Entire River Basin Research Articles

Predicting hydrologic flows under climate change: The Tâmega Basin as an analog for the Mediterranean region

The potential effects of climate change on the hydrology of the Tâmega River basin, northern Portugal, are assessed by comparing simulated hydrologic scenarios derived from both observational climate databases for a recent past period (1950–2015) and EURO-CORDEX model simulations for the future (2021−2100). Future climate change scenarios are based on an ensemble of five climate model chain experiments and on two Representative Concentration Pathways (RCP4.5 and RCP8.5). Basin-mean annual temperatures are ca. 10% or 20% warmer than in recent past climate (12.4 °C) for RCP4.5 and RCP8.5, respectively. Furthermore, basin-mean annual precipitation decreases by approximately 8% or 13%, when compared to recent past (1255 mm). The Hydrological Simulation Program FORTRAN (HSPF) is applied to the historical data and to each of the five model simulations separately so as to simulate potential changes in flowrates. The model is calibrated and validated using 5 hydrometric stations, achieving satisfactory results regarding flowrate simulation. A reconstruction of flowrates within the entire river basin and over the historical period is accomplished, which is particularly useful when observed data is missing. The projected climate change impacts on annual flowrates reveal a decrease from 18% to 28% relative to observations (70.9 m3 s−1). These findings provide valuable information for the future management and planning of water resources (water security) and can be largely generalized not only to other basins in Portugal, but also over most of Southern Europe and throughout the Mediterranean Basin, where significant warming and drying trends are widespread footprints of climate change.

Quantitative analysis of the drainage and morphometric characteristics of the Palar River basin, Southern Peninsular India; using bAd calculator (bearing azimuth and drainage) and GIS

ABSTRACTThe Palar River basin is one of the major rivers in southern peninsular India. Morphometric analysis coupled with drainage network analysis was carried out for the Palar River basin to understand its drainage characteristics and the drainage network geometry with reference to tectonics. The morphometric analysis has been carried out using ‘bearing azimuth and drainage (bAd) calculator’ which a new and easy methodology for extraction of watershed morphometric parameters. The entire Palar River basin has been divided into five major sub-basins and various linear, areal, and relief morphometric parameters were calculated. The sub-basins I, II, and III reflect low to medium stream frequency (Fs) and moderate drainage density (Dd) and a high bifurcation ratio of various stream orders signifies that they are surging through tectonically active areas, followed by high overland flow and less recharge into the subsurface resulting in low groundwater potential. Moreover, sub-basins IV and V show the relatively low overland flow, which helps to percolate water, hence ground water potential will be higher. The morphometric result suggests that the drainage network geometry is variously controlled by recent tectonics. Lineaments trending majorly NW-SE, NE-SW, and E-W mark the major drainage network in Palar River drainage basin. Lower order streams and higher order streams follow NW-SE, NE-SW lineaments. Which also points toward the tectonic control of drainage in Palar River. As a result of channel orientation due to tectonic activity: (i) most channels are A-type or B-type associated with the lineaments, (ii) the pattern of the drainage network is dendritic, rectangular sometime trellis too, and (iii) the main rivers flow longitudinally to the predominant lineament direction.

Statistical assessment of nonpoint source pollution in agricultural watersheds in the Lower Grand River watershed, MO, USA

The water quality in many Midwestern streams and lakes is negatively impacted by agricultural activities. Although the agricultural inputs that degrade water quality are well known, the impact of these inputs varies as a function of geologic and topographic parameters. To better understand how a range of land use, geologic, and topographic factors affect water quality in Midwestern watersheds, we sampled surface water quality parameters, including nitrate, phosphate, dissolved oxygen, turbidity, bacteria, pH, specific conductance, temperature, and biotic index (BI) in 35 independent sub-watersheds within the Lower Grand River Watershed in northern Missouri. For each sub-watershed, the land use/land cover, soil texture, depth to bedrock, depth to the water table, recent precipitation area, total stream length, watershed shape/relief ratio, topographic complexity, mean elevation, and slope were determined. Water quality sampling was conducted twice: in the spring and in the late summer/early fall. A pairwise comparison of water quality parameters acquired in the fall and spring showed that each of these factors varies considerably with season, suggesting that the timing is critical when comparing water quality indicators. Correlation analysis between water quality indicators and watershed characteristics revealed that both geologic and land use characteristics correlated significantly with water quality parameters. The water quality index had the highest correlation with the biotic index during the spring, implying that the lower water quality conditions observed in the spring might be more representative of the longer-term water quality conditions in these watersheds than the higher quality conditions observed in the fall. An assessment of macroinvertebrates indicated that the biotic index was primarily influenced by nutrient loading due to excessive amounts of phosphorus (P) and nitrogen (N) discharge from agricultural land uses. The PCA analysis found a correlation between turbidity, E. coli, and BI, suggesting that livestock grazing may adversely affect the water quality in this watershed. Moreover, this analysis found that N, P, and SC contribute greatly to the observed water quality variability. The results of this study can be used to improve decision-making strategies to improve water quality for the entire river basin.

