Water Surface Area Research Articles

Historical water body changes using spatio temporal indices - a case study of Dakshina Kannada

The spatiotemporal shift of surface water affects the structure, performance, and development of the ecosystem in Dakshina Kannada as well as its agricultural, economic, and social development. In order to better recognize the long-standing variations in the surface water area in Dakshina Kannada, the study used all available Landsat images, the modified Normalized Difference Water Index (MNDWI), the Enhanced Vegetation Index (EVI), and the Normalized Difference Water Index (NDWI) to map the open-surface water from 2014 to 2020 in the Google Earth Engine (GEE) cloud platform. The study looked at precipitation, temperature, and irrigated land to see how weather variation and anthropological actions affect long-standing surface water changes. The following are the outcomes. (1) The Dakshina Kannada, the extreme, periodic, and yearly average water body area values have all decreased during the last 8 years. In the meantime, the number of extreme, periodic, and lasting waterbodies has been steadily increasing. (2) The maximum water body area influences the variance of surface water area in the Dakshina Kannada, whereas the number of minimum water bodies influences the variation of water body number. (3) The area and number of water bodies are statistically significantly improved by rainfall, which also significantly improves water body area and number. The city's water surface area has changed significantly during the last 8 years, according to this study.

Investigations on determination of changes in inactive volume of water reservoirs (case study of South Surkhan water reservoir)

The article develops the change of the reservoir’s useable volume under the effect of turbidity-sediments, considering the turbid discharges' hydrological regime into the reservoir, and proposes a computation technique. Field research was conducted in the South Surkhan reservoir. Based on the data collected from the field research, an electronic map of the reservoir bowl was made, and morphometric indicators were evaluated, considering the formation of muddy sediments in the reservoir. When the standard water level of the water reservoir is 415 meters, the designed water surface area is 65 km2, and the full volume is 800 mln. m3, and according to the results of field research, the full volume of the water reservoir at the level of the normal moisture level is 491.2 mln. m3, the water surface was 72.45 km2. It showed that the full volume of the reservoir was reduced by 38.6 percent compared to the design volume during the operation period, and the water surface area increased by 7.45 km2. The research results allow to determine the change in the useful volume of the reservoir under the influence of turbidity and sediments, to determine the morphometric indicators, and to use the water reserve effectively.

Water Quality Analysis for Agriculture: A Case Study of Nong Khon Saen Community Area, Udon Thani, Thailand

This work aims to assess the water quality in the Nong Khon Saen community area in Udon Thani for agriculture purposes and its suitability for direct use in water consumption. The sample was collected annually from January to March during the period 2019–2022. The work was undertaken to investigate two different water resources (Huai Luang River and Nong Khon Saen reservoir) for the parameters of pH, temperature, electrical conductivity (EC), dissolved oxygen (DO), and biochemical oxygen demand (BOD). The results showed that all parameters of Huai Luang River were within the acceptable limits of Type 3 surface water quality standards from the Pollution Control Department (PCD), Thailand. The average pH was 6.59±0.18 (Std. pH 5–9), temperature was 27±0.01 ℃ (Std. Natural), EC was 679±12.11 μS/cm (Std. None), DO was 5.39±0.63 mg/l (Std. > 4.0 mg/L), and BOD was 1.71±0.70 mg/L (BOD Std. < 2.0 mg/l). The acceptable water quality parameters were caused by general flushing of rainfall, river water flow, and runoff from agricultural fields. Moreover, the water quality of the Nong Khon Saen reservoir showed a higher BOD concentration (2.61±0.54 mg/L) beyond acceptable limits. The high concentration of BOD was caused by the water plants and the decomposition of animals in the surface water area. For other parameters, the average pH (7.11±0.42), Temperature (28±0.01 ℃), EC (689.58±24.18 μS/cm) and DO (8.39±1.13 mg/L) were shown within acceptable limits. Therefore, the water quality is a requirement concerned with agricultural activities that are dependent on water resources.

