida Wang, Yongwei Sheng, Tak Shun D TongAbstract:Abstract The Yangtze River Basin downstream of China's Three Gorges Dam (TGD) (thereafter referred to as “downstream” basin) hosts the largest cluster of freshwater Lakes in East Asia. These Lakes are crucial water stocks to local biophysical environments and socioeconomic development. Existing studies document that individual Lakes in this region have recently experienced dramatic changes under the context of enduring meteorological drought, continuous population growth, and extensive water regulation since TGD's initial impoundment (i.e., June, 2003). However, spatial and temporal patterns of Lake Dynamics across the complete downstream Yangtze basin remain poorly characterized. Using daily MODIS imagery and an advanced thematic mapping scheme, this study presents a comprehensive monitoring of area Dynamics in the downstream Lake system at a 10-day temporal resolution during 2000–2011. The studied Lakes constitute ~ 76% (~ 11,400 km2) of the total downstream Lake area, including the entire + 70 major Lakes larger than 20 km2. The results reveal a decadal net decline in Lake inundation area across the downstream Yangtze Basin, with a cumulative decrease of 849 km2 or 7.4% from 2000 to 2011. Despite an excessive precipitation anomaly in the year 2010, the decreasing trend was tested significant in all seasons. The most substantial decrease in the post-TGD period appears in fall (1.1% yr− 1), which intriguingly coincides with the TGD water storage season. Regional Lake Dynamics exhibit contrasting spatial patterns, manifested as evident decrease and increase of aggregated Lake areas respectively within and beyond the Yangtze Plain. This contrast suggests a marked vulnerability of Lakes in the Yangtze Plain, to not only local meteorological variability but also intensified human water regulations from both the upstream Yangtze main stem (e.g., the TGD) and tributaries (e.g., Lakes/reservoirs beyond the Yangtze Plain). The produced Lake mapping result and derived Lake area Dynamics across the downstream Yangtze Basin provides a crucial monitoring basis for continuous investigations of changing mechanisms in the Yangtze Lake system.
Yongwei Sheng - One of the best experts on this subject based on the ideXlab platform.
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Contrasting evolution patterns between glacier-fed and non-glacier-fed Lakes in the Tanggula Mountains and climate cause analysis
Climatic Change, 2016Co-Authors: Chunqiao Song, Yongwei ShengAbstract:Abstract 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.
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monitoring decadal Lake Dynamics across the yangtze basin downstream of three gorges dam
Remote Sensing of Environment, 2014Co-Authors: Jida Wang, Yongwei Sheng, Tak Shun D TongAbstract:Abstract The Yangtze River Basin downstream of China's Three Gorges Dam (TGD) (thereafter referred to as “downstream” basin) hosts the largest cluster of freshwater Lakes in East Asia. These Lakes are crucial water stocks to local biophysical environments and socioeconomic development. Existing studies document that individual Lakes in this region have recently experienced dramatic changes under the context of enduring meteorological drought, continuous population growth, and extensive water regulation since TGD's initial impoundment (i.e., June, 2003). However, spatial and temporal patterns of Lake Dynamics across the complete downstream Yangtze basin remain poorly characterized. Using daily MODIS imagery and an advanced thematic mapping scheme, this study presents a comprehensive monitoring of area Dynamics in the downstream Lake system at a 10-day temporal resolution during 2000–2011. The studied Lakes constitute ~ 76% (~ 11,400 km2) of the total downstream Lake area, including the entire + 70 major Lakes larger than 20 km2. The results reveal a decadal net decline in Lake inundation area across the downstream Yangtze Basin, with a cumulative decrease of 849 km2 or 7.4% from 2000 to 2011. Despite an excessive precipitation anomaly in the year 2010, the decreasing trend was tested significant in all seasons. The most substantial decrease in the post-TGD period appears in fall (1.1% yr− 1), which intriguingly coincides with the TGD water storage season. Regional Lake Dynamics exhibit contrasting spatial patterns, manifested as evident decrease and increase of aggregated Lake areas respectively within and beyond the Yangtze Plain. This contrast suggests a marked vulnerability of Lakes in the Yangtze Plain, to not only local meteorological variability but also intensified human water regulations from both the upstream Yangtze main stem (e.g., the TGD) and tributaries (e.g., Lakes/reservoirs beyond the Yangtze Plain). The produced Lake mapping result and derived Lake area Dynamics across the downstream Yangtze Basin provides a crucial monitoring basis for continuous investigations of changing mechanisms in the Yangtze Lake system.