Modeling social–economic water cycling and the water–land nexus: A framework and an application

Water resources are an essential and determining factor for food production, ecosystem health, and socio-economic development. The socio–economic water cycling system is a complex adaptive system. Changes in the socio-economic system at the macro level, such as industrial transformation, technical progress, and water price reform, will have impacts on water resources utilization at the micro level. In this study, we applied the multi-region computable general equilibrium theory to build a multiple-scale socio–economic water cycling (SEWC) model for analyzing the impacts of water price reform, water reallocation schemes, and industrialization processes on water resources utilization, with particular attention being placed on the water–land nexus. Importantly, the key parameters for constructing this multiple-scale SEWC model, such as the relationships between water and land resources, vary spatially across multiple levels (i.e., the levels of river basin, county, and irrigation area). We therefore innovatively considered and estimated the key parameters firstly and then integrated them into the model to achieve more reliable simulation results. Taking the Heihe River Basin as an empirical example, the simulated results show that a 5% increase in both the surface water price and the groundwater price in Gaotai County would lead to a differing extent of the economic impact among the other counties. Consequently, an appropriate allocation scheme of water resources according to the levels of irrigation area, county, and the Heihe River Basin is imperative if water utilization pressure is to be mitigated within the entire river basin.

The paleoenvironmental reconstruction using fossil invertebrates of Zăton Lake (south-western Romania)

The Zăton Lake is a closed depressionlocated in the Ponoarele karst area (south-western Romania) formed along a tectonic-erosional window as a NE-SW corridor (250–450 m a.s.l.). In this area Mesozoic sedimentary rocks outcrop, along with the metamorphic basement of the Danubian Domain of the Southern Carpathians. The entire river basin is drained underground through the caves of Zăton (105 m in lenght) and Bulba (5 km long, developed on three levels). Flooding of the lake is temporary, during periods with high precipitation or the spring snow melting. A total of 34 samples were taken from one sedimentary section of the Zăton Lake and the diversity and abundance of fossil mites was assessed at different depths of the sediments. OSL (optical stimulated luminescence) datings and fossil mites’ determination were correlated with sediments geochemistry and rock magnetic properties and record the changes in temperature and vegetation in the area from present day to more than 2000 years ago.

Effective soil erosion control represents a significant net carbon sequestration

The debate over whether soil erosion is a carbon (C) sink or atmospheric CO2 source remains highly controversial. For the first time, we report the magnitude of C stabilization associated with soil erosion control for an entire large river basin. The soil erosion of the Yellow River basin in northern China is among the most severe worldwide. Progressive soil conservation has been implemented by the Chinese government since the 1970s, including the largest ever revegetation programme, the Grain-for-Green Project, which began in 1999. Based on compiled hydrological records and organic carbon (OC) data, together with primary production estimates, we evaluated the sequestered OC resulting from soil conservation. Compared with that at baseline in 1950–1970, in which significant soil conservation did not occur, the fate of erosion-induced OC was substantially altered in the period from 2000–2015. Approximately 20.6 Tg of OC were effectively controlled per year by soil conservation efforts. Simultaneously, the decomposition of erosion-induced soil organic carbon (SOC) declined from 8 Tg C yr−1 to current 5.3 Tg C yr−1. The reduced C emissions (2.7 Tg C yr−1) within the Yellow River basin alone account for 12.7% of the mean C accumulation acquired via forest expansion throughout all of China previously assessed. If the accumulated C in restored plants and soils was included, then 9.7 Tg C yr−1 was reduced from the atmospheric C pool during this period, which represents a tremendous C-capturing benefit. Thus, the increased C storage obtained via soil conservation should be considered in future C inventories.

