Natural Discharge Research Articles

Factors controlling the past ~150-year ecological dynamics of Lake Wuliangsu in the upper reaches of the Yellow River, China

Lacustrine ecosystem history since the industrial revolution provides important evidence of natural versus anthropogenic effects on the environment. With high-resolution sedimentary core samples and organic–inorganic geochemical methods, we reconstruct the past ~150-year ecosystem evolution of Lake Wuliangsu in the upper reaches of the Yellow River, and probe factors controlling the ecological dynamics. In this study, ecological changes in Lake Wuliangsu over the past ~150 years were identified. After the lake formed in the 1850s, biological productivity of the lake was still under-developed until the 1950s. During the period of 1950s–1970s, submerged macrophytes became the dominant organisms in the lake because of lake area expansion and slight increases of nutrient input from agricultural development in the catchment. The domination of submerged macrophytes ceased after the 1970s, which was possibly induced by the shrinkage of the lake area. After the 1990s, the main contributor of sedimentary n-alkanes most likely shifted to reeds because of eutrophication caused by anthropogenic activities. The results clearly demonstrate that the ecosystem in Lake Wuliangsu before the 1950s strongly depended on the natural discharge, whereas at later stages, it was significantly influenced by human activities. During the period of 1950s–1990s, the human-monitored lake area seems to be the main factor in the lake ecosystem evolution. However, when the nutrient supply went beyond the tipping point after the 1990s, eutrophication took over and played a key role in the lake ecosystem evolution.

Adsorption of arsenic by natural pozzolan in a fixed bed: Determination of operating conditions and modeling

The presence of arsenic at relatively high concentrations in water as a result of natural and human activity discharges requires proper treatment before use. Arsenic was analyzed using a spectrophotometric method. Experiments were carried out in a column packed with natural pozzolan (black, red) from Djoungo (Cameroon) at different pH (5, 7, 9), initial arsenic concentration (100μg/L, 200μg/L, 400μg/L) and flow velocity (0.39cm/min, 0.79cm/min, 1.57cm/min). Results showed that the bed saturation time (outlet concentration from the bed≥10μg/L) is longer for a lower pH, flow velocity and initial arsenic concentration. Two kinetics models; Adams-Bohart and Thomas were applied to the experimental data to predict the breakthrough curves using linear regression and to determine the characteristic parameters of the column. The Thomas model was found appropriate for the description of the whole breakthrough curves, whereas the Adams–Bohart model could only predict the initial part of the breakthrough curves. Using water with low arsenic concentration, pozzolan demonstrated its effectiveness in arsenic removal below the acceptable level (10μg/L).

Definición de zonas de recarga y descarga de agua subterránea a partir de indicadores superficiales: centro-sur de la Mesa Central, México

The aim of this paper is the delimitation of groundwater recharge and discharge zones in the centre-south portion of the Mesa Central. This was achieved using groundwater flow systems theory, which has proved to be a valuable tool since it considers a systemic perspective of the environment, integrating several natural elements. There are various physical, chemical and biological processes generated in the subsoil within which groundwater is incorporated. This involvement is caused by the natural gravitational movement of groundwater which is manifested on the surface by contrasting evidences in the recharge and discharge zones. Therefore, the objective of this paper includes the demonstration of the usefulness of the analysis of those indicators to locate priority areas and also provides an approximation of groundwater functioning. The definition of recharge and discharge zones included the analysis of maps describing soil type, vegetation, topographic elevation, groundwater flowpath direction, springs, and presence of natural water bodies. Such analysis was carried out through the overlaying tool of ArcMap™ software. The results suggest that the highlands of Fría, San Miguelito and Santa Bárbara as recharge zones. Natural discharge zones were originally present in the plain of the Aguascalientes tectonic depression, and some flat and topographic low zones in the vicinity of Altos de Jalisco, Santa María del Río and Ojuelos.