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response of inland Lake Dynamics over the tibetan plateau to climate change
Climatic Change, 2014Co-Authors: Kun Yang, Yongwei Sheng, Bin Wang, Broxton W Bird, Guoqing Zhang, Lide TianAbstract: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 signifi- cantly 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.
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an automated scheme for glacial Lake Dynamics mapping using landsat imagery and digital elevation models a case study in the himalayas
Journal of remote sensing, 2012Co-Authors: Junli Li, Yongwei ShengAbstract: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.
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Automated Image Registration for Hydrologic Change Detection in the Lake-Rich Arctic
IEEE Geoscience and Remote Sensing Letters, 2008Co-Authors: Yongwei Sheng, Chintan A. Shah, Laurence C. SmithAbstract:Multitemporal remote sensing provides a unique tool to track Lake Dynamics at the pan-Arctic scale but requires precise registration of thousands of satellite images. This is a challenging task owing to a dearth of stable features to be used as tie points [(TPs), i.e., control points] in the dynamic landscapes. This letter develops an automated method to precisely register images in the Lake-rich Arctic. The core premise of the method is that the centers of Lakes are generally stable even if their shorelines are not. The proposed procedures first extract Lakes in multitemporal satellite images, derive Lake centroids and match them between images, and then use the centroids of stable Lakes as TPs for image registration. The results show that this approach can achieve subpixel registration accuracy, outcompeting the conventional manual methods in both efficiency and accuracy. The proposed method is fully automated and represents a feasible way to register images for Lake change detection at the pan-Arctic scale.
Jida Wang - One of the best experts on this subject based on the ideXlab platform.
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Lake Dynamics in the Yangtze Basin Downstream of Three Gorges Dam Driven by Natural Determinants and Human Activities
2020Co-Authors: Jida WangAbstract:Author(s): Wang, Jida | Advisor(s): Sheng, Yongwei | Abstract: In the era of "Anthropocene", Lakes as essential stocks of terrestrial water resources are subject to increasing vulnerability from both climate change and human activities. There has been a widespread recognition of the need for further enhancing our monitoring and understanding of Lake Dynamics under complex human-environment interactions, particularly in populated and rapidly developing regions. To address this pressing need, this dissertation highlights the Yangtze River Basin downstream of China's Three Gorges Dam (TGD), one of the world's most populous areas and a critical eco-region, which hosts the largest cluster of freshwater Lakes in East Asia. The TGD, thus far the world's largest hydroelectric project, initiated water impoundment in June, 2003. Existing studies document that individual Lakes in this region have recently experienced dramatic changes under the context of enduring climatic drought, continuous population growth, and extensive human water regulation. However, spatial and temporal patterns of Lake Dynamics across the complete downstream Yangtze basin are poorly characterized; and the underlying changing mechanisms remain largely unclear. With an emphasis of the controversial TGD impacts, this dissertation presents a comprehensive investigation integrating remote sensing, spatial statistics, and hydrological modeling to (1) understand the recent Lake Dynamics across the downstream Yangtze Basin before and after the initial TGD operation and (2) diagnose the driving mechanism from inducing factors of both climatic variability and major anthropogenic activities, i.e., the TGD operation and human water consumption. A widespread net decline in Lake inundation area was revealed across the downstream Yangtze Basin during 2000-2011 from daily optical imagery acquired from the Moderate Resolution Imaging Spectroradiometer (MODIS). The decreasing trend was tested significant in all seasons, leading to an evident phase drop of the average annual Lake cycle before and after the TGD operation (hereafter referred to as "post-TGD decline"). The most substantial decline appears in fall, which intriguingly coincides with the TGD water storage season. Regional Lake Dynamics exhibits