Abstract
Climatic variability and cumulative forest cover change are the two dominant factors affecting hydrological variability in forested watersheds. Separating the relative effects of each factor on streamflow is gaining increasing attention. This study adds to the body of literature by quantifying the relative contributions of those two drivers to the changes in annual mean flow, low flow, and high flow in a large forested snow dominated watershed, the Deadman River watershed (878 km2) in the Southern Interior of British Columbia, Canada. Over the study period of 1962 to 2012, the cumulative effects of forest disturbance significantly affected the annual mean streamflow. The effects became statistically significant in 1989 at the cumulative forest disturbance level of 12.4% of the watershed area. The modified double mass curve and sensitivity-based methods consistently revealed that forest disturbance and climate variability both increased annual mean streamflow during the disturbance period (1989–2012), with an average increment of 14 mm and 6 mm, respectively. The paired-year approach was used to further investigate the relative contributions to low and high flows. Our analysis showed that low and high flow increased significantly by 19% and 58%, respectively over the disturbance period (p < 0.05). We conclude that forest disturbance and climate variability have significantly increased annual mean flow, low flow and high flow over the last 50 years in a cumulative and additive manner in the Deadman River watershed.
Highlights
Forested watersheds are important sources of streamflow, water regulation and generation for more than 30% of the world’s population [1,2]
The modified double mass curve and sensitivity-based methods consistently revealed that forest disturbance and climate variability both increased annual mean streamflow during the disturbance period (1989–2012), with an average increment of 14 mm and 6 mm, respectively
We conclude that forest disturbance and climate variability have significantly increased annual mean flow, low flow and high flow over the last 50 years in a cumulative and additive manner in the Deadman River watershed
Summary
Forested watersheds are important sources of streamflow, water regulation and generation for more than 30% of the world’s population [1,2]. Changes in forest cover have important effects on the sustainability of water resources, aquatic habitat, and many other ecological functions. In forested watersheds, forest cover change and climate variability are regarded as the two main drivers of hydrological variation [3,4]. The compounding effects of climate variability and land cover change (e.g., forest harvesting, land use conversion) have driven scientific research to focus on how these drivers and their interactions affect the hydrological regime [5,6,7,8,9]. The inability to extrapolate results from the PWE to watersheds of different sizes, topography, climate and land cover types, suggests an important need to Forests 2019, 10, 196; doi:10.3390/f10020196 www.mdpi.com/journal/forests
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