A global data set of the extent of irrigated land from 1900 to 2005

Abstract. Irrigation intensifies land use by increasing crop yield but also impacts water resources. It affects water and energy balances and consequently the microclimate in irrigated regions. Therefore, knowledge of the extent of irrigated land is important for hydrological and crop modelling, global change research, and assessments of resource use and management. Information on the historical evolution of irrigated lands is limited. The new global historical irrigation data set (HID) provides estimates of the temporal development of the area equipped for irrigation (AEI) between 1900 and 2005 at 5 arcmin resolution. We collected sub-national irrigation statistics from various sources and found that the global extent of AEI increased from 63 million ha (Mha) in 1900 to 111 Mha in 1950 and 306 Mha in 2005. We developed eight gridded versions of time series of AEI by combining sub-national irrigation statistics with different data sets on the historical extent of cropland and pasture. Different rules were applied to maximize consistency of the gridded products to sub-national irrigation statistics or to historical cropland and pasture data sets. The HID reflects very well the spatial patterns of irrigated land as shown on historical maps for the western United States (around year 1900) and on a global map (around year 1960). Mean aridity on irrigated land increased and mean natural river discharge on irrigated land decreased from 1900 to 1950 whereas aridity decreased and river discharge remained approximately constant from 1950 to 2005. The data set and its documentation are made available in an open-data repository at https://mygeohub.org/publications/8 (doi:10.13019/M20599).

Using hydrological simulation to detect human-disturbed epoch in runoff series.

Runoff in major rivers in China has been decreasing in recent decades, mainly due to climate change and human activity. River basin managers have a critical interest in detecting and diagnosing non-stationaries in runoff time series. Here we use a rainfall runoff model-based approach to identify the human-disturbed periods of the record. The method is applied to the Kuye River catchment, located in the Loess Plateau, China. The SimHyd model performs well for simulation of monthly natural discharges, and the method suggests that discernable human influence began in 1980. Anthropogenic effects were detectable several years earlier at the downstream stations than the upstream stations, consistent with pace and timing of soil and water conservation measures implemented across the Kuye River catchment.

Rocket‐triggered lightning propagation paths relative to preceding natural lightning activity and inferred cloud charge

AbstractLightning Mapping Array (LMA) data are used to compare the propagation paths of seven rocket‐triggered lightning flashes to the inferred charge structure of the thunderstorms in which they were triggered. This is the first LMA study of Florida thunderstorm charge structure. Three sequentially (within 16 min) triggered lightning flashes, whose initial stages were the subject of Hill et al. (2013), are reexamined by comparing the complete flashes to the preceding natural lightning to demonstrate that the three rocket‐triggered flashes propagated through an inferred negative charge region that decreased from about 6.8 to about 4.4 km altitude as the thunderstorm dissipated. Two other flashes were also sequentially triggered (within 9 min) in a thunderstorm that contained a convectively intense region ahead of a stratiform region, with similar observed results. Finally, two unique cases of triggered lightning flashes are presented. In the first case, the in‐cloud portion of the triggered lightning flash, after ascending to and turning horizontal at 5.3 km altitude, just above the 0°C level, was observed to very clearly resemble the geometry of the in‐cloud portion of the preceding natural lightning discharges. In the second case, a flash was triggered relatively early in the storm's lifecycle that did not turn horizontal near the 0°C level, as is usually the case for triggered lightning in dissipating storms, but ascended to nearly 7.5 km altitude before exhibiting extensive horizontal branching.

Water discharge affects Atlantic salmon Salmo salar smolt production: a 27 year study in the River Orkla, Norway.

A model that explains 48% of the annual variation in Atlantic salmon Salmo salar smolt production in the River Orkla, Norway, has been established. This variation could be explained by egg deposition, minimum daily discharge during the previous winter and minimum weekly discharge during the summer 3 years before smolt migration. All coefficients in the model were positive, which indicates that more eggs and higher minimum discharge levels during the winter before smolt migration and the summer after hatching benefit smolt production. Hence, when the spawning target of the river is reached, the minimum levels of river discharge, in both winter and summer, are the main bottlenecks for the parr survival, and hence for smolt production. The River Orkla was developed for hydropower production in the early 1980s by the construction of four reservoirs upstream of the river stretch accessible to S. salar. Although no water has been removed from the catchment, the dynamics of water flow has been altered, mainly by increasing discharges during winter and reducing spring floods. In spite of the higher than natural winter discharges, minimum winter discharge is still a determinant of smolt production. Hence, in regulated rivers, the maintenance of discharges to ensure that they are as high as possible during dry periods is an important means of securing high S. salar smolt production.

