IWRA Proceedings

Groundwater is an essential resource for agricultural production including activities such as irrigation and livestock watering. Climate change, agricultural intensification, and population growth driving urban expansion create pressures on rural water supplies. Conflicts arise surrounding competing uses when there is not enough water available. Predictive models are necessary to examine the future water balance, including impacts of climate and land use change, to ensure collective uses do not have adverse impacts.

The objective was to examine future groundwater availability at the subwatershed scale for water-stressed areas dominated by agricultural use. This was carried out using a research site surrounding the lower portion of Whitemans Creek (LWC), an affluent of the Grand River in southern Ontario, Canada. The analysis of the subwatershed water balance included collection of hydrological field data and numerical simulations using SWAT-MODFLOW. Past water deficits (P-PET<0) have been observed for several years and current permitted pumping is similar in magnitude to the average past recharge estimate. Water deficits could pose conflicts for future water takings or increased irrigation needed for adaptation. However, the allowed water takings appear to be much higher than the declared values. Actual water takings need to be more precisely determined.

The predictive modelling results indicate that there will be more recharge, higher baseflow and higher groundwater levels in the study subwatershed during future (2041-2070) winter and fall seasons. However, there will also be less water available during critical crop periods (lower recharge and baseflow in spring and summer). Changes in timing of water availability may impact agricultural practices, such as a need for more irrigation during the growing season.

Overall, the analysis of past and potential future hydrological conditions indicates that the LWC groundwater system appears to be fairly resilient to climate change. Possible future increased water availability can provide several opportunities for agricultural production. However, since the study subcatchment is already stressed, some challenges may occur. Small subwatersheds such as the LWC, with highly permeable soils, stresses on current water availability and dense agricultural activities, can be vulnerable to changes in the water balance.

Long-term monitoring of all components of the water balance is critical in high water use watersheds to build long-term datasets that can support integrated water management. Publically-funded programs, such as Ontario’s Provincial Groundwater Monitoring Network and Water Survey of Canada's real-time hydrometric data, are of critical importance to examine impacts of climate change on rural water supply.