| Citation |
Markus Weiler, Cornelia Scheffler, Art Tautz, and Klemens Rosin (2009) Development of a Hydrologic Process Model for Mountain Pine Beetle affected Areas in British Columbia, University of British Columbia, University of Freiburg, UBC Fisheries Centre. |
| Abstract/Description or Keywords |
The infestation of the Mountain Pine Beetle (MPB) has turned into a major threat to the natural habitat of British Columbia. Pine forests have been decimated in the last five years by the mountain pine beetle (MPB) (Dendroctonus ponderosae Hopk.). This infestation has impacted more than 9 million ha of pine forest in BC and models predict that by 2015, 76% of the pine forest will be dead or dying [BC Ministry of Forest and Range 2008]. A large proportion of British Columbia’s pine forests occur in the Fraser River Basin, which is recognized worldwide as a watershed rich in both natural resources and cultural diversity. Within the basin, water forms a critical link between the basin and its inhabitants, whether in the form of water for fish, riparian corridors for biodiversity , reserves for drinking water or water licenses for irrigation or hydro generation . Because of