Groundwater in hard rocks of Benin: Regional storage and buffer capacity in the face of change

Groundwater plays a major role in supplying domestic water to millions of people in Africa. In the future, the ability to increase reliable water supplies for domestic and possibly irrigation purposes will depend on groundwater development. Groundwater storage is a key property because it controls the buffering behavior of the aquifer as it is subjected to time-varying conditions such as increased pumping or land-use change. However, quantitative knowledge of groundwater storage in Africa is very limited. This lack of knowledge is a major concern in hard rocks, which cover about 40% of the surface area of Africa. This paper presents a unique quantitative assessment of groundwater storage in different types of hard rocks and a first estimate of the capacity of hard rock aquifers to buffer changes in climatic and anthropogenic conditions. Our study area in Benin (West Africa) is composed of various grades of metamorphic rocks. We used the latest developments in the application of the magnetic resonance geophysical method to confront the methodological difficulty of quantifying groundwater storage. We successfully conducted 38 magnetic-resonance measurements in eight (8) different geological units; each measurement was quantitatively interpreted in terms of groundwater storage. We determined the groundwater storage of our study area to be 440 mm ± 70 mm (equivalent water thickness). To assess the buffer capacity of aquifers, we compared groundwater storage to groundwater discharge. Groundwater discharge is the sum of natural discharge plus human abstraction. We estimated natural discharge (i.e. deep drainage plus evapotranspiration) from water table fluctuations monitored in six (6) piezometers. Human abstraction was calculated based on the number of operating boreholes and their average daily abstraction. We found that human abstraction (0.34 mm/year ± 0.07 mm) is far less than natural discharge (108 mm/year ± 58 mm). We conclude that increased abstraction due to population growth will probably have a smaller impact on storage than observed land-use change, which may lead to a change in the evapotranspiration rate. We calculated buffer capacity as the ratio of current storage to total discharge, and obtained a result of 6 years ± 47 months. This buffer capacity confirms groundwater’s ability to buffer changes. Finally, our study is intended to promote a more quantitative approach to assessing groundwater resources in Africa and to support our ability to adapt to current and future changes.

Potential impacts of climate change and regional anthropogenic activities in Central European mesoscale catchments

The Soil and Water Integrated Model (SWIM) was used to assess potential climate and land-use change impacts in the Central European catchments of Schwarze Elster, Spree and Lusatian Neisse which are heavily influenced by opencast lignite mining. To account for potential climate change, scenarios of two statistical regional climate models, STAR and WettReg, were used. Regional anthropogenic change was considered in terms of increasing cultivation of energy crops (oilseed rape, silage maize, sunflower and sorghum) and decreasing mining activities (decreasing groundwater depression cone). In the climate scenarios, decreased natural discharge, by up to 60% in the long-term average, was simulated. In simulations with climate scenarios and oilseed rape, this effect is halved; the other energy crops have a small additional impact on discharge. The decreasing groundwater depression cone slightly compensates for climate change impacts. Overall, potential impacts of regional anthropogenic activities are secondary to those of climate change.Editor Z.W. Kundzewicz; Guest editor M. White

Assessment of Dewatering Requirements and their Anticipated Effects on Groundwater Resources: A Case Study from the Caldag Nickel Mine, Western Turkey

Dewatering requirements of three open pits located in western Turkey and the impact of dewatering on groundwater resources were evaluated using a three-dimensional numerical groundwater flow model. The groundwater was modeled using MODFLOW software and the dewatering was simulated using the MODFLOW Drain Package. The drain cell configurations were determined by pit boundaries; invert elevations of drains corresponded to the bench elevations in the mining schedule, which varied dynamically among the three pits. Transient model runs were conducted for the 21 years of mine life to calculate the monthly dewatering rates. Simulation results indicate that the average groundwater inflow to the excavations is 3.64 L/s, excluding the effects of direct rainfall into the pits and surface water flow from the benches. Long term (80 years) simulations were conducted to predict the amount of drawdown at the water supply wells in the area. The results indicate that 21 years of mining will not significantly impact the water levels in these wells. However, natural discharge from the springs near the pits will be exhausted by the dewatering.