contrasting spatial patterns, with decrease and increase of aggregated Lake area within and beyond the Yangtze floodplain, respectively. Decreasing Lakes in the floodplain, whose elevations are below the natural Yangtze level maxima, pose further puzzling of TGD's impacts on the Lake system. To investigate the underlying mechanism driving the post-TGD Lake decline, a diagnostic approach was proposed based on the conceptual chain where the impact of an inducing factor (e.g., TGD's regulation) usually starts from the Yangtze flows, then propagates to the downstream Yangtze levels, and eventually the surrounding Lake inundation areas. Using in situ measurements and hydrological modeling, daily Yangtze level changes were first quantified along the complete downstream range, as a combined result of i) TGD's flow regulation and ii) Yangtze channel erosion due to reduced sediment load. Derivative impacts on Lake inundation areas were then assessed as empirical functions of Lake-outlet level changes. Results uncover an altered inundation regime of the downstream Lake system by TGD's water regulation, manifested as evident Lake area decrease in fall and increase in spring and winter. As the most substantial influence, reduced Lake area in fall explains ~18-83% of the observed post-TGD decline across the downstream Yangtze Basin. Concurrent Yangtze channel erosion slightly reinforced the area decrease in fall while counteracting ~34% of the area increase in winter. Human water consumption accumulated through the local river network led to constant Yangtze level decrease, which completely counteracted TGD-induced Lake area increase in winter. However, human water consumption only adds minor contribution (l 6%) to the post-TGD Lake decline due to slow increasing rates during 2000-2011. The major proportions of seasonal post-TGD Lake declines were tested to be largely triggered by the decadal climatic drought across the downstream Yangtze Basin; however, the quantified anthropogenic impacts are evident and anticipated to increase in the coming decades due to chronic Yangtze channel erosion and continuous population growth.
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monitoring decadal Lake Dynamics across the yangtze basin downstream of three gorges dam
Remote Sensing of Environment, 2014Co-Authors: Jida Wang, Yongwei Sheng, Tak Shun D TongAbstract:Abstract The Yangtze River Basin downstream of China's Three Gorges Dam (TGD) (thereafter referred to as “downstream” basin) hosts the largest cluster of freshwater Lakes in East Asia. These Lakes are crucial water stocks to local biophysical environments and socioeconomic development. Existing studies document that individual Lakes in this region have recently experienced dramatic changes under the context of enduring meteorological drought, continuous population growth, and extensive water regulation since TGD's initial impoundment (i.e., June, 2003). However, spatial and temporal patterns of Lake Dynamics across the complete downstream Yangtze basin remain poorly characterized. Using daily MODIS imagery and an advanced thematic mapping scheme, this study presents a comprehensive monitoring of area Dynamics in the downstream Lake system at a 10-day temporal resolution during 2000–2011. The studied Lakes constitute ~ 76% (~ 11,400 km2) of the total downstream Lake area, including the entire + 70 major Lakes larger than 20 km2. The results reveal a decadal net decline in Lake inundation area across the downstream Yangtze Basin, with a cumulative decrease of 849 km2 or 7.4% from 2000 to 2011. Despite an excessive precipitation anomaly in the year 2010, the decreasing trend was tested significant in all seasons. The most substantial decrease in the post-TGD period appears in fall (1.1% yr− 1), which intriguingly coincides with the TGD water storage season. Regional Lake Dynamics exhibit contrasting spatial patterns, manifested as evident decrease and increase of aggregated Lake areas respectively within and beyond the Yangtze Plain. This contrast suggests a marked vulnerability of Lakes in the Yangtze Plain, to not only local meteorological variability but also intensified human water regulations from both the upstream Yangtze main stem (e.g., the TGD) and tributaries (e.g., Lakes/reservoirs beyond the Yangtze Plain). The produced Lake mapping result and derived Lake area Dynamics across the downstream Yangtze Basin provides a crucial monitoring basis for continuous investigations of changing mechanisms in the Yangtze Lake system.