Future Climate Change Projections of the Kabul River Basin Using a Multi-model Ensemble of High-Resolution Statistically Downscaled Data

In this study, we examined the future climatic changes in the Kabul River basin located in the Hindu Kush Mountain ranges of Pakistan and Afghanistan. We used the latest data set of statistically downscaled CMIP5 Global Climate Models (GCMs), i.e., NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP). The data set delivers valuable local scale, high-resolution climate change information for past and future periods (1950–2100) on a daily basis, which is very suitable for exploring future changes in mean and extremes of both temperature and precipitation. Multi-model ensemble derived from NEX-GDDP data effectively produces observed spatial patterns and magnitude of both temperature and precipitation that otherwise cannot be captured with coarse resolution GCMs. For the historical period (1975–2005), NEX-GDDP presented an improved seasonal cycle climatology and correlation coefficient with the observed data set. Future projections using multi-model ensembles indicate a consistent rise in mean temperature over the entire Kabul River Basin, relative to the baseline under RCP4.5 and RCP8.5 emission scenarios. Although the increase in temperature is not uniform across the domain, upper reaches of the basin show annual and seasonal warming of approximately 6.8 °C by the end of the twenty first century under the RCP8.5 scenario. These changes are significant at a 95% confidence level. The rise in summer and winter temperatures may negatively affect the snow accumulation during winter and has the potential to accelerate glacier melting during summers. Projections of future precipitation under both scenarios show an overall decrease in mean precipitation, particularly under the RCP8.5 scenario.

Nitrogen fluxes between the ocean and a river basin using stable isotope analysis

Total nitrogen (TN), consisting of total particulate nitrogen (TPN) and total dissolved nitrogen (TDN) pools, may be transported to the ocean not only via river channels but also from across the entire river basin via groundwater and migratory animals. Since marine derived nitrogen (MDN) is hypothesized to largely be transported in particulate form, it is necessary to investigate the contribution of particulate MDN in ground surface soils to the total MDN at the river ecosystem scale. In this study, we investigated TN export from an entire river basin to the ocean, and also estimated the contribution of pink (Oncorhynchus gorbuscha) and chum salmon (O. keta) to total oceanic nitrogen input across a river basin. The maximum potential contribution of MDN entering the river basin from the ocean as salmon was 23.8% relative to the total amount of TN exported from the river basin. The contribution of MDN from the ocean to particulate nitrogen in river basin soils was estimated to be 22.9% with standard deviation (SD) of 3.6% using stable isotope analysis (SIA) of nitrogen (δ15N).

Water replenishment for ecological flow with an improved water resources allocation model

With rapid urbanization, there will be more conflict between human systems and the river ecological system, and therefore, ecological operations, practices and research must involve the ecological water replenishment of entire river basins with new modeling tools. In this study, based on a water resource allocation and simulation model (WAS), we establish an ecological flow-oriented water resource allocation and simulation framework (E-WAS) by comprehensively considering both ecological flow constraints and ecological flow targets. To control multiple types of water sources and dynamically allocate water resources to replenish ecological water in the river, virtual reservoirs and ecological units are added to the model network. With new water balance equations for virtual reservoirs and ecological units, the E-WAS can simulate the ecological replenishment process in a river basin and can provide a recommended water replenishment scheme that considers optimization principles. The E-WAS was applied in the Pingshan River Basin, Shenzhen, China. Fourteen ecological units and 38 water supply nodes are considered in the model. A water replenishment scheme that used water from 6 reservoirs and reclaimed water from 5 water sewage plants was selected. This scheme significantly increased the satisfactory degree of ecological water demand and efficiently supported the formulation of a control scheme for the water environment of a basin. The E-WAS framework is similar to model plug-ins but helps to avoid the large workload that is required for model redevelopment and can expand the functions of core models relatively quickly.

Environmental radioactivity of soils and sediments: Egyptian sector of the Nile valley

ABSTRACTThe activity concentrations of natural 40K, 232Th, and 238U in 89 soil and 84 sediment samples collected over the entire Egyptian Nile River basin including the Nile delta are reported based on the results of epithermal neutron activation analysis. The average activity concentrations of 40K, 232Th, and 238U equal to 15.3 ± 6.6, 15.6 ± 11.1 and 220 ± 31 Bq/kg, respectively, are significantly lower than those reported for the Upper Continental Crust, World Average Sediments as well as World Average Soils, suggesting the presence of a considerable portion of mafic material, most probably originating from the Ethiopian High Plateau. Their average activity concentrations are statistically the same in soil and sediments, indicating that the Nile sediments and soil material are of the same origin. The main goal of this study was not only to estimate the radiological hazards but also to show the influence of sedimentary material transportable by the Blue Nile from the Ethiopian High Plateau. The different hazard indices like the radium equivalent, gamma index, external hazard as well as the internal hazard show a low radiological exposure either on direct contact or if local mud bricks are used in the construction of dwellings.

