Evaluation of adaptation measures to counteract rising groundwater levels in urban areas in response to climate change

For an increasing number of urban areas in Denmark and other countries with a temperate climate, large seasonal variations in precipitation, evaporation, and groundwater recharge cause problems with high groundwater levels during winter for private house owners, industry, public institutions, and infrastructure. Several factors contribute to the problem, e.g., an increase in winter precipitation, renovation of old leaky sewer pipes (previously acting as drain systems), and closure of groundwater abstraction for drinking water in urban areas in response to pollution. Four adaptation measures are compared with a detailed hydrological model for the town of Sunds, located in the western part of Denmark. Two ‘grey’, one ‘green’ and one ‘blue’ measure are evaluated. The grey solutions involve (1) installing drainage pipes (a third pipe) alongside the existing sewer pipes, and (2) lowering the water table by groundwater pumping from shallow wells, including storage of water in deeper aquifers for use in the drier summer; the green solution involves planting new forest in and around the town; and the blue solution is to establish a new ditch in the town. A climate model that projects more precipitation, especially in the winter, is used to evaluate the robustness of the different measures in a wetter climate for the northern European area. The hydrological modelling shows that the third pipe is the most effective climate-change adaptation of the four measures tested. The new ditch is an effective solution to lower the water table but with a more limited areal coverage.