Quantifying the individual and combined influence of climate change, land cover transition, and internal climate variability on the hydrology of a snow-dominated forested watershed

The interplay between climate dynamics, land cover transformations, and hydrologic processes is critical for predicting watershed responses in a changing environment. In this study, we assess the impacts of climate and land cover changes on the hydrology of the Batchawana River, a forested watershed in central Ontario, under global temperature increases of 1.5–4°C. We examine the roles of external forcings and natural climate variability in historical and future regional hydrologic changes. The analyses are based on eight downscaled General Circulation Models (GCMs) that participated in CMIP5, the Canadian Regional Climate Model Large Ensemble (CanRCM4-LE), and its two bias-adjusted variants. A semi-distributed hydrological model, within the Raven hydrological framework, is calibrated and driven by GCMs/RCMs to analyze future snow and runoff characteristics. Two land cover scenarios are simulated to assess their combined impact with climate change on watershed response. Results show a projected decline in snowpack, indicating a potential shift from a nival to a nival-pluvial hydrological regime in a warmer climate. Mean annual streamflow is expected to increase while the annual maximum flow and 7-day low flow are projected to decline. Shifts from coniferous to deciduous forests have minimal impacts on streamflow, but vegetation loss substantially alters its dynamics particularly for annual mean and low flow. As warming intensifies, the influence of external forcings becomes more pronounced in driving changes to streamflow and snowpack.