Investigating the effects of forest disturbances on streamflow for mesoscale postglacial catchments using remotely sensed datasets and the case study approach

Abstract:

Changes in forest cover, climate, and their interaction can alter streamflow generation processes. Catchments in the boreal-temperate transition zone, characterized by low relief and widespread surface-groundwater connection, may be especially vulnerable to these factors. Historic understanding of the processes by which forest cover affects streamflow has largely developed in the context of small experimental catchments, many of which are in mountainous regions with bedrock under thin soils. The traditional catchment approach is not practicable for larger catchments (>10 km²) due to several factors, including the importance of regional groundwater and large-scale climate patterns. Further practical difficulties include estimating varying elements of the water budget through space and time, and tracking forest cover change across multiple ownerships. Remotely sensed data products allow for increased investigation of the effects of forest cover change on streamflow at relevant scales. We utilize multiple case studies to quantify how climate and forest cover change affect water yield and peak flows across two spatial orders of magnitude in Minnesota, USA. Case studies include a 650 km² catchment within the Boundary Waters Wilderness in which a fire burned 1/3 of the catchment area, and a large (>8000 km²) catchment in which forest management is active yet dispersed in space. We utilized remotely sensed and processed ET estimates using USGS’ SSEBop data product, climate variables using Oregon State’s PRISM model, and forest disturbance using a Landsat-based data product. Results support a significant effect of forest disturbance on water yield, but no significant effects on peak flows; effects were moderated by catchment storage. Climate signals drove water yield and peak flows at the large basin scale. Persistent error in the water budget derived from estimated precipitation and ET indicates that surface water and regional groundwater can drain distinct spatial areas within larger catchments.