Theme 7-2-Base flow analysis – A tool in assessing climate change impacts on groundwater resources.

Abstract

As the time scales for various hydrologic components differ by orders of magnitude, it becomes difficult to study the impact of climate change scenarios at local and regional levels. A heuristic method is developed to link hydrologic components to assess impacts related to climate variability by focusing on a large river system in south-central Ontario, Canada. Time series of hydrologic and climatic data for 78 sub-watersheds and 12 climate stations within and surrounding the Grand River watershed in Ontario are employed to characterize the region in terms of base flow index and excess precipitation. Base flow index (defined as base flow relative to total stream flow) varies from 20 percent in areas with extensive deposits of fine textured glaciolacustrine sediments to greater than 80 percent in areas where coarse granular sediments and bedrock occur at the ground surface. Excess precipitation (defined as stream flow relative to precipitation) is greatest during January and February at 90 percent and least during July and August at 10 percent. When plotted as a function of temperature, excess precipitation displays definite hysteresis and is greater during the spring than during the fall, presumably due to antecedent moisture conditions. Combined, these results provide a rational basis for estimating rates of groundwater recharge subject to current climatic conditions and climate change. The importance of contiguous data for various hydrologic components is demonstrated by focusing on information windows with concurrent data sets.