Catchment streamflow response to climate change conditioned by historic alterations of land-use: forest harvest, succession, and stand conversion.

Abstract:

Headwater streams provide drinking water for millions of people and serve a significant nexus, contributing to the physical, chemical, and biological integrity of navigable waters. Long-term research sites, such as the Fernow Experimental Forest serve as the regions bellwether for ecological change. Nevertheless, few studies have quantified the long term impacts of forest treatment and climate change on streamflow for the catchments of the Fernow. This study serves this roll by accessing the change in water and energy balance of four catchments (WS-1, WS-4, WS-6, WS-7) subject to forest harvest, natural and suppressed regrowth, and stand conversion. We apply the Budyko framework to quantify the relative contributions of climate and land cover changes on annual streamflow between two time periods and over a five year interval spanning 1951-2011. Based on this analysis land-use, forest succession, and climate change-variability are differentially impacting streamflow. In the two-period analysis climate change is responsible for on average 3 % change in mean annual runoff (MAR). Forest harvest and/or succession caused changes in MAR of -0.8 % to -30.0 %. The Budyko decomposition method applied over five year intervals captured the influence of forest treatment on streamflow well. However, the reference (WS-4) is changing in ways that climate alone cannot describe. Overall, it is important to consider how climate, land-use disturbance, and forest succession corroborate by distinguishing their respective impacts.