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Accelerating future water shortages require development of operational water governance models, as illustrated by three case studies: (1) upstream–downstream interactions in the Aral Sea basin, where science acts as problem recognizer, emphasizing scoping policies; (2) impact and adaptation of climate change on water and food supply in the Middle East and North Africa, where science acts as a mediator between perspectives, emphasizing scoping and a start of implementation policies; and (3) green water credits in Kenya, where science acts as advocate, emphasizing scoping and implementation policies in close interaction with stakeholders, including impulses from applied to basic research. [ABSTRACT FROM AUTHOR]

Food production, water availability and energy production are important ecosystem services of the Upper Tana basin (Kenya) and they decline due to upstream erosion affecting downstream water users. The effect of 11 soil conservation measures on soil erosion and the three ecosystem services was estimated by a modelling approach to assess agro-ecological processes and benefit/cost relations. Soil water available for evaporation and transpiration (‘green water’) functioned as a unifying concept to express the effects of erosion and the impacts of soil and water conservation measures that result in: (1) increased water availability for crops; (2) increased fluxes towards aquifers, thereby increasing water supply and regulating streamflow, and (3) a reduction of erosion and siltation of reservoirs used for hydroelectricity. Modelling indicated that the three ecosystem services could be improved, as compared with the base level, by up to 20% by introducing appropriate conservation measures with benefit/cost relations of around 7. However, farmers were unable to make the necessary investments and much effort and many institutional studies were needed to achieve progress towards implementation by initiating the Green Water Credits (GWC) programme intended to arrange payments by downstream businesses to upstream farmers. A timeline analysis is presented to illustrate the slow, but persistent, development of transdisciplinary activities as a function of time usingconnected value developmentas a guiding principle. [ABSTRACT FROM AUTHOR]

There is a growing awareness that water will be one of the most critical natural resources and that there is a need for better management of the limited water resources. This paper reports on a study of a water-scarce river basin in western Turkey. Hydrological analyses, emphasizing water use for irrigation, are performed at three different spatial scales (field scale, irrigation scheme scale and basin scale) using two kind of model: a parametric basin-scale model and a physically based crop-scale model. Data accessibility for this basin, especially for areal data, was low. A combined use of public domain data sets and remotely sensed data was used to solve this problem. A public domain digital elevation model was used to generate the streamflow network and the distances and slopes to streams. Land-cover data and leaf area index data were derived from public domain NOAA?AVHRR images. For one irrigation scheme in the basin, detailed areal water balances were obtained from the simulation model and a comparison was made between a normal and a water-short year. At the basin scale, observed flows were compared with simulated flows. It is concluded that remotely sensed data and other public domain data can be used with simulation models at different scales to create a powerful tool to evaluate water resources in a basin context. [ABSTRACT FROM AUTHOR]

The Kuş Cenneti is a wetland in the Gediz River Delta in Turkey. Part of it needs a large supply of low saline water to ensure the survival of endangered bird species. Any increase must be supplied at the expense of the upstream irrigated agriculture. The effects of basin water reallocation on water availability and crop productivity were evaluated using a semi-distributed hydrological model (SLURP). It was found that, during the irrigation season, increased wetland water demand causes increased loss in yield to irrigated agriculture and, outside this period, the water supply is limited by the Gediz River minimum base flow. [ABSTRACT FROM AUTHOR]

Water managers around the world face the increasingly challenging task to evaluate the impacts of technological measures and policy mechanisms from the local to the river basin scale. A toolset providing quantitative, actionable information on dependencies and trade-offs between upstream and downstream water users is currently lacking. Yet, any intervention needs to be assessed in terms of consequences for downstream water users. This study evaluates the potential of a tracer-like approach, implemented in the water allocation software WEAP, to quantitatively track return flows and their downstream reuse in the river basin context. The WEAP-Virtual Tracer (WEAP-VT) approach was successfully applied to one of Europe's driest river basins, the Segura River Basin in Spain. For each water demand site, the different original sources of water supply, dependency on upstream return flows, and downstream reuse of its return flow were assessed. Based on these results, agricultural, urban, and environmental water users were evaluated in terms of their suitability for water saving measures and their vulnerability to the reduction in upstream return flows. A scenario analysis simulating the improvement of local efficiency improvements shows that specific irrigation schemes and ecosystems become deprived of water. Hence, efficiency improvement in water-scarce basins should be considered with caution. The demonstrated ability to quantify key water reuse indicators for individual water users and at different aggregation levels makes WEAP-VT a valuable tool to support water resource management decisions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Iran, Morocco and Saudi Arabia will face water shortages in 2040–2050. [•] Water shortages in Iran are most sensitive to climate change due to agriculture. [•] In most cases, supply enhancement is too expensive and demand has to be reduced. [ABSTRACT FROM AUTHOR]