A better use of land and water resources will be necessary to meet the increasing demand for food in the Nile basin. Using a hydro-economic model along the storyline of three future political cooperation scenarios, we show that the future of food production in the Basin lies not in the expansion of intensively irrigated areas and the disputed reallocation of water, but in utilizing the vast forgotten potential of rainfed agriculture in the upstream interior, with supplemental irrigation where needed. Our results indicate that rainfed agriculture can cover more than 75% of the needed increase in food production by the year 2025. Many of the most suitable regions for rainfed agriculture in the Nile basin, however, have been destabilized by recent war and civil unrest. Stabilizing those regions and strengthening intra-basin cooperation via food trade seem to be better strategies than unilateral expansion of upstream irrigation, as the latter will reduce hydropower generation and relocate, rather than increase, food production. (C) 2016 Elsevier Ltd. All rights reserved.

In het kader van het Nationaal Modellen- en Datacentrum (NMDC) is in 2011 het NMDC innovatieproject 'Integraal waterbeheer - van kritische zone tot kritische onzekerheden' gestart (www.nmdc.eu). Dit project heeft tot doel om de modellen voor bodem, water, vegetatie en klimaat(verandering) door samenwerking beter op elkaar aan te laten sluiten, daarbij beter geschikt te maken om effecten van klimaatverandering te berekenen en om de verschillende typen onzekerheden bij dit soort studies in beeld te brengen. Het project is uitgevoerd door Alterra, Deltares, KNMI, PBL en TNO. In twee cases (Baakse Beek en Walcheren) hebben zij hun state-of-the-art modellen voor meteo, gewasgroei, vegetatie-ontwikkeling, hydrologie en geologie ingezet en aan elkaar gekoppeld. Dit rapport behandelt integraal de resultaten van het innovatieproject. De resultaten van de case voor de Baakse Beek zijn specifiek opgenomen in een NMDC deelrapport (Van Ek et al., 2012). Voor de case Walcheren wordt verwezen naar een artikel in voorbereiding (Kroes, J. et al., 2013). De resultaten bieden nieuwe inzichten in de vocht- en zouthuishouding van de bodem, potenties voor grondwaterafhankelijke natuur en groei van landbouwgewassen in het huidige klimaat en projecties voor klimaatverandering rond 2050. In het project zijn verschillende methoden toegepast om inzicht te krijgen in verschillende onzekerheden, hetgeen voor dergelijke integrale (model)studies praktische aanknopingspunten biedt voor de analyse van onzekerheden en effectieve samenwerking tussen de instituten.

Hydrologic climate change modelling is hampered by climate-dependent model parameterizations. To reduce this dependency, we extended the regional hydrologic modelling framework SIMGRO to host a two-way coupling between the soil moisture model MetaSWAP and the crop growth simulation model WOFOST, accounting for ecohydrologic feedbacks in terms of radiation fraction that reaches the soil, crop coefficient, interception fraction of rainfall, interception storage capacity, and root zone depth. Except for the last, these feedbacks are dependent on the leaf area index (LAI). The influence of regional groundwater on crop growth is included via a coupling to MODFLOW. Two versions of the MetaSWAP-WOFOST coupling were set up: one with exogenous vegetation parameters, the "static" model, and one with endogenous crop growth simulation, the "dynamic" model. Parameterization of the static and dynamic models ensured that for the current climate the simulated long-term averages of actual evapotranspiration are the same for both models. Simulations were made for two climate scenarios and two crops: grass and potato. In the dynamic model, higher temperatures in a warm year under the current climate resulted in accelerated crop development, and in the case of potato a shorter growing season, thus partly avoiding the late summer heat. The static model has a higher potential transpiration; depending on the available soil moisture, this translates to a higher actual transpiration. This difference between static and dynamic models is enlarged by climate change in combination with higher CO2 concentrations. Including the dynamic crop simulation gives for potato (and other annual arable land crops) systematically higher effects on the predicted recharge change due to climate change. Crop yields from soils with poor water retention capacities strongly depend on capillary rise if moisture supply from other sources is limited. Thus, including a crop simulation model in an integrated hydrologic simulation provides a valuable addition for hydrologic modelling as well as for crop modelling.

