Assessing the impact of future land-use changes on hydrological processes in the Elbow River watershed in southern Alberta, Canada

The Elbow River in southern Alberta, Canada is the source of the Glenmore reservoir, which provides drinking water to the City of Calgary. Due to the rapid population growth in Calgary, the Elbow River watershed (ERW) that covers about 1238 km2 has been under considerable pressure for land-use development over the last decade. This study was undertaken to assess the impact of potential land-use changes over the next 20 years on the hydrological processes in ERW by combining a land-use cellular automata (CA) model and the distributed physically-based MIKE-SHE/MIKE-11 hydrological model. The CA model was calibrated using four land-use maps covering the period 1985–2001 and validated against the maps of 2006 and 2010. Simulations of land-use changes were then performed from 2006 to 2031 at a five year interval; land-use based parameters were extracted from the simulated maps and transferred to MIKE-SHE/MIKE-11. MIKE-SHE was calibrated for the period 1985–1990 and validated for the period 2000–2005. The Nash and Sutcliffe coefficients of efficiency calculated between observed and simulated flow data for the calibration and validation periods are 0.56, 0.52, 0.79, and 0.75 based on different hydrometric stations respectively, indicating an acceptable level of performance of the model. Land-use changes analyzed for the period 2001–2031 reveal a 65% increase in built-up areas, 20% in rangeland/parkland, and 1% in agriculture along with a reduction of 28% in deciduous, and 6% in evergreen forest. As a result, the hydrological modeling indicates an increase of 7.3% in overland flow, and a decrease of 1%, 13.2%, and 2.3% in total evapotranspiration, baseflow, and infiltration respectively along with a decrease of the total flow by 4%. These results reveal a potential significant negative impact on the sustainability of ground/surface water supplies and groundwater storages in the future in the watershed in addition to an increased risk of flashy floods. The study also revealed that due to the complex hydrological regime existing in the study area, a comprehensive physically-based method is required to better represent the interaction between groundwater and surface water. The combined CA/MIKE-SHE models appear as a useful tool to assess the impact of land-use changes on the hydrologic cycle and to better understand the connection among the hydrologic components in the Elbow River watershed.