Economy-pollution nexus model of cities at river basin scale based on multi-agent simulation: A conceptual framework

Rapid urbanization greatly accelerated economic and social development in key river basins of China, but also created numerous environmental problems, from the local to the global scale, including increased air and water pollution and decreased water supply, local climate alteration and increased energy demands, as well as a major reduction in natural vegetation production and carbon storage/sequestration. The correlation analysis between urban economy and pollution transfer among cities in river basins has become one of highlights in current researches. Based on the Netlogo software platform, this paper establishes a correlation model among cities in the same river basin from the point of view of multi-agent simulation. Moreover, it assesses the relationship between urban economic development and pollution transfer from three aspects: network concentration; network size; link intensity. The influence of network concentration and link intensity on the total economic size and pollution transfer of the entire river basin is similar. In parallel, the influence of network size on the two modelled variables shows an opposite trend, demonstrating that network size has a greater impact on the city. By comparing the trend of economic size and pollution transfer with the change of network concentration in the context of different economic transfer thresholds, results demonstrate that, with the increase of network concentration, the influence becomes more pronounced. Appropriate error analysis was used to validate the simulation results. In particular, according to it, the error between 10-time and 20-time steps simulation is less than 10%. Consequently, the simulation results are valid. This paper, deepening the research on the correlation among river basin cities, lays the foundation for further research on the directional transmission of the economy and pollution.

Basin‐scale environmental water delivery in the Murray–Darling, Australia: A hydrological perspective

Abstract A major outstanding challenge for environmental flow management is to move from a single site, reach or river focus to planning and delivering environmental flows across entire river basins. There is a need for case studies of basin‐scale environmental water delivery as a first step in understanding and eventually generalising basin‐scale responses. The Commonwealth Environmental Water Holder manages a portfolio of water entitlements for protecting and restoring aquatic ecosystems of the Murray–Darling Basin (MDB). This article describes the strategies used by the water holder and the hydrological outcomes of their basin‐scale environmental water delivery program. There are five delivery strategies used to enhance benefits achieved with available environmental water. Although the volume of commonwealth environmental water is small relative to mean catchment inflows, improvements in baseflows and freshes are seen across the MDB. Water was also successfully delivered into floodplain wetlands. The case study provides a successful example of implementing a basin‐scale program for environmental water delivery. However, there remains a great need to improve the knowledge, governance and planning tools for managing environmental water for a broad range of ecological demands that operate at the basin‐scale.

Quantifying the streamflow response to frozen ground degradation in the source region of the Yellow River within the Budyko framework

The source region of the Yellow River (SRYR) is greatly important for water resources throughout the entire Yellow River Basin. Streamflow in the SRYR has experienced great changes over the past few decades, which is closely related to the frozen ground degradation; however, the extent of this influence is still unclear. In this study, the air freezing index (DDFa) is selected as an indicator for the degree of frozen ground degradation. A water-energy balance equation within the Budyko framework is employed to quantify the streamflow response to the direct impact of climate change, which manifests as changes in the precipitation and potential evapotranspiration, as well as the impact of frozen ground degradation, which can be regarded as part of the indirect impact of climate change. The results show that the direct impact of climate change and the impact of frozen ground degradation can explain 55% and 33%, respectively, of the streamflow decrease for the entire SRYR from Period 1 (1965–1989) to Period 2 (1990–2003). In the permafrost-dominated region upstream of the Jimai hydrological station, the impact of frozen ground degradation can explain 71% of the streamflow decrease. From Period 2 (1990–2003) to Period 3 (2004–2015), the observed streamflow did not increase as much as the precipitation; this could be attributed to the combined effects of increasing potential evapotranspiration and more importantly, frozen ground degradation. Frozen ground degradation could influence streamflow by increasing the groundwater storage when the active layer thickness increases in permafrost-dominated regions. These findings will help develop a better understanding of the impact of frozen ground degradation on water resources in the Tibetan Plateau.