SIMGRO is an integration hub that connects to diverse hydrologic models. Its coupling method aims to describe the hydrologic feedbacks adequately at an acceptable cost of the increased computational load. The achieved balance between accuracy and efficiency is investigated in the paper. The coupling method centres around a shared state variable of two connecting subsystems. A prime example of such a variable is the elevation of the phreatic surface that forms the natural demarcation between the saturated groundwater flow and the unsaturated flow in the soil. In our scheme the shared variable is alternately updated by the connecting submodels, with both models using the same combined storage relationship. This method has also been implemented for the linkage between the ponding water of column models and surface water models. Using a basin-scale model, the scheme was subjected to a time-step sensitivity analysis. Results were compared to a benchmark, for which we took the same scheme, but with a short time step of 0.125d. Increasing the time step to 1d caused a numerical error of less than 5% in the simulated regional design discharge. Errors in the simulated 95th percentile of highest groundwater levels are less than 0.05m. The coupling method presented here is a key element of the Netherlands Hydrological Modelling Instrument. The current version involves half a million spatial units of 250×250m.

This report addresses the role of Waterwise as tool for eco-hydrological assessments in stakeholder negotiations on spatial planning issues. The often complex situations under uncertainty ask for a clear role for the stakeholders and Waterwise offers them a structure for iterative finding of solutions in a negotiation process. At the same time the multiple perspectives of the stakeholders on water management can by synchronised through a transparent and analytical tool like Waterwise. The crosssectoral role of Waterwise in situational decision making can be considered as an important function in the transition towards adaptive river basin management. Waterwise has been applied in 5 cases with the objective to enter into an interactive setting with the stakeholders. The applications have been made for the Beerze & Reusel, the Langbroekerwetering, and in the NeWater case study areas Kromme Rhine, Elbe and Nile.

Well‐conceived and detailed simulation of soil‐moisture processes is a prerequisite for accurate watershed‐scale modeling of water quantity and quality processes. For this purpose, Richards' equation (and its extensions) is the conceptually preferable option. Applying the equation on the watershed scale, however, may overstretch available computer resources. At the other extreme, methods based on lumping are oversimplified. Approaches are therefore needed that are efficient and just accurate enough, and that provide the required detail in the vertical column. We have developed a quasi‐steady‐state model that uses a sequence of steady‐state water content profiles for performing dynamic simulations. The appropriate profiles are—for each time level—selected on the basis of water balances at the aggregate scale of control volumes. The groundwater coupling scheme involves an iteration cycle for the phreatic storage coefficient. In the postprocessing stage, the values of state variables obtained using the coupled model are disaggregated, thus delivering pressure heads, moisture contents, and fluxes at the detailed scale of compartments of a Richards‐type model. The plausibility of the simplified approach was tested by comparing its results to those of a Richards‐type model. The results appear promising for at least three‐quarters of the area of the Netherlands with a shallow groundwater elevation (within 2 m of the soil surface) and a thin root zone (<0.5 m thick). Customizing the modeling method used to the situation conserves computational resources, allowing more room for doing sensitivity analyses. This could be instrumental for quantification of model reliability.

During the past decades human interference in regional hydrologic systems has intensified. These systems act as an integrating medium. They link climate, human activities and ecologic processes through groundwater and surface water interactions. For simulating these linkages an integrated regional hydrologic model has been coupled to an ecologic evaluation model. The simulated ecologic effects of climate change on mesotrophic riverine grasslands are clearly positive. Simulation results also indicate a high sensitivity of the peak discharges to the precipitation. For modelling the long-term development of land use and water management an integrated 'bio-economic' model has been constructed. It includes a model for the development of agriculture. Results for the autonomous development in reaction to climate change indicate a strong increase of field drainage by agriculture. This development would substantially reduce the predicted positive effects of climate change on riverine grasslands. The challenge is to guide regional developments in such a manner that opportunities for improving nature are not lost, but that at the same time the peak discharges are kept under control. Flow retardation in the 'fine arteries' of the upstream areas appear to be a viable option for the latter. The bio-economic model can provide help in anticipating on climate change through spatial planning.