Research on evaluating the efficiency of recovery nutrients (N, P) in an integrated ecology system for catfish farming

The purpose of this is to evaluate the ability to recover nutrients (N, P) emitted from catfish farming by using an integrated ecological system towards zero emissions. An integrated system has been designed and implemented for a catfish pond with a water surface area of 10,300 m2. Wastewater is treated with water hyacinth, sludge is used for organic fertilizer production, and dead fish carcasses are used as raw material for liquid fertilizer production. The SFA (substance flow analysis) method was applied to evaluate the efficiency of nutrient source recovery in the system. The results show that the nutrient supply to fish ponds is mainly from fish food (about 30,450 kgN/ha/crop and 3,675 kgP/ha/crop). Harvested fish in the adult stage accumulate N and P content in fish biomass of 12,480 kgN ha/crop and 540 kgP/ha/crop respectively. Wastewater from fish ponds sent through aquatic ditches has an amount of 11,509 kgN/ha/crop and 2,978 kgP/ha/crop. The treatment efficiency of the aquatic pond reached 70%, and the amount of nutrients emitted into the environment through wastewater was 3,453 kgN/ha/crop and 893 kgP/ha/crop respectively. The efficiency of retaining nutrients after composting is about 70 - 80%, the product of this process is organic fertilizer containing N and P contents of 0.26% and 0.12% respectively.

Evolutions of water surface area and evaporation loss of Three Gorges Reservoir based on Landsat images, 1982-2021

Evolutions of water surface area and evaporation loss of Three Gorges Reservoir based on Landsat images, 1982-2021

Применение спектральных водных индексов на хвостовом хозяйстве Дарасунского рудника по данным дистанционного зондирования Земли программы Landsat

At present, the problem of ensuring the environmental safety of tailings dumps and dams holding them is acute in the mining cluster not only in Russia, but also in the world. Stale tailings located in a hydraulic structure are man-made deposits and are considered as an object of development in the future. Therefore, the formation of a database of the areas of the water mirror of the basins of the cascade of tailings for a long period of operation is an urgent scientific problem. It is important to analyze and predict potential threats to the city-forming mining enterprise and nearby territories. This problem can be solved by using geoinformation systems and multispectral data. The object of the research is a complex of tailings dumps’ cascades of the Darasunsky mine. The goal is to provide spatio-temporal assessment of the areas of the water mirror of the basins of the tailings dumps’ cascade of the Darasunsky mine for the period from 1997 to 2022 in order to predict environmental safety. The research objectives are the following: assessment of the environmental situation at the Darasunsky mine; selection of the optimal method for decoding the water surface; collection and formation of an archive of remote sensing data; calculation of spectral indices and retrospective analysis of changes in the water surface area of the tailings of the Darasunsky mine; forecast of emergency situations of lithospheric, hydrospheric, airborne, biological pollution. A spatio-temporal assessment of the areas of the water mirror of the basins of the tailing dumps’ cascade has been made to assess the use intensity of these structures with the construction of graphs of changes in the areas of the water surface over a 25-year period. Thanks to the division of the tailings storage into cascades, it has become possible to locally determine the filling of 4 tailings sections with tailings pulp. The data obtained allow monitoring for the rational use, conservation, stopping the operation of hydraulic structures (in particular tailings dumps), their impact on the environment. The use of spectral water indices according to the remote sensing data of the Landsat program will allow predicting and preventing emergency situations at the tailings dump, which has been in operation for many decades, to prevent the overflow of water over the crest and body of the enclosing dams.

Impacts of the Major Drought in Chile and Mitigation Measures

Since 2010, Chile has experienced a megadrought. It is the most persistent and severe climatic issue of the last millennium, affecting not only precipitation and temperature but also lakes and glaciers. This article aims to summarize the specific impacts caused by the drought in Chile and give some advice to alleviate these effects. To begin with, the study will focus on analyzing the increase in temperature, decrease in rainfall, and decline in water surface area of particular lakes. Additionally, it will delve into the effects of climate change on plant and animal species as well as human activities, including a decrease in vegetation coverage, disruption of the food chain, a substantial reduction in biodiversity, and a decline in gross domestic product (GDP). Finally, the study will also propose a range of measures to minimize these impacts from both biological and political perspectives. There are two main ways: (i) change the genes of plants to make them more adaptable to the environment; (ii) transport sea water from the Pacific Ocean and build water management plants. In the future, scientists and governments will be required to find more ways to mitigate the impacts of the megadrought and promote some measures to protect the environment. This article could provide some new ideas for improving the climate in Chile in the future.

