Browsing by Author "Ali, Syed Azhar"

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    Assessment and validation of total water storage in the Chesapeake Bay watershed using GRACE
    Sridhar, Venkataramana; Ali, Syed Azhar; Lakshmi, Venkataraman (Elsevier, 2019-05-22)
    The Chesapeake Bay is the largest estuary in the United States, and its catchment has heterogeneous hydrological and geomorphologic characteristics. It includes seven major river basins: James, Patuxent, Potomac, Rappahannock, Susquehanna, Western Shore, Eastern Shore, and York. Remote sensing data, along with in-situ observations of streamflow and simulated water budget components, can provide significant understanding of variability in water resources availability in this diverse watershed. In this study, we quantify the terrestrial water storage using both remote sensing and in-situ data and hydrologic model outputs in the Chesapeake Bay watershed. Total water storage change (TWSC) was calculated based on the combination of three methods to identify the best approach in estimating TWSC. These methods evaluated different sources of data, including Parameter elevation Regression on Independent Slopes Model (PRISM) precipitation, MODIS ET, U.S. Geological Survey observed streamflow, and the Variable Infiltration Capacity (VIC) model. Estimated TWSC were in close agreement with GRACE-derived TWSC when we employed VIC-simulated streamflow after calibration with observed streamflow. However, the use of VIC-simulated ET or MODIS-derived ET yielded similar results for TWSC. Assessment of TWSC during extreme events (drought) during the summer months revealed that predicting ET is critical for TWSC in June–August and that VIC-simulated TWSC could be a reliable proxy for GRACE data to assess the water availability in the watershed.
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    Deriving the Reservoir Conditions for Better Water Resource Management Using Satellite-Based Earth Observations in the Lower Mekong River Basin
    Ali, Syed Azhar; Sridhar, Venkataramana (MDPI, 2019-12-03)
    The Mekong River basin supported a large population and ecosystem with abundant water and nutrient supply. However, the impoundments in the river can substantially alter the flow downstream and its timing. Using limited observations, this study demonstrated an approach to derive dam characteristics, including storage and flow rate, from remote-sensing-based data. Global Reservoir and Lake Monitor (GRLM), River-Lake Hydrology (RLH), and ICESat-GLAS, which generated altimetry from Jason series and inundation areas from Landsat 8, were used to estimate the reservoir surface area and change in storage over time. The inflow simulated by the variable infiltration capacity (VIC) model from 2008 to 2016 and the reservoir storage change were used in the mass balance equation to calculate outflows for three dams in the basin. Estimated reservoir total storage closely resembled the observed data, with a Nash-Sutcliffe efficiency and coefficient of determination more than 0.90 and 0.95, respectively. An average decrease of 55% in outflows was estimated during the wet season and an increase of up to 94% in the dry season for the Lam Pao. The estimated decrease in outflows during the wet season was 70% and 60% for Sirindhorn and Ubol Ratana, respectively, along with a 36% increase in the dry season for Sirindhorn. Basin-wide demand for evapotranspiration, about 935 mm, implicitly matched with the annual water diversion from 1000 to 2300 million m3. From the storage–discharge rating curves, minimum storage was also evident in the monsoon season (June–July), and it reached the highest in November. This study demonstrated the utility of remote sensing products to assess the impacts of dams on flows in the Mekong River basin.
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    Human-Induced Alterations to Land Use and Climate and Their Responses for Hydrology and Water Management in the Mekong River Basin
    Sridhar, Venkataramana; Kang, Hyunwoo; Ali, Syed Azhar (MDPI, 2019-06-25)
    The Mekong River Basin (MRB) is one of the significant river basins in the world. For political and economic reasons, it has remained mostly in its natural condition. However, with population increases and rapid industrial growth in the Mekong region, the river has recently become a hotbed of hydropower development projects. This study evaluated these changing hydrological conditions, primarily driven by climate as well as land use and land cover change between 1992 and 2015 and into the future. A 3% increase in croplands and a 1–2% decrease in grasslands, shrublands, and forests was evident in the basin. Similarly, an increase in temperature of 1–6 °C and in precipitation of 15% was projected for 2015–2099. These natural and climate-induced changes were incorporated into two hydrological models to evaluate impacts on water budget components, particularly streamflow. Wet season flows increased by up to 10%; no significant change in dry season flows under natural conditions was evident. Anomaly in streamflows due to climate change was present in the Chiang Saen and Luang Prabang, and the remaining flow stations showed up to a 5% increase. A coefficient of variation <1 suggested no major difference in flows between the pre- and post-development of hydropower projects. The results suggested an increasing trend in streamflow without the effect of dams, while the inclusion of a few major dams resulted in decreased river streamflow of 6% to 15% possibly due to irrigation diversions and climate change. However, these estimates fall within the range of uncertainties in natural climate variability and hydrological parameter estimations. This study offers insights into the relationship between biophysical and anthropogenic factors and highlights that management of the Mekong River is critical to optimally manage increased wet season flows and decreased dry season flows and handle irrigation diversions to meet the demand for food and energy production.
