Assessing the impacts of climate change on fluvial processes: using a physically-based model to determine hydrologic responses of the Slate River
Abstract
Watershed models are an important tool in regional planning and
conservation efforts. They can provide valuable insight into the potential impacts
of different land use changes and future climate change scenarios on water
resources, which can lead to better, more informed decision making. Climate
impacts, in particular, add a new level of uncertainty with regard to freshwater
supplies as the hydrological cycle is intimately linked with changes in
atmospheric temperatures. The main objective of this study is to investigate the
extent of long-term climate change on streamflow and stream temperature within
an agriculturally defined watershed in Northern Ontario. For this purpose, the Soil
and Water Assessment Tool (SWAT) model was utilized to provide a better
understanding of how hydrological processes in the Slate River Watershed will
alter in response to long-term climate change scenarios. The SWAT model is a
distributed/semi-distributed physically-based continuous model, developed by the
USDA for the management of agricultural watersheds, and is currently one of the
most popular watershed-based models used in climate change analysis of snowmelt
dominated watersheds. Historic flow data was compared to a discharge
model that reflected four climate models driven by SRES A1B and A2 through
the middle and end of the century. Hydrology modelling was enhanced with
stream temperature analysis to gain a comprehensive understanding of the
extent of changing climate regimes on the Slate River. A linear regression
approach representing a positive relationship between stream temperature and
air temperature was used to determine the thermal classification of the Slate
River. Our results indicated that the Slate River was well within the warm-water
character regime. Unusual high stream temperatures were recorded at mid-
August; these were accompanied by low water levels and a lack of riparian
vegetative cover at the recording site, providing a possible explanation for such
temperature anomalies. The results of the flow discharge modelling supported
our hypothesis that tributaries within our ecosystem would experience increasing
water stress in a warming climate as the average total discharge from the Slate
River decreased in both climate scenarios at the middle and end of the century.
Although the lack of accurate subsurface soil data within the study region
prevented our discharge model from quantifying the changes in stream
discharge, the strong correlation between the observed and simulated flow data
as reflected by a 0.92 r² statistic gave us confidence that discharge from the
Slate River will continue to follow a decreasing trend as climate change persists
into the future. This study aims to support the future endeavours of hydrologic
modelling of watersheds in Northern Ontario by illustrating the current capabilities
and limits of climate change analysis studies within this region.