A global lake and reservoir volume analysis using a surface water dataset and satellite altimetry

Lakes and reservoirs are crucial elements of the hydrological and biochemical cycle and are a valuable resource for hydropower, domestic and industrial water use, and irrigation. Although their monitoring is crucial in times of increased pressure on water resources by both climate change and human interventions, publically available datasets of lake and reservoir levels and volumes are scarce. Within this study, a time series of variation in lake and reservoir volume between 1984 and 2015 were analysed for 137 lakes over all continents by combining the JRC Global Surface Water (GSW) dataset and the satellite altimetry database DAHITI. The GSW dataset is a highly accurate surface water dataset at 30&thinsp;m resolution compromising the whole L1T Landsat 5, 7 and 8 archive, which allowed for detailed lake area calculations globally over a very long time period using Google Earth Engine. Therefore, the estimates in water volume fluctuations using the GSW dataset are expected to improve compared to current techniques as they are not constrained by complex and computationally intensive classification procedures. Lake areas and water levels were combined in a regression to derive the hypsometry relationship (dh&thinsp;∕&thinsp;dA) for all lakes. Nearly all lakes showed a linear regression, and 42&thinsp;% of the lakes showed a strong linear relationship with a R2&thinsp;&gt;&thinsp;0.8, an average R2 of 0.91 and a standard deviation of 0.05. For these lakes and for lakes with a nearly constant lake area (coefficient of variation &lt;&thinsp;0.008), volume variations were calculated. Lakes with a poor linear relationship were not considered. Reasons for low R2 values were found to be (1) a nearly constant lake area, (2) winter ice coverage and (3) a predominant lack of data within the GSW dataset for those lakes. Lake volume estimates were validated for 18 lakes in the US, Spain, Australia and Africa using in situ volume time series, and gave an excellent Pearson correlation coefficient of on average 0.97 with a standard deviation of 0.041, and a normalized RMSE of 7.42&thinsp;%. These results show a high potential for measuring lake volume dynamics using a pre-classified GSW dataset, which easily allows the method to be scaled up to an extensive global volumetric dataset. This dataset will not only provide a historical lake and reservoir volume variation record, but will also help to improve our understanding of the behaviour of lakes and reservoirs and their representation in (large-scale) hydrological models.</p

Remotely sensed applications in monitoring the spatio-temporal dynamics of pools and flows along non-perennial rivers: A review

Non-perennial rivers (NPRs) account for more than 50% of the world’s river network and their occurrence is expanding. Some rivers that were previously classified as perennial have evolved to be NPRs in response to climate change and socio-economic uses. There is inadequate understanding of the spatio-temporal dynamics of flows and pools along these rivers due to lack of data, as a priority of river monitoring has been placed on perennial rivers. The current understanding and methods used for monitoring NPRs are mostly derived from perennial rivers perspective. This review paper examines challenges for collecting data on these hydrological attributes of NPRs using current methods. Furthermore, this paper provides an overview of the potential and limitations of using remote sensing data for monitoring NPRs

Understanding the association between climate variability and the Nile's water level fluctuations and water storage changes during 1992–2016

