Analysis of catchment response for regional water systems in the Netherlands

The very wet conditions of recent years in the Netherlands have made it clear that measures will have to be taken in this century to prevent flooding. The anticipated climate change and rise in sea level will have a crucial effect on the functioning of the surface water system. This paper reports on a project carried out as part of the national study “Water Management in the 21 st Century” to predict the changes in peak discharge resulting from climate change and to assess the efficiency of certain mitigation measures. A scenario study was set up, using a modelling approach to quantify the effects of climate change and mitigation measures. The discharge calculated for the present situation was used as a reference. The climate scenario represented the period 2050 to 2100, which is expected to be warmer and wetter and will result in higher peak flows. Five mitigation measures to reduce these peak flows were studied. The SIMPRO model was used because it simulates shallow groundwater flow locally and water flow in a network of water courses regionally. SIMPRO is physically-based and can therefore be used in situations with changing hydrological conditions. The discharge analysis was done for five regions of the Netherlands, ranging in size from 25 to 142 km 2 and representing the major landscape areas of the Netherlands. Two of the areas were in the higher-lying part of the country. The results suggest that climate change in the Netherlands would increase peak discharges by 10 to 20%. Of the five mitigation measures analysed, reducing peak discharges by gates or culverts was found to be very effective; it could cancel out the effect of climate change. Less effective measures would be to increase the area of open water or the flow resistance.