A stepped leader model for lightning including charge distribution in branched channels

The stepped leader process in negative cloud-to-ground lightning plays a vital role in lightning protection analysis. As lightning discharge usually presents significant branched or tortuous channels, the charge distribution along the branched channels and the stochastic feature of stepped leader propagation were investigated in this paper. The charge density along the leader channel and the charge in the leader tip for each lightning branch were approximated by introducing branch correlation coefficients. In combination with geometric characteristics of natural lightning discharge, a stochastic stepped leader propagation model was presented based on the fractal theory. By comparing simulation results with the statistics of natural lightning discharges, it was found that the fractal dimension of lightning trajectory in simulation was in the range of that observed in nature and the calculation results of electric field at ground level were in good agreement with the measurements of a negative flash, which shows the validity of this proposed model. Furthermore, a new equation to estimate the lightning striking distance to flat ground was suggested based on the present model. The striking distance obtained by this new equation is smaller than the value estimated by previous equations, which indicates that the traditional equations may somewhat overestimate the attractive effect of the ground.

On the droplet velocity and electrode lifetime of digital microfluidics: voltage actuation techniques and comparison

The distinct manageability of digital microfluidics (DMF) has rendered it a promising platform for building large-scale micro-reactors on a single chip for closed-loop automation. However, the limited velocity of the droplet transportation has hindered DMF from being utilized in high-throughput applications. This work investigates a control-engaged droplet actuation technique involving regular electronic hardware and computer-based software to simultaneously raise the velocity of the droplet transportation and elongate the electrode lifetime by lowering the root-mean-square value of the actuation voltage. The technique is based on a series of direct current (DC) pulses and multi-cycles of natural discharge coordinated with the droplet dynamic motions, facilitating real-time droplet position sensing. We found that the proposed technique was superior to both DC and AC in terms of the velocity. As to the electrode lifetime, all showed excellent performance under normal dielectric coating conditions, while AC (alternating current) performed the best under critical conditions. Altogether, this work exhibits a control-engaged electrode-driving scheme with a higher velocity and a longer lifetime compared with traditional DC actuation and for the first time provides a fundamental comparison among the techniques engaging different actuation signals.

Water discharge variability of Changjiang (Yangtze) and Huanghe (Yellow) Rivers and its response to climatic changes

Infl uences of large-scale climatic phenomena, such as the El Nino/La Nina-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), on the temporal variations of the annual water discharge at the Lijin station in the Huanghe (Yellow) River and at the Datong station in the Changjiang (Yangtze) River were examined. Using the empirical mode decomposition-maximum entropy spectral analysis (EMDMESA) method, the 2- to 3-year, 8- to 14-year, and 23-year cyclical variations of the annual water discharge at the two stations were discovered. Based on the analysis results, the hydrological time series on the interannual to interdecadal scales were constructed. The results indicate that from 1950 to 2011, a significant downward trend occurred in the natural annual water discharge in Huanghe River. However, the changes in water discharge in Changjiang River basin exhibited a slightly upward trend. It indicated that the changes in the river discharge in the Huanghe basin were driven primarily by precipitation. Other factors, such as the precipitation over the Changjiang River tributaries, ice melt and evaporation contributed much more to the increase in the Changjiang River basin. Especially, the impacts of the inter-annual and inter-decadal climate oscillations such as ENSO and PDO could change the long-term patterns of precipitation over the basins of the two major rivers. Generally, low amounts of basin-wide precipitation on interannual to interdecadal scales over the two rivers corresponded to most of the warm ENSO events and the warm phases of the PDO, and vice versa. The positive phases of the PDO and ENSO could lead to reduced precipitation and consequently affect the long-term scale water discharges at the two rivers.

석면슬레이트 설치 경과년도에 따른 두께변화 분석 및 석면섬유 자연발생량 예측모델 개발

Asbestos was one of those most frequently-used materials in constructions in Korea and 96% of the asbestos imported in the 1970's was used as a raw material of slates. However, when this asbestos gets absorbed into human bodies, it would cause some severe diseases. Researches on asbestine dust discharge are now considered to be carried out only immediately and in Korea, fortunately, those researches on the asbestine dust discharge are being actively conducted. Even so, no study, so far, has discussed asbestos fiber discharge amount through years since a first installation of a slate. In consideration of that, in the concerned study, a total of 135 buildings which were built with slates, were observed as research subjects. Next, by databasing the data and using SPSS, the study looked into changes in thickness of the slates in the buildings through years since the first installations of the slates and also developed a model to forecast asbestos fiber discharge amount. As a result, Point A(end) was observed to discharge more asbestine dust than Point B(middle) by 0.014mm every year. In terms of the underneath of the troughs, the concerned part was understood to discharge more asbestine dust than narrow corridors by 0.004mm every year. The annual average asbestine dust discharge through years turned out to be 0.033mm and a functional formula to forecast natural discharge amount of the asbestos fiber was gained as (21.83 + 5.5 <TEX>${\times}$</TEX> a number of years since the installation)<TEX>$g/m^2$</TEX>. The findings of the study will be used to forecast a total amount of asbestos fiber discharge nationwide in the future.