With the construction of the largest dam in Africa, the Grand Ethiopian Renaissance Dam (GERD) along the Blue Nile, the Nile is back in the news. This, combined with Bujagali Dam on the White Nile are expected to bring ramification to the downstream countries. A comprehensive analysis of the Nile's waters (surface, soil moisture and groundwater) is, therefore, essential to inform its management. Owing to its shear size, however, obtaining in-situ data from “boots on the ground” is practically impossible, paving way to the use of satellite remotely sensed and models’ products. The present study employs multi-mission satellites and surface models’ products to provide, for the first time, a comprehensive analysis of the changes in Nile's stored waters’ compartments; surface, soil moisture and groundwater, and their association to climate variability (El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD)) over the period 1992–2016. In this regard, remotely sensed altimetry data from TOPEX/Poseidon (T/P), Jason-1, and Jason-2 satellites along with the Gravity Recovery And Climate Experiment (GRACE) mission, and the Tropical Rainfall Measuring Mission Project (TRMM) rainfall products are applied to analyze the compartmental changes over the Nile River Basin (NRB). This is achieved through the creation of 62 virtual gauge stations distributed throughout the Nile River that generate water levels, which are used to compute surface water storage changes. Using GRACE total water storage (TWS), soil moisture data from multi-models based on the Triple Collocation Analysis (TCA) method, and altimetry derived surface water storage, Nile basin's groundwater variations are estimated. The impacts of climate variability on the compartmental changes are examined using TRMM precipitation and large-scale ocean-atmosphere ENSO and IOD indices. The results indicate a strong correlation between the river level variations and precipitation changes in the central part of the basin (0.77 on average) in comparison to the northern (0.64 on average) and southern parts (0.72 on average). Larger water storages and rainfall variations are observed in the Upper Nile in contrast to the Lower Nile. A negative groundwater trend is also found over the Lower Nile, which could be attributed to a significantly lower amount of rainfall in the last decade and extensive irrigation over the region

Investigation of sediment accumulation in Nubia Lake, using RS/GIS

The main focus of this paper is to detect the changes in AHDL bed surface (sedimentation and erosion) in the period 2000-2012 in the active sedimentation zone of the Lake which is located in Nubia Lake (Sudanese part of AHDL). To enable this detection, the remote sensing (RS) and (Geographic Information Systems) GIS techniques are used to build the 3-D profile of the Lake portion where most of the sediment accumulate. Also, the accumulated sediment during this period is computed using the developed 3-D profile and using the cross section method as conducted by Aswan High Dam Authority (AHDA). Also, the surface areas of sedimentation and erosion are mapped and computed. Results indicated that sedimentation are dominant in years with high flood while erosion occurs when the incoming flow to the lake is low. Moreover, results indicate that the present approach overestimate the sedimentation amount by about 4% compared to the results of the method used by AHDA

Estimativa e avaliação das métricas do reservatório de Serra da Mesa (GO) utilizando a plataforma Google Earth Engine

Esse trabalho objetiva a avaliação da dinâmica temporal do reservatório de Serra da Mesa (GO) de maneira semi-automática e precisa, utilizando imagens orbitais. Para estimar a área plana da barragem foram utilizadas imagens Landsat TM e OLI para o período de 1998 a 2018. As imagens foram processadas por meio da plataforma Google Earth Engine a fim de obter a área da barragem (km²), vazão, dimensão e volume do reservatório ao longo dos anos. A barragem apresentou variação constante de água desde o seu início, com uma tendência decrescente. Os maiores valores das métricas de medição do reservatório foram observados nos anos coincidentes com os maiores volumes da barragem e os menores volumes foram detectados após a implementação de novas barragens a montante. Mais de 90% da variação da dimensão da água pode ser explicada pela área plana da barragem. A plataforma de processamento que utiliza o GEE é eficaz para fornecer uma análise temporal extensa e com grande volume de dados em pouco tempo, com resultados precisos e robustos.The goal of this study was to assess the temporal dynamics of an accumulation reservoir in an accessible and accurate way. The study was conducted on the Serra da Mesa Dam (GO) using orbital images. To estimate the flat area of the dam surface, Landsat TM and OLI images for the period 1998 to 2018 were used. The images were processed using the Google Earth Engine platform (GEE) in order to obtain the dam surface area (km²) and relate it to the flow, altimetric height and volume of the reservoir over the years. The dam showed constant variation of water since its inception, with a decreasing trend. The highest values of the reservoir measurement metrics were observed in the years coincident with the largest areas of the dam, and inversely proportional to the years of the appearance of new dams upstream. More than 90% of the altimetric height variation of water could be explained by the flat area of the dam. The processing platform using the GEE is effective to provide extensive temporal analysis using a large volume of data in a short time, with accurate and robust results

The Economics of Climate Change Adaptation and Water Resources: An Application to Dams

