Recent Changes in Climate and Land Use in the Canadian Lake Erie and Lake Ontario Basins: Implications for Runoff and Water Quality

Climate and land-use changes are major drivers of hydrological and water quality dynamics in the Great Lakes Basin. This study investigates recent changes in climate, land use, runoff, and total phosphorus (TP) loading in selected illustrative watersheds within the Canadian Lake Erie Basin and Canadian Lake Ontario Basin during 2009–2022. Results suggest that recent warming and hydroclimatic variability have altered hydrological regimes in southern Ontario, including higher winter temperatures and shifts in seasonal runoff. Land-use changes, including the expansion of row crops and urban areas, have further influenced watershed responses. Variations in TP loading were associated with changes in hydroclimatic conditions and land use. These findings highlight the increasing importance of event-driven nutrient transport under changing hydroclimatic conditions and support adaptive watershed management approaches accounting for seasonal runoff variability and event-driven nutrient transport. This study provides insight into the combined impacts of climate and land-use changes on hydrology and nutrient loading in southern Ontario watersheds. The analysis results enhance understanding of water quality dynamics in the Great Lakes region and support the development of more effective, adaptive, and integrated watershed management strategies under future climate and land-use changes.