Natural discharge after pulse and cooperative electrodes to enhance droplet velocity in digital microfluidics

Digital Microfluidics (DMF) is a promising technology for biological/chemical micro-reactions due to its distinct droplet manageability via electronic automation, but the limited velocity of droplet transportation has hindered DMF from utilization in high throughput applications. In this paper, by adaptively fitting the actuation voltages to the dynamic motions of droplet movement under real-time feedback monitoring, two control-engaged electrode-driving techniques: Natural Discharge after Pulse (NDAP) and Cooperative Electrodes (CE) are proposed. They together lead to, for the first time, enhanced droplet velocity with lower root mean square voltage value.

Response of Orthoptera communities to succession in alluvial pine woodlands

During the past 150 years forest management has dramatically altered in Central European woodlands, with severe consequences for biodiversity. Light forests that fulfilled variable human demands were replaced by dark high forests that function solely as wood plantations. In the Alps, by contrast, open woodlands are still present because the traditional land use as wood pasture has remained and physiographical conditions favour natural dynamics. The aim of our study was to investigate the effects of succession on the Orthoptera communities of alluvial pine woodlands in the northern Alps. Orthoptera showed a clear response to succession, with each successional stage harbouring a unique assemblage. The influence of succession on species richness and abundance were identical: The values were highest in the intermediate and lowest in the late seral stage. The diversity and abundance peak in the mid-successional stage probably reflects a trade-off between favourable ambient temperatures for optimal development and sufficient food, oviposition sites and shelter against predators. Food shortage and easy access for predators seemed to be limiting factors in the early successional stage. In contrast, in the late successional stage adverse microclimatic conditions probably limit Orthoptera occurrence. Although all three successional stages of the pine woodlands are relevant for conservation, the early and mid-successional stages are the most important ones. Conservation management for Orthoptera in this woodland type should aim at the reintroduction of cattle grazing and the restoration of the natural discharge and bedload-transport regimes of the alpine rivers.

Determination of Optimal River Network from DEM using differential GPS

In this study, the Optimal River Network (ORN) has been determined in a waterlogged area. A dense 3D coordinates obtained from Differential GPS were used to create a Digital Elevation and Digital Terrain Models and their contingents comprising Watershed, Slope, Contours and Aspect. Areas at risk of being flooded are northward, surrounded by lowlying terrain while the south constitute undulating hills with natural river discharge at the centre. The ORN determines an ideal direction of flow of water out of the region, putting into consideration future planning and development. Existing small streams are directed to a permanent flow network to minimise land loss due to erosion and reduce cost of developing building projects in the waterlogged area. It is evident here that Differential GPS and Geographic Information Systems software can be combined to find ideal solutions to natural hazards akin to flood and erosion and even beyond.

Investigation of Boron Pollution in the Gediz River

This study was conducted to determine the concentration of boron in the waters of the Gediz River. According to the results, the boron concentrations ranged from 0.125 to 4.548 mg/L. The average boron value (2.428 mg/L) was compared with “Environmental Regulations, Water Pollution Control Regulations and Quality Criteria for Inland Water Resources by Class”. The Gediz River was determined as class IV (very polluted) in terms of the boron parameters. It was concluded that the reason for the high boron values were natural and/or industrial discharges at some stations.