Dam construction has increased rapidly since the 1950’s, especially in developing countries. Climate change is likely to impact the demand for new dams as well as future water and sediment inflow in rivers, thereby influencing the utility, management, and lifetime of dams. Proper construction of dams and sediment management can also help reduce the cost and mitigate the risks dams might be facing as a result of changing climate patterns, which will allow communities to utilize water resources more efficiently and sustainably. This dissertation develops a series of dynamic optimization models to determine how the size of different type of dams and their management strategies can help achieve the above goals. First, a single purpose dam’s optimization problem is explored to arrive at desirable results for maximization of net economics benefits with respect to initial reservoir capacity, sediment removal amount, and decommissioning time. Application of this model to Sambor dam in the lower Mekong River basin shows that allowing for optimal reservoir capacity and sediment removal choice has a significant impact on dam life and total net present value, in the absence of climate change considerations. However, both the desirable reservoir capacity and total net present value vary considerably with climate change. Second, management of multi purpose dams under climate change is discussed with respect to determination of optimal reservoir capacity and sediment removal. These two factors generally increase in magnitude as the functions of a dam and its potential benefits increase. Third, optimal reservoir design and systematic management of cascading dams under climate change are studied for coordinated and non-coordinated cases to arrive at the best policy solution. In the application considered, a coordinated strategy between two dams (Luang Prabang Dam and Xayaburi Dam) is beneficial for the entire system, though the difference between the total net present values from the two types of strategies is relatively small. Generally, coordination resulted in the upstream dam requiring a larger reservoir capacity and accumulating more of incoming sediment in order to ease the negative externality to the downstream dam. Finally, the possibility of dam failure is also incorporated in the model of a single dam based on expected annual peak flood flow trends. An innovation in this regard is the determination of an optimally sized spillway to protect against flood overtopping. Three categories of peak flood flow trends are considered to reflect alternate climate change scenarios. With the risk of dam failure involved, the optimal choice of reservoir capacity and spillway capacity are significantly impacted by water availability and the amount of incoming sediment as influenced by climate factors

Wetland model in an earth systems modeling framework for regional environmental policy analysis

Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division; and (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, June 2011."June 2011." Cataloged from PDF version of thesis.Includes bibliographical references (p. 137-141).The objective of this research is to investigate incorporating a wetland component into a land energy and water fluxes model, the Community Land Model (CLM). CLM is the land fluxes component of the Integrated Global Systems Model (IGSM), a framework that simulates the relationship of physical systems to climate variations. Wetlands play an important role in the storage and regulation of the global water budget so including them in a land water cycle model is found to be necessary in balancing the regional water budgets of simulated river basins. This research focuses on modeling broad hydrological characteristics of wetlands (and lakes) into CLM. CLM's wetland component is reconstructed to reflect a more realistic wetland water budget; it allows for the exchange of water with CLM's river routing component; it allows for varying the storage of wetlands; it allows for calculating discharge from wetlands based on the physics of these ecosystems; and allows the surface water extent of wetlands to vary, a characteristic important to ecological behavior of wetlands and management of wetland ecosystems. The research then implements the modified version of the model for the Sudd wetland, in South Sudan, as it relates to its larger river system, the White Nile. Projects designed to better manage this wetland, such as diverting its inflow to reduce the amount of water consumed by evaporation, are currently under review by its various stakeholders. This diversion stands to change the area of the Sudd, which has direct implications on the ecological and social services derived from the wetland locally. The modified CLM is thus used to provide a better understanding of the science of this management option, and furthers the discussion on the benefits or drawbacks to diversion. Thus, using area as a proxy for environmental impact, what are the environmental, economic and social risks associated with diverting water from inflow into the Sudd? The new wetland component's performance is evaluated against existing observed and modeled data on Sudd hydrology and compared to existing models of the Sudd. The research finds that the potential benefits of diversion cannot be said to unequivocally better the larger system of the White Nile.by Sirein Salah Awadalla.S.M.S.M.in Technology and Polic