GIS-based soil loss estimation using RUSLE model: a case of Kirindi Oya river basin, Sri Lanka

Soil erosion is one of the main reasons for low crop productivity. Identification of areas vulnerable to soil erosion is crucial in applying soil conservation measures especially in river basin. Kirindi Oya river basin is one of the important river basins that supply irrigation for the downstream dry zone of Sri Lanka. This study assessed the soil erosion and generated soil erosion hazard map for Kirindi Oya basin using revised universal soil loss equation (RUSLE) model in Arc GIS 10.2. Predicted soil erosion rates estimated from RUSLE model ranged from 19 to 184 t ha−1 year−1 with an average 33 t ha−1 year−1 for the entire river basin. The basin was categorized into five different erosion hazard classes, low, moderate, high, very high, and extremely high. The study revealed that majority of extremely vulnerable soil erosion areas (> 60 t ha−1 year−1) belongs to Haldummulla area in Badulla district of the basin. About 47% of the basin area in the dry zone was categorized into low erosion hazard class (< 30 t ha−1 year−1). However, these soil loss rates were above the critical soil loss rates (6.7 t ha−1 year−1) stipulated to dry zone, Sri Lanka. The results of this study may help stakeholders to implement soil conservation measures in the Kirindi Oya basin.

Recent Niger Delta shoreline response to Niger River hydrology: Conflict between forces of Nature and Humans

The Niger River Delta is a prolific hydrocarbon province and a mega-delta of economic and environmental relevance. To understand patterns of its recent shoreline evolution (1923–2013) in response to the Niger River hydrology, and establish the role played by forces of Nature and Human, available topographic and satellite remote sensing data, combined with hydro-climatic (rainfall and runoff) data were analyzed.Results indicate that the entire delta coastline dramatically receded: 82% of the >400 km-long coast retreated, during the period 1950–1987; and 69% between 2007 and 2012. Prior to 1950, there was a continuation of seaward advancement along 53–74% of the delta coast. The 1950–1987 shoreline recession coincided with occurrences of two major events in the Niger River basin; these are downward trends in hydro-climatic conditions (the great droughts of the 1970s-1980s), and dam construction on the Lower Niger River at Kainji (1964–1968). The 2007–2012 event corresponded with the extensive channel dredging during 2009–2012 in the Lower Niger River from the coastal town of Warri in the south to Baro in the north. Remarkably, the largest net shoreline advancement recorded in 74% of the entire delta area occurred within a year (2012–2013), which we link to increased sediment supply to the coast caused by the ‘2012’ floods, adjudged the worst floods in the entire Niger River Basin in the last few decades. With both anthropogenic and environmental factors inducing delta evolution, only innovative river and coastal management can determine the fortune of the future coastal development of the Niger Delta.

Changing sediment budget of the Mekong: Cumulative threats and management strategies for a large river basin

Two decades after the construction of the first major dam, the Mekong basin and its six riparian countries have seen rapid economic growth and development of the river system. Hydropower dams, aggregate mines, flood-control dykes, and groundwater-irrigated agriculture have all provided short-term economic benefits throughout the basin. However, it is becoming evident that anthropic changes are significantly affecting the natural functioning of the river and its floodplains. We now ask if these changes are risking major adverse impacts for the 70 million people living in the Mekong Basin. Many livelihoods in the basin depend on ecosystem services that will be strongly impacted by alterations of the sediment transport processes that drive river and delta morpho-dynamics, which underpin a sustainable future for the Mekong basin and Delta.Drawing upon ongoing and recently published research, we provide an overview of key drivers of change (hydropower development, sand mining, dyking and water infrastructures, climate change, and accelerated subsidence from pumping) for the Mekong's sediment budget, and their likely individual and cumulative impacts on the river system. Our results quantify the degree to which the Mekong delta, which receives the impacts from the entire connected river basin, is increasingly vulnerable in the face of declining sediment loads, rising seas and subsiding land. Without concerted action, it is likely that nearly half of the Delta's land surface will be below sea level by 2100, with the remaining areas impacted by salinization and frequent flooding. The threat to the Delta can be understood only in the context of processes in the entire river basin. The Mekong River case can serve to raise awareness of how the connected functions of river systems in general depend on undisturbed sediment transport, thereby informing planning for other large river basins currently embarking on rapid economic development.