Physicochemical properties of aquatic habitats from ecology and civil engineering perspectives

Aquatic environments are usually represented by physicochemical properties, including flow regime on riverbed configurations, sediment size and stability, and water quality. This monograph focuses on the habitat of submerged macrophytes. Recent changes to the aforementioned physicochemical properties because of human activities have altered the aquatic habitats for submerged macrophytes, resulting in increases in the number of invasive species and extinction of native species. The expansion of invasive species into new environments often changes the physicochemical properties of these environments through accumulation of fine materials or changes in water quality. This is especially true in stable water areas— such as spring-fed rivers, rivers from lakes, lakes, and lagoons—where the submerged macrophytes are often found. In these locations, sufficient natural discharge and floods sizeable enough to renew the aquatic environment cannot be expected. In this case, increases in underwater invasive species tend to have further negative impacts on the natural environment, as they create conditions that are more suitable to themselves. These areas are considered to be among the most sensitive environments to human influences. In order to overcome this issue, it is necessary to understand the factors that limit the growth of both invasive and native endangered species. With this knowledge, it may be possible to predict future changes to physicochemical properties—focusing on limiting factors with and without the use of some countermeasures—in order to find effective management strategies. Thus, the cooperation of ecologists and civil engineers is essential in order to integrate their knowledge. To that end, all studies introduced here were presented and discussed at the annual meeting of the Ecology and Civil Engineering Society held in Saitama Prefecture, Japan, in 2009. The essential contributions made by several researchers to this issue are summarized here. Shinohara et al. (2013) point out the importance of carbon dioxide (CO2) and light availability to the distribution of submerged macrophytes. Takahashi and Asaeda (2012) clarify that low pH spring water increases the growth rate of Egeria densa by affecting free CO2 concentration in water. It is known that submerged macrophytes play an important role in the ecosystems of shallow lakes and stable streams by changing water quality, creating a refuge for other creatures, reducing bottom shear stress by stabilizing the substrate, and reducing the presence of suspended particles. Submerged macrophytes, however, have been disappearing, and the cause is purported to be a limited supply of photosynthetically active radiation (PAR) because of phytoplankton blooms. Therefore, studies showing the importance of free CO2 are of interest to those who seek to develop the above-mentioned management strategies. Matsui (2012) presents his study on the distribution and habitat of submerged macrophytes in the Seta River as it flows out of Lake Biwa, Shiga Prefecture, Japan. He introduces the clear relationship between sediment type and submerged macrophytes. The study by Gunaratne et al. (2012). addresses changes in lagoon morphology, specifically inlet morphology and flushing properties of Koggala Lagoon, Sri Lanka. According to this study, the flushing half-life, which is the time needed to replace half T. Chibana (&) Department of Civil Engineering, The University of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo 113-8656, Japan e-mail: chibana@hydra.t.u-tokyo.ac.jp

Water quality, potential conflicts and solutions—an upstream–downstream analysis of the transnational Zarafshan River (Tajikistan, Uzbekistan)

The Central Asian countries are particularly affected by the global climate change. The cultural and economic centers in this mostly arid region have to rely solely on the water resources provided by the rapidly melting glaciers in the Pamir, Tien-Shan and Alay mountains. By 2030, the available water resources will be 30 % lower than today while the water demand will increase by 30 %. The unsustainable land and water use leads to a water deficit and a deterioration of the water quality. Documenting the status quo of the water resources needs to be the first steps towards an integrated water resource management. The research presented here provides a detailed overview of the transboundary Zarafshan River, the lifeline for more than six million people. The findings are based on field measurements, existing data from the national hydrometeorological services and an extensive literature analysis and cover the status quo of the meteorological and hydrological characteristics of the Zarafshan as well as the most important water quality parameters (pH, conductivity, nitrate, phosphate, arsenic, chromate, copper, zinc, fluoride, petroleum products, phenols and the aquatic invertebrate fauna). The discharge of the Zarafshan is characterized by a high natural discharge dynamic in the mountainous upper parts of the catchment and by sizeable anthropogenic water extractions in the lower parts of the catchment, where on average 60.6 % of the available water is diverted for irrigation purposes in the Samarkand and Navoi provinces. The water quality is heavily affected by the unsustainable land use and inadequate/missing water purification techniques. The reduced discharge and the return flow of untreated agricultural drainage water lead to a critical pollution of the river in the lower parts of the catchment. Additional sources of pollutants were identified in the Navoi special economic area and the mining industry in the Tajik part of the catchment. The impact of the global climate change and the socio-economic growth on the water availability and the water demand will aggravate the detected problems and might lead to severe local and transboundary upstream–downstream water conflicts within the next decades.