Учет затенения при моделировании эффективной поверхности рассеяния морской поверхности

The effectiveness of the implementation of radar systems for water areas monitoring is inextricably linked with the creation of adequate models of the radar cross-section (RCS) of the sea surface, which are required for the efficient detection and tracking of surface objects in order to ensure the safety of marine navigation. The article considers the influence of shading of waves that are far from the observer by closer ones. The modeling of the sea surface based on the Longuet-Higgins probability model for various sea surface conditions ranging from moderate to strong is considered and corresponding simulations are performed. For the obtained models, statistical analysis of the visibility of water surface areas was carried out. It is shown that within the applied wave model, the shading effect appears the most pronounced when the direction of observation is collinear with the wind direction, and the least pronounced at the perpendicular direction. It has been established that with strong waves, the effect of shading is more pronounced. Based on the results of the analysis, an approach to take into account the shading effect in modeling the RCS of the sea surface was proposed.

Basin‐Scale CO2 Emissions From the East River in South China: Importance of Small Rivers, Human Impacts and Monsoons

AbstractRiverine carbon dioxide (CO2) emissions are an essential component of the riverine carbon cycle, but an accurate assessment of riverine CO2 emission fluxes is still hindered by the spatial and temporal variations among river basins caused by differences in climate, watershed characteristics, and human activity. Here, we evaluate the riverine CO2 flux from the subtropical East River Basin (ERB) in south China, a region strongly affected by monsoon climate and anthropogenic land use changes. Our results suggest small rivers are major contributors to riverine CO2 emissions, even with relatively low CO2 concentrations and small water surface areas (SAs). They contribute disproportionately to 74.4% of the total fluxes due to high gas transfer velocity (k) across the water‐air interface. Land use changes have substantially enhanced CO2 emissions from river networks. Normalized areal riverine CO2 fluxes in the urban‐ and cropland‐dominated Middle and Lower ERB (27.6 and 39.4 g C m−2 yr−1) were two and three times higher than the 9.1 g C m−2 yr−1 in the forest‐dominated Upper ERB. Due to the larger water SA and higher k caused by monsoon‐induced precipitation, the East River acts as a stronger carbon source during the wet season, emitting 0.67 Tg C yr−1 to the atmosphere, which is about twice that during the dry season (0.33 Tg C yr−1). Our study illustrated how monsoon climate and land use in the ERB have regulated its riverine CO2 emissions. Our findings also provided valuable insights into the role of small rivers in the basin‐wide carbon cycle.

Геоэкологическая характеристика водного объекта без названия, расположенного вблизи рекультивированного полигона твердых коммунальных отходов Калининградской области

The article presents the results of a study of one of the artificial reservoirs in Kaliningrad – a pond w / n with coordinates 54°69ʹ90ʺ N, 20°36ʹ46ʺ E. (hereinafter – the pond), located 0,4 km south of the reclaimed municipal solid waste landfill (hereinafter – the MSW landfill) in the settlement named after A. Kosmodemyansky (Kaliningrad) and 0,6 km from the water area of the Vistula Bay, which is a reservoir of the highest category, which is both amateur and industrial fishing. Through the pond, since the formation of the MSW landfill in 1978, there has been a surface runoff of water containing leachate from the waste dump. After landfill reclamation, the pond is studied for the state of its biota, the chemical composition of water and bottom sediments. The objectives of this study include assessing the degree of impact on the aquatic ecosystems of the MSW landfill by studying the relief features of the pond basin, determining and comprehensively analyzing the obtained morphometric indicators that have a significant impact on the appearance and development of the reservoir, its hydrological regime, the distribution of physicochemical parameters in the thickness water and the current ecological state. In 2021, a bathymetric survey was carried out using a Lowrance HDS-16 echo sounder-chartplotter, during which information about the current depth and geographic coordinates of the studied bottom area was jointly recorded in real time. For the first time, maps of the relief of the bottom of the pond in 2D and 3D format were built. Investigated the drainage basin of the pond. During the subsequent analysis of the obtained results, the main morphometric parameters of the pond were determined. According to the results of calculations, the pond can be attributed to shallow ponds of medium size, with a water surface area of 0,035 km2 and an average depth of 1.8 m. The outlines of its coastline are close to a square.

