Abstract
Climate change and rapid urbanization could possibly increase the vulnerability of the Great Lakes Basin, Canada, which is the largest surface freshwater system in the world. This study explores the joint impact of climate change and land-use changes on the hydrology of a rapidly urbanizing Credit River watershed which lets out into Lake Ontario 25 km southwest of downtown Toronto, Ontario (ON), Canada; we began by classifying the watershed into urban and rural sections. A non-parametric Mann–Kendall test and the Sen slope estimator served to detect and describe the annual-, seasonal-, and monthly-scale trends in the climate variables (temperature, precipitation, and evapotranspiration), as well as the streamflow characteristics (median annual streamflow, baseflow, Runoff Coefficients (RC), Flow Duration Curve (FDC), Center of Volume (COV), and Peak Over Threshold (POT)) since 1916 for four rural and urban sub-watersheds. The temperature, precipitation and evapotranspiration (1950–2019) showed significant increasing trends for different months and seasons. Furthermore, the results indicated that the median annual streamflow, 7-day annual minimum flow, and days above normal are increasing; meanwhile, the annual maximum streamflow is decreasing. A total of 230 datasets were tested for their trends; of these, 80% and 20% increasing and decreasing trends were obtained, respectively. Of the total, significant trends (<0.05%) of 32% and 2% increasing and decreasing, respectively, were observed. The results of the FDC analysis indicated a decline in the annual and winter 10:90 exceedance ratio over the years for the rural and urban sub-watershed gauges. The BFI results show that the BFI of the rural areas was, on average, 18% higher than that of the urban areas. In addition, the RC also showed the influence of land-use and population changes on the watershed hydrology, as the RC for the urban gauge area was 19.3% higher than that for the rural area gauge. However, the difference in the RC was the lowest (5.8%) in the summer. Overall, the findings from this study highlight the annual, seasonal, and monthly changes in the temperature, precipitation, evapotranspiration, and streamflow in the watershed under study. Based on the available monitored data, it was difficult to quantify the changes in the streamflow over the decade which were attributable to population growth and land-cover use and management changes due to municipal official planning in the watershed.
Highlights
The mean global and mean Canadian temperature rose by 0.8 ◦C and 1.7 ◦C, respectively, between 1948 and 2016 (3.3 ◦C, 1.7 ◦C, 1.5 ◦C, and 1.7 ◦C for the winter, spring, summer, and fall seasons, for Canada, respectively), which is a cause for concern [1]
The hydrology of the Great Lakes Basin is affected by land cover and land-use changes arising from the watershed’s development, including a rise in population of 37 to 105 million from 1990 to 2015 [5]
The Environmental Law and Policy Center, in concert with the Chicago Council on Global Affairs, delivered a report on climate change’s influence on the Great Lakes, wherein they highlighted for policymakers the vital importance of acting to protect our natural resources [7]
Summary
The mean global and mean Canadian temperature rose by 0.8 ◦C and 1.7 ◦C, respectively, between 1948 and 2016 (3.3 ◦C, 1.7 ◦C, 1.5 ◦C, and 1.7 ◦C for the winter, spring, summer, and fall seasons, for Canada, respectively), which is a cause for concern [1]. Drawing upon discharges recorded between 1980 and 2000, the temporal effect of rapid urban construction on the streamflow in a 100-year floodplain in Texas was studied [24] They found a statistically significant increasing trend between the instantaneous peak flow and the area rendered impervious through urbanization. In the present study, annual and seasonal changes in streamflow, together with precipitation, temperature, evapotranspiration, readily available land cover, land use, and population density information were investigated, in order to shed light on the research question: “Has streamflow changed?” the present study’s primary objective was to examine trends in the historic streamflow and identify the impact of climate change and/or urbanization through different statistical and analytical approaches for a rapidly urbanizing Credit River watershed in the Ontario (ON) portion of the Great Lake Basin
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