Spatiotemporal patterns and source attribution of nitrogen pollution in a typical headwater agricultural watershed in Southeastern China

Excessive nitrogen (N) discharge from agriculture causes widespread problems in aquatic ecosystems. Knowledge of spatiotemporal patterns and source attribution of N pollution is critical for nutrient management programs but is poorly studied in headwaters with various small water bodies and mini-point pollution sources. Taking a typical small watershed in the low mountains of Southeastern China as an example, N pollution and source attribution were studied for a multipond system around a village using the Hydrological Simulation Program-Fortran (HSPF) model. The results exhibited distinctive spatio-seasonal variations with an overall seriousness rank for the three indicators: total nitrogen (TN) > nitrate/nitrite nitrogen (NOx--N) > ammonia nitrogen (NH3-N), according to the Chinese Surface Water Quality Standard. TN pollution was severe for the entire watershed, while NOx--N pollution was significant for ponds and ditches far from the village, and the NH3-N concentrations were acceptable except for the ponds near the village in summer. Although food and cash crop production accounted for the largest source of N loads, we discovered that mini-point pollution sources, including animal feeding operations, rural residential sewage, and waste, together contributed as high as 47% of the TN and NH3-N loads in ponds and ditches. So, apart from eco-fertilizer programs and concentrated animal feeding operations, the importance of environmental awareness building for resource management is highlighted for small farmers in headwater agricultural watersheds. As a first attempt to incorporate multipond systems into the process-based modeling of nonpoint source (NPS) pollution, this work can inform other hydro-environmental studies on scattered and small water bodies. The results are also useful to water quality improvement for entire river basins.

Hydrochemical characterization of a river affected by acid mine drainage in the Iberian Pyrite Belt.

This paper addresses the modelling of the processes associated with acid mine drainage affecting the Trimpancho River basin, chosen for this purpose because of its location and paradigmatic hydrological, geological, mining and environmental contexts. By using physical-chemical indicators it is possible to define the contamination degree of the system from the perspective of an entire river basin, due to its reduced dimension. This allows an exhaustive monitoring of the study area, considering the particularity that the stream flows directly into a water dam used for human supply. With such a perspective, and in order to find global solutions, the present study seeks to develop methodologies and tools for expeditious and accurate diagnosis of the pollution level of the affected stream that feeds the water reservoir. The implemented methodology can be applied to other water systems affected by similar problems, while the results will contribute to the development of the state of the art in a representative basin of the Iberian Pyrite Belt, whose pollutants' contributions are incorporated into the reservoir.

Polycyclic aromatic hydrocarbons in surface waters, sediments, and unionid mussels: relation to road crossings and implications for chronic mussel exposure

Transportation infrastructure is a prominent feature across all landscape types, and road crossings over streams are a source of pollutant influx, especially polycyclic aromatic hydrocarbons (PAH) associated with vehicle oils and fuel combustion. Freshwater mussels (Unionoida) are vulnerable to pollutants entering streams because of their sessile benthic lifestyle and their filter- and deposit-feeding exposure routes. We assessed the effect of road crossings on PAH concentrations in mussels, sediment, and water via passive sampling devices (PSDs) at 20 sites in the upper Neuse River basin of North Carolina, and investigated the utility of PSDs for estimating PAH concentrations in mussels. Road crossings significantly increased Total PAH in downstream reaches compared to upstream for all compartments sampled (P < 0.01). Total PAH in mussels were correlated with those in PSDs both upstream and downstream of road crossings (P ≤ 0.01), and PSDs provided a reliable prediction equation for mussel tissue concentrations of Total PAH (r 2 = 0.90). Overall, PAH contributions from crossings to streams in a single, relatively rural watershed are substantial and statistically significant, suggesting that the cumulative PAH influx within an entire river basin may be considerable and exert adverse effects over a chronic lifetime exposure for mussels, especially as their contributions may amplify downstream.

Water demand and ecosystem nexus in the transboundary river basin: a zero-sum game

The water demand in the upstream and downstream of a transboundary river basin varies based on the water use by the irrigation projects, dam, hydroelectricity, ecosystem, livelihood practices and household activities of the people. The study considered the case of Teesta river basin and estimates the water demand of upstream, downstream region as well as entire Teesta river basin shared by India and Bangladesh. The water productivity method exercised in the study demonstrates that 2648 and 1971 cumec water is required to fulfill the irrigation demand of command and irrigable areas, respectively, of entire Teesta basin throughout the year against 198, 1472, 793 cumec water discharge in dry, monsoon and lean season. Although there is a substantial water demand for the hydropower projects in the upstream, it is appeared that water required only by the upstream irrigation project is beyond the water supply capacity of the Trans-Himalayan river Teesta during dry and lean season. This may underpin the shortage of water in the lower riparian country, which fuels the zero-sum game in the river basin, where one player is affected by the intervention of the another player. The result from this analysis with zero-sum game perspective may be useful for reviewing transboundary water policies, basin management and development, sustainable water resource management and water sharing mechanism among countries in the transboundary river basin.