Regional disparities in water availability and low flow conditions in rivers across Canada

Abstract

Water resources play an important role in many aspects of our daily lives, e.g. industrial food processing, irrigation, and hydropower generation, etc. The natural flow regime and water availability were studied across Canada using 167 catchments from the Water Survey of Canada dataset (Reference Hydrometric Basin Network - RHBN). We established a systematic analysis of water availability (annual and monthly runoff) to determine both the quantity and distribution of water within the year. In each province, we investigated the severity of low flow conditions namely the magnitude, seasonality, and duration of extreme low flows. There are prominent disparities in water availability at the annual and monthly time scales across Canada. The annual runoff characteristics showed a relatively abundant quantities of water on the east and west coasts (800-2300 mm/year). Annual runoff is critically low (<150 mm/year) in the prairies and northern territories. Monthly analyses revealed eminent differences in the timing and magnitude of high and low flows. The spring snowmelt is the main trigger of high flows in most provinces. However, the quantities of water during freshet period varied dramatically across provinces. British Columbia showed among the highest hydrological variability where some catchments showed relatively high flows year around. In Canada, a second high flow period was observed in some provinces (e.g., Quebec, Ontario, and the Maritimes). The underpinning hydrological processes and the precipitation regime are discussed to explain the regional hydrologic disparities. The monthly flow of the 80th percentile (Q80; monthly flow duration curve) was used as the cutoff to describe low flows both in terms of magnitude and duration. The Q80 variability across Canadian rivers was significantly large (0.3-100 mm/month). Many regions have one period of extreme low flows except in Newfoundland, New Brunswick, British Columbia, Ontario, Quebec and Saskatchewan where 2 seasons of low flows can be observed. In Newfoundland and New Brunswick the low flow period was the shortest (2.6 months). In contrast, in the prairies and north territories, the low flow period extended between 3.4 and 4 months. We further explained the disparities in water availability and low flows from analysis of the daily flow duration curve (FDC). We quantified the differences in the flow response from flow indices calculated from FDC (baseflow index, low flow index, and slope of the FDC). The results of water availability and low flows have important socio-economic impacts on water supply, reservoir operations, and far-reaching implications on the health of aquatic habitats.