Lieke van Roosmalen

Impact of climate and land use change on the hydrology of a large‐scale agricultural catchment

[1] This paper presents a quantitative comparison of plausible climate and land use change impacts on the hydrology of a large-scale agricultural catchment. An integrated, distributed hydrological model was used to simulate changes in the groundwater system and its discharge to rivers and drains for two climate scenarios (2071-2100). Annual groundwater recharge increased significantly (especially the B2 scenario), giving higher groundwater heads and stream discharges and amplifying the seasonal dynamics significantly. Owing to drier summers, irrigation volumes increased by up to 90% compared to current values. Changing the land use from grass to forest had a minor effect on groundwater recharge, whereas CO 2 effects on transpiration resulted in a relatively large increase in recharge. This study has shown that climate change has the most substantial effect on the hydrology in this catchment, whereas other factors such as irrigation, CO 2 effects on transpiration, and land use changes affect the water balance to a lesser extent.

Klimaændringer - påvirkning af grundvand og vandløb

Meget tyder pa, at vejrforholdene i fremtiden vil adskille sig fra dem, vi kender i dag. Disse aendringer i klimaet vil pavirke det hydrologiske kredslob pa en raekke punkter. Modelberegninger foretaget med en hydrologisk storskalamodel viser, at klimaaendringer kan resultere i markante effekter for grundvand og vandlob, men at geologiske forhold vil vaere styrende for, hvordan klimaaendringerne manifesterer sig pa det hydrologiske kredslob.

Effects of future climate change on groundwater in Denmark

The water supply in Denmark is entirely based on groundwater and it is therefore of concern how climate change will affect the groundwater reserves in the future. We have analyzed this problem by retrieving climatological output data from a regional climate model and using this data in a distributed hydrological model, focusing on a selected watershed in the country. Global climate models simulate the global climate system with greenhouse gas concentrations representing observed and possible future conditions, but their limited regional detail makes them less suitable for hydrological impact studies. Therefore, regional climate models with a limited model domain and higher resolution are utilized. In this study the regional climate model HIRHAM from the Danish Meteorological Institute is used with boundary conditions generated by the global climate model HadAM3H from Hadley Centre. The concentrations of greenhouse gas and aerosols, have been applied based on the IPCC SRES A2 emission scenario. The climate model output consists of data for two time slices, one for a period representing recent climate (1961-1990; control run) and one for the future climate (2071-2100; scenario run). The climate output used is daily precipitation, temperature and potential evapotranspiration, all at a 12x12 km resolution. Climate models are subject to systematic biases, so climate model data cannot be used directly in hydrological models. Different transfer methods exist to transfer the signal of climate change, of which two will be examined in this study. One is the so-called delta change approach, that alters the original hydrological model input data with a factor deduced from the climate model output data to generate the input data for the hydrological simulation of the future scenario. The other method is the direct method, that uses the climate model output directly as input for the hydrological model after correcting the climate output with factors based on the bias between the climate model control scenario data and the original hydrological model input data. We use the so-called DK model as the model for the hydrological analysis. The DK- model divides Denmark into 10 regions and it is based on the distributed hydrological model code MIKE SHE with a horizontal spatial discretization of 1 x 1 km2. One of these regions has been selected as the study area for the impact analysis.