Modeling Future Climate Change Impacts on Groundwater in Mountainous Valley-Bottom Aquifers
Abstract
Groundwater resources within many mountainous valley-bottom aquifers are increasingly threatened by increased demand for water due to population growth and intensification of agriculture. The semi-arid to arid conditions in such valley bottom areas make them particularly sensitive to climate change owing to the strong dependence of evapotranspiration rates on temperature, and potential shifts in the precipitation amounts and timing. Over the past several years, a series of case studies have been conducted in southern British Columbia, Canada to model potential impacts of future climate change on groundwater recharge and groundwater levels. The study areas represent a range of current hydro-climatic regimes, spanning wet to semi-arid to arid, and focus on alluvial aquifers, situated in mountainous valleys. The same overall methodology and codes were used to assess climate change impacts in each aquifer system. Downscaled climate data from one or more global climate models (GCMs) were used to drive the recharge model. Downscaling was particularly challenging for precipitation due to the inherent difficulty for GCMs to simulate representative precipitation for mountainous regions. Temperature data were generally successfully downscaled. Solar radiation changes were estimated directly from the GCM data. To compensate for difficulties in downscaling, shifts in climate, from present to future-predicted, were applied to the LARS-WG stochastic weather generator to generate daily stochastic weather series for current and future time periods. Direct recharge via precipitation was modeled for each time period using the generated weather series. Spatial recharge was mapped from one-dimensional recharge simulations conducted using the HELP hydrologic model. Indirect recharge from rivers or streams was variably adjusted to account for shifts in timing and/or discharge amount based on future runoff predictions. Groundwater levels for current and future time periods were simulated using MODFLOW. Overall, shifts in direct recharge are generally small, but are highly influenced by selection of downscaling method or GCM, suggesting that prediction of future recharge is highly dependent on the model selected. Thus, when undertaking recharge modelling studies for future climate change, it is important to consider a broader range of models. Shifts in the timing of river discharge proved to have the strongest impact on groundwater levels in one aquifer that is highly connected to this river throughout the valley bottom, thus, consideration of changes in the timing of runoff due to earlier snowmelt, for example, should be explicitly included in models.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H12D..08A
- Keywords:
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- 1218 Mass balance (0762;
- 1223;
- 1631;
- 1836;
- 1843;
- 3010;
- 3322;
- 4532);
- 1829 Groundwater hydrology;
- 1830 Groundwater/surface water interaction;
- 1847 Modeling