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    Sustainable Management of Water Resources and Hydropower Projects in the Context of the Food-Energy-Water Nexus in the Mekong River Basin
    Ali, Syed Azhar (Virginia Tech, 2020-11-16)
    The Mekong River Basin (MRB) is one of the largest transboundary basins in the world shared between six south Asian countries. The Mekong river supports a population of more than sixty million people through irrigation and fisheries for their survival and hosts approximately 88,000 MW of unharnessed hydropower potential. The construction of the dams for the supply of energy has a wide-ranging effect on the downstream regions of reservoirs, causing unprecedented and devastating damage to the environment and livelihood of people. The dissertation examines the optimal operation of the dams for the equitable distribution of water between irrigation, domestic, and hydropower sectors with minimal effect on the downstream ecosystem by estimating the cascading effects of dams in the MRB. The hydrological characteristic of the MRB was simulated using the high resolution (1 km) Variable Infiltration Capacity (VIC) hydrological model with the Lohmann et al. (1996, 1998) routing scheme and general circulation models projection for the future till 2099. Remote sensing products were used for the derivation of the reservoir behaviors, while the net irrigation water requirement (NIWR) was simulated by the irrigation scheme embedded in the improved VIC model. The VIC-MODFLOW (VIC-MF) coupled model was used for the investigation of the interaction between the surface and groundwater movement. The hydropower potential of the dams was estimated using the modified Hanasaki et al. (2006) approach by explicitly considering the irrigation water demand from the expanding and intensifying agricultural activities. A system dynamic model for the MRB was developed for the sustainable optimization of water allocation to meet the needs from the irrigation, domestic, hydropower generation, and ecological sectors. Economic analysis was performed to evaluate the existing and future conditions over the resource surplus regions with consideration of social impacts. Streamflows in the MRB varied substantially with the peak monthly streamflow from 10 m3/sec to 40,000 m3/sec. The inflows to dams in both main river and tributaries are projected to increase from 1.2% to 25% under RCP 4.5 and a decrease of 28.5% - 74.7% under RCP 8.5 during 2020-2099 as compared to the historic mean. The NIWR for the MRB was calculated as 65,000 million m3 for the observed period (1981-2019) with a decrease of 0.25% for the future period. The groundwater interaction is expected to enhance the surface streamflow resulting in additional inflow to dams. The multipurpose reservoirs were able to generate the desired annual energy ranging from 15 GWh to 400 GWh along with satisfying more than 80% of the irrigation water demand. Similarly, the irrigation reservoirs also satisfied more than 80% of the water demand for irrigation and hydropower reservoirs to generate the required energy between 2 GWh and 18990 GWh. Climate change will enhance the hydropower potential with an average increase of 7.3% and 5.3% in the future under RCP 4.5 and RCP 8.5, respectively. The increase in the irrigated area (5% and 10%) reduces the energy generation of the multipurpose dams by 1.5%, however, the addition of a crop cycle lowers the energy generation by more than 10%. The system dynamics model showed the multipurpose dams produced annual energy of 316 GWh and satisfied more than 60% of the irrigation, municipal, and industrial sectors water demand during 2006-2019. Similarly, irrigation dams supplying more than 60% of the irrigation water demand, and 50% of the municipal and industrial sectors demand. Climate change has a positive influence on the performance of the dams. The assessment of the shadow price shows that the dam operation in Thailand, Laos PDR, and China will be sufficient to meet the water demands of the energy, irrigation, municipal, and industrial sectors, while the energy sector of Cambodia and Vietnam may experience adverse impacts.
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    Systems Analysis of Coupled Natural and Human Processes in the Mekong River Basin
    Sridhar, Venkataramana; Ali, Syed Azhar; Sample, David J. (MDPI, 2021-09-12)
    The Mekong River Basin is one of the world’s major transboundary basins. The hydrology, agriculture, ecology, and other watershed functions are constantly changing as a result of a variety of human activities carried out inside and by neighboring countries including China, Myanmar, Thailand, Laos, Cambodia, and Vietnam in order to meet increased food and water demands for an increasing population. The Mekong River, which provides irrigation and fishing for a population of over 60 million people, also has an estimated 88,000 MW of untapped hydropower potential. The construction of dams for energy supply has a wide-ranging impact on downstream reservoir regions, resulting in unprecedented changes in hydrologic functions, the environment, and people’s livelihoods. We present a holistic view of how external stressors such as climate change and variability, land cover, and land-use change affect supply and demand. We present an integrated modeling framework for analyzing the supply–demand scenarios and tradeoffs between different sectors. Specifically, we evaluated the impacts of future climate on irrigation, hydropower, and other needs in the basin through a feedback loop. We focused on hydrologic extremes to evaluate their impacts on the reservoir operations during flood and low flow events. The inflow is projected to change by +13% to −50% in the future, while a 0.25% (15.24 billion m3) reduction is projected for the net irrigation water requirement (NIWR). A unit percentage increase in irrigation demand will reduce energy generation by 0.15%, but climate change has a beneficial impact on dam performance with a predicted increase in energy generation and supply to all sectors. Flood events will cause excessive stress on reservoir operation to handle up to six times more flow volumes; however, the low-flow events will marginally affect the system. While the flow and storage rule curves consider both supply and demand, changing human water use comes second to changing climate or other biophysical considerations. This paper emphasizes the importance of considering feedback between climate–water–human society in the systems modeling framework in order to meet societal and ecological challenges. The findings will provide information on the risks and tradeoffs that exist in the water, energy, and food sectors of the basin.