Predicting Impact of Climate Change on Groundwater Dependent Ecosystems.

Groundwater plays a vital role in sustaining Groundwater Dependent Terrestrial Ecosystems (GWDTEs). As groundwater resources are controlled by long-term climate conditions, climate changes are potentially threatening these ecosystems. This paper presents a methodology to predict the potential impact of climate change on quantitative groundwater characteristics determining GWDTEs. The developed methodology includes coupling a distributed hydrological model with a transient groundwater flow model and is tested for the Kleine Nete basin, Belgium. Because the occurrence of phreatophytes is strongly determined by the dynamic properties of the groundwater system, a groundwater flow model with a high temporal and spatial distribution was developed using MODFLOW. The groundwater recharge and river heads are estimated with the WetSpa model using a daily timestep to incorporate the impact of changes in rainfall intensity. Potential future hydrological changes are calculated by comparing the hydrological state corresponding to 1960-1991 with future scenarios developed for 2070-2101. Since the uncertainty in the prediction of the future climate components such as potential evapotranspiration (PET) and precipitation is still high an ensemble of 28 climate scenarios were chosen from the PRUDENCE database. For each of these scenarios the recharge, river stage, groundwater head and groundwater flow are estimated for 32 years with half monthly timesteps. Comparison of the original measured PET with future PET shows that the PET during summer rises in all future scenarios with about 1 mm day-1. For winter conditions the scenarios predict little change in PET. Future precipitation shows an increase in precipitation during winter and a decrease during summer. Future groundwater recharge decreases on average with 20 mm year-1, the highest decreases are simulated from July until September. Average groundwater heads indicate an average decrease of 7 cm. Groundwater levels in interfluves generally show decreases up to 30 cm. The mean lowest groundwater level decreases on average with 6 cm, while the mean highest groundwater level decrease about 3 cm. On average the groundwater discharge reduces with 4%, from 5 to 4.8 m³ s-1. GWDTEs that currently receive a low groundwater discharge, are likely to disappear due to future climate changes.

Publication year:2010