ОЦІНКА ЗАРЕГУЛЬОВАНОСТІ СТОКУ РІЧКИ СЕРЕТ

The Seret River is a 242 km long left tributary of the Dniester, flowing within the Ternopil region. The basin covers an area of 3900 km2, a river slope of 0,9 and a river network density of 2,44 km2/km. The average long-term water discharge in the river is 12,1 m3/s, the water turbidity is 100-200 g/m3 and the salinity is 350-550 mg/dm3. There are 8 small hydropower plants on the river with a total capacity of 21,57 MW. The aim of the study is to assess the regulated flow of the Seret River and determine the amount of siltation in the reservoirs in its channel. The study found that 8 reservoirs have been created on the Seret River, with a total water surface area of 21 km2 and a total volume of 57,4 million m3. The Seret River is one of the most heavily regulated rivers in the Western Podillia. The Seret River basin contains 30% of all reservoirs in the Ternopil region. The upper reaches of the river are the most regulated, with 5 reservoirs with a total volume of about 33 million m3 and a usable volume of 25 million m3. According to the results of the calculations, it was found that the coefficient of flow regulation of the Seret River is 0,17; the degree of flow regulation is 0,25. The volume weight of sediment in the Seret River is 0,79 t/m3. It was found that the river transports about 57 thousand tonnes of sediment per year. Over the estimated period of operation (40 years), 3 million m3 of sediment will accumulate in the Seret River reservoirs. The siltation of Ternopil reservoir is 3,5 %, Vertelivske – 5 %, Zalozhtsivske – 10 %, Verkhnya Ivachyvka – 58 %, Bilche-Zolotetske – 65 %, Skorodynske – 75 %. Based on the results obtained, it can be concluded that the Seret River is undergoing significant anthropogenic pressure, and there are risks of degradation of the watercourse and a decrease in the energy potential of the reservoirs in the middle and lower reaches of the river. Therefore, there is a need to develop scientifically based measures to optimise nature management and renaturalise the Seret River basin and valley.

Real-time and dynamic estimation of CO<sub>2</sub> emissions from China��s lakes and reservoirs

<p>Lakes and reservoirs act as active carbon (C) reactors and regulators. Both play a crucial terrestrial ecosystem C balance role via carbon dioxide (CO<sub>2</sub>) exchange processes across the water-air interface. It has previously been confirmed that CO<sub>2</sub> flux from lakes and reservoirs generally exhibits significant spatiotemporal heterogeneity. Nevertheless, spatiotemporal CO<sub>2</sub> flux variation has seldom been considered in global and regional CO<sub>2</sub> emission estimates from lakes and reservoirs. By accounting for spatiotemporal CO<sub>2</sub> flux and water surface area variability, we evaluated spatial and temporal CO<sub>2</sub> emission dynamics from China��s inland lakes and reservoirs using national real-time water quality monitoring data and machine learning (ML) models. Between 2021�C2022, we estimated total C emission flux at 6.78 (��2.5) Tg C yr<sup>?1</sup>, where seasonal and regional distribution both exhibited significant heterogeneity. Our state-of-the-art estimate is significantly lower than previous estimates of 7.9~25 Tg C yr<sup>?1</sup> from the 1980s to the 2010s. Water quality parameters (pH and dissolved oxygen [DO]) and climate factors (air temperature) were identified as the general environmental CO<sub>2</sub> flux controls. For the first time, this study clarifies the spatiotemporal patterns and drivers of CO<sub>2</sub> flux from China��s inland lakes and reservoirs, providing a more complete C budget picture of China��s aquatic ecosystems.</p>

SWRNet: A Deep Learning Approach for Small Surface Water Area Recognition Onboard Satellite

SWRNet: A Deep Learning Approach for Small Surface Water Area Recognition Onboard Satellite

Temporal and Spatial Evolution of Eichmann Lake Wetland in Aksu River Basin and Its Response to Ecological Water Supply.

Timely understanding and quantitative analysis of the changing trend in natural ecosystems in arid and semi-arid areas and their response to the ecological water supply process are of great significance for maintaining the health of oasis ecosystems. Taking the Eichmann Lake wetland of the Aksu River Basin in Xinjiang as the research area, the temporal-spatial distribution characteristics of the lake and the response of ecological water in recent years were studied based on remote sensing images and monitoring data. The results show that: (1) The water surface area of Eichmann Lake is shrinking, from 61.57 km2 in 1996 to 27.76 km2 in 2020. The changes in water surface area have experienced three stages: rapid decline, slow decline, and slow recovery. After the ecological water supply, the water surface area has obvious seasonal changes with hysteresis; (2) In areas with a low average water level, the ecological water supply has a significant impact on the groundwater level. The higher the water supply is, the higher the groundwater level will be. There is a significant lag effect between the change in the groundwater level and the response of the ecological water supply, which is 1-2 months; (3) The response characteristics of different natural vegetation to the ecological water supply were different in interannual, seasonal, and spatial contexts. The response of Populus euphratica to the ecological water supply is obvious, and its growth is the best within the range of 100-500 m from the water supply outlet. This research can provide the basis for the rational allocation of the Aksu River Basin's water resources, and also act as a valuable reference for the restoration and reconstruction of surrounding vegetation in the Aksu River irrigation area.

High-resolution water level and storage variation datasets for 338 reservoirs in China during 2010–2021

Abstract. Reservoirs and dams are essential infrastructure in water management; thus, information of their surface water area (SWA), water surface elevation (WSE), and reservoir water storage change (RWSC) is crucial for understanding their properties and interactions in hydrological and biogeochemical cycles. However, knowledge of these reservoir characteristics is scarce or inconsistent at the national scale. Here, we introduce comprehensive reservoir datasets of 338 reservoirs in China, with a total of 470.6 km3 storage capacity (50 % Chinese reservoir storage capacity). Given the scarcity of publicly available gauged observations and operational applications of satellites for hydrological cycles, we utilize multiple satellite altimetry missions (SARAL/AltiKa, Sentinel-3A and Sentinel-3B, CroySat-2, Jason-3, and ICESat-2) and imagery data from Landsat and Sentinel-2 to produce a comprehensive reservoir dataset on the WSE, SWA, and RWSC during 2010–2021. Validation against gauged measurements of 93 reservoirs demonstrates the relatively high accuracy and reliability of our remotely sensed datasets. (1) Across gauge comparisons of RWSC, the median statistics of the Pearson correlation coefficient (CC), normalized root mean square error (NRMSE), and root mean square error (RMSE) are 0.89, 11 %, and 0.021 km3, with a total of 91 % validated reservoirs (83 of 91) having good RMSE from 0.002 to 0.31 km3 and NRMSE values smaller than 20 %. (2) Comparisons of WSE retracked by six satellite altimeters and gauges show good agreement. Specifically, the percentages of reservoirs having good and moderate RMSE values smaller than 1.0 m for CryoSat-2 (validated in 30 reservoirs), SARAL/AltiKa (9), Sentinel-3A (34), Sentinel-3B (25), Jason-3 (11), and ICESat-2 (26) are 77 %, 75 %, 79 %, 87 %, 81 %, and 82 %, respectively. By taking advantages of six satellite altimeters, we are able to densify WSE observations across spatiotemporal scales. Statistically, around 96 % of validated reservoirs (71 of 74) have RMSE values below 1.0 m, while 57 % of reservoirs (42 of 74) have good data quality with RMSE values below 0.6 m. Overall, our study fills such a data gap with regard to comprehensive reservoir information in China and provides strong support for many aspects such as hydrological processes, water resources, and other studies. The dataset is publicly available on Zenodo at https://doi.org/10.5281/zenodo.7251283 (Shen et al., 2021).

Multiwater Index Synergistic Monitoring of Typical Wetland Water Bodies in the Arid Regions of West-Central Ningxia over 30 Years

The Shapotou National Nature Reserve in the Ningxia Hui Autonomous Region is a typical arid region in China. There is an exceptionally serious problem of surface water resource conservation, and dynamic monitoring of surface water with the help of water indices can help to elucidate its change patterns and impact mechanisms. Here, we analysed the characteristics of interannual variation in surface water area in the study area from 1992–2021. The correlation coefficients of the surface water area in the previous year and the contemporaneous water bodies of the Yellow River with the total surface water area (TSWA) were calculated. The results show the following: ① In terms of the classification accuracy of the two methods, water indices and support vector machine classification, water indices are more suitable for water body extraction in the study area. In particular, the three water indices, NDWI, MNDWI and AWEIsh, were more effective, with average overall accuracies of 90.38%, 90.33% and 90.36% over the 30-year period, respectively. ② From the TSWA extraction results from the last 30 years, the TSWA showed an increasing trend with an increase of 368.28 hm2. Among the areas, Tenggeli Lake contributed the most to the increase in TSWA. ③ The highest correlation between the TSWA and the previous year’s TSWA was 0.89, indicating that the better way to protect the water body is to maintain water surface stability year-round. The surface water area of the Yellow River and TSWA also showed a strong correlation, indicating that the rational use of Yellow River water is also an important direction for the future conservation of water resources in the study area.

Analysis of Surface Area Fluctuation of the Haramaya Lake using Remotely Sensed Satellite Imagery

Human’s unwise and ineffective exploitation behavior has caused losses of the vital natural resources, soil and water, which will definitely leave the future of the next generation in jeopardy. As a result of human intervention and natural causes most lakes in Ethiopia are shrinking in size while others are showing increase in volume. The intensive exploitation, beyond its regeneration rate, of the Lake Haramaya for water supply and agricultural purposes by the community within and outside its catchment boundary has led to its extinction. Although, some studies have been conducted on land use/land cover dynamics, the focus given to quantification of temporal variability lake surface area and the impact of weather variability on the lake water was inadequate. Hence, this study was conducted with the prime objective of mapping/quantifying the temporal lake surface area fluctuation using time series remote sensing images and investigating the impact of weather/climate variability on the lake. After acquiring Landsat images of the years 1985, 1995, 2003, 2010 and 2016 over the dry Haramaya Lake basin (path/row 166/54), the Modified Normalized Difference Water Index (MNDWI) and the Normalized Difference Vegetation Index (NDVI) were used for enhancing and extracting the open water surface of the lake. All of the enhanced images display a trend of decreasing lake surface water area with an average shrinkage of 23.6% between the year 1985 and up to its disappearance. After 2000 the lake surface area shrinkage was at its maximum which has a direct relation with the occurrence of dry weather as a result ofrelatively higher temperature and low rainfall between the years 2000 to 2003.

Surface water and aerosol spatiotemporal dynamics and influence mechanisms over drylands

Under the background of global warming and excessive human activities, much surface water in drylands is experiencing rapid degradation or shrinkage in recent years. The shrinkage of surface water, especially the degradation of lakes and their adjacent wetlands in drylands, may lead to the emergence of new salt dust storm hotspots, which causes greater danger. In this paper, based on high spatial resolution global surface water (GSW) and multiangle implementation of atmospheric correction (MAIAC) AOD data, we systematically analyze the dynamic characteristics of surface water and aerosols in typical drylands (Central Asia, CA) between 2000 and 2018. Simultaneously, combined with auxiliary environment variables, we explore the driving mechanisms of surface water on the regional salt/sand aerosols on different spatial scales. The results show that the seasonal surface water features an increasing trend, especially a more dramatic increase after 2015, and the permanent surface water indicates an overall decrease, with nearly 54.367 % at risk of receding and drying up. In typical lakes (Aral Sea and Ebinur Lake), the interannual change feature of the surface water area (WA) is that a continuous decrease during the study period occurs in Aral Sea area, yet a significant improvement has occurred in Ebinur Lake after 2015, and the degradation of Ebinur Lake takes place later and its recovery earlier than Aral Sea. The aerosol optical depth (AOD) in CA shows obvious seasonal variation, with the largest in spring (0.192 ± 0173), next in summer (0.169 ± 0.106), and the smallest in autumn (0.123 ± 0.065). The interannual variation of AOD exhibits an increase from 2000 to 2018 in CA, with high AOD areas mainly concentrated in the Taklamakan Desert and some lake beds resulting from lake degradation, including Aral Sea and Ebinur Lake. The AOD holds a similar trend between Aral Sea and Ebinur Lake on an interannual scale. And the AOD over Ebinur Lake is lower than that over Aral Sea in magnitude and lags behind in reaching the peak compared with Aral Sea. The WA change can significantly affect aerosol variation directly or indirectly on the aerosol load or mode size, but there are obvious differences in the driving mechanisms, acting paths, and influence magnitude of WA on aerosols on different spatial scales. In addition, the increase of WA can significantly directly suppress the increase of Ångström exponent (AE), and the effects of WA on AOD are realized majorly by an indirect approach. From the typical lake perspective, the effects of WA on aerosol in Aral Sea are achieved via an indirect path; and the decrease of WA can indirectly promote the AOD rise, and directly stimulate the AE growth in Ebinur Lake.

Quantifying surface water decreasing in Segara Anakan Lagoon

Segara Anakan is the largest mangrove-fringed lagoon on the south coast of Java Island. It is a productive coastal system that provides environmental services for the community in the vicinity of the lagoon, such as fisheries production and tourism. Right now, the lagoon is facing surface water shrinking due to the intensive sedimentation process. The fishing ground area becomes limited; thus, the fisherman should sail further to the sea zone to catch fish. To quantify the lagoon’s surface water decreasing rate, we applied a spatial analysis method. Historical cartographic maps and satellite images of Segara Anakan were digitised using ArcMap. We used a reclassification tool to classify land and water for the satellite image before digitising it. The result showed that the lagoon’s surface water area decreased from 65 km2 in 1942 to 8.5 km2 in 2017. Since the lagoon received freshwater supply from Citanduy River, we applied Universal Soil Loss Equation (USLE) to calculate sediment supply from the watershed. The result showed that from 2005 to 2016, the average sediment supply reached 3 mm/year or equal to 22 million tons/year. The highest sediment supply rate occurred in 2010 at 5.14 mm/year or similar to 43 million tons/year. Linking between integrated coastal zone management with watershed management should be implemented to reduce the rate of sedimentation.

Naive Bayes classification-based surface water gap-filling from partially contaminated optical remote sensing image

Optical remote sensing images are a common data sources for surface water monitoring, while they are easily contaminated by clouds, cloud shadows, terrain shadows, etc., resulting in spatial gaps in surface water images. This paper proposes a surface water gap-filling method based on Naive Bayes classification. It uses the historical cloud-free binary (water, non-water) surface water images as prior data and the uncontaminated pixels in the partially contaminated ternary (water, non-water, contaminated pixels) surface water image as evidence to identify the category of gap pixels to achieve the purpose of gap-filling. This method considers the relationship between disconnected water bodies and does not depend on terrain data. When the image is heavily covered by clouds, this method can also reconstruct the complete water extent accurately. Five study areas with different scenarios including rivers, lakes or reservoirs, are selected to evaluate the method. Results show that the average gap-filling accuracy in all five study areas is over 90 %. After gap-filling, the time series of surface water area presents a good correlation with the time series of water level (e.g., the coefficient of determinationR2 = 0.95 in the Dartmouth reservoir). The proposed method is proved effective in filling gaps caused by clouds, cloud shadows and terrain shadows in surface water image, and it would be suitable for high-frequency surface water monitoring and near real-time surface water mapping.