Hydrologic Impacts of Afforestation in Coldstream Creek, Canada
This project examines how land use change influences watershed hydrology in Coldstream Creek, Canada. Using the RHESSys model, streamflow is simulated under two scenarios: a baseline landscape and an alternative where all lawn areas are converted to young forest. Streamflow outputs are compared across time (1971–1996) and space to assess changes in flow magnitude, frequency, and spatial distribution. The analysis evaluates how afforestation alters peak flow events and hydrological patterns at the hillslope scale, highlighting how small land use changes can impact broader watershed processes.
1) How does converting lawn areas to young forest affect streamflow patterns over time?
2) Does afforestation increase or decrease the magnitude and frequency of peak flow events?
3) How do hydrological changes vary spatially across the watershed at the hillslope scale?
4) Do areas without direct land use change experience hydrological impacts?
Hydrological processes were modeled using the RHESSys system with spatial data including DEMs, land use, soil, and vegetation layers. Two scenarios were simulated: a baseline land use scenario and an alternative scenario in which all lawn areas were converted to young forest. Model outputs were analyzed at basin and hillslope scales from 1971 to 1996.
Land use within the watershed is dominated by young forest, while cropland is concentrated across the central corridor and smaller areas of rangeland, lawn, and old forest are distributed throughout the basin (Fig. 1). Afforestation has altered streamflow patterns across the watershed. In the alternative scenario, all lawn areas were converted to young forest to evaluate how localized land use change influences watershed hydrology (Fig. 2). Converting lawns to young forest led to increased streamflow in some years and locations, the creation of new peak flow events, and a reduction in the intensity of some existing peaks in streamflow. Spatially, the largest increases in streamflow occurred in central areas with mixed land use (lawns, cropland, rangeland), while changes also extended beyond the converted areas.
The proposed alternative scenario is to convert all lawn area into young forest (Fig. 2).
The natural run exhibited episodic peak flow events throughout the study period, with major peaks occurring in the mid-1970s, mid-1980s, and mid-1990s (Fig. 3).
Under the afforestation scenario, streamflow magnitude changed across multiple years, with some peak flow events increasing while others decreased relative to the natural run. Additional peak flow events emerged in the mid-1990s, while several existing peaks showed reduced flow magnitude (Fig. 4).
Spatial differences in streamflow were concentrated primarily within the central watershed, where lawn, cropland, and rangeland land uses were most prevalent (Fig. 5, 6). The alternative afforestation scenario produced localized increases in streamflow magnitude that extended beyond the directly converted areas, indicating interconnected hydrological responses across the basin (Fig. 7).
Even relatively small land use changes (~2.6% of the watershed area) produced measurable hydrological effects. Increased vegetation likely enhanced evapotranspiration and soil moisture retention, altering runoff dynamics and streamflow behavior across the basin. These findings demonstrate how localized land cover modifications can influence broader watershed-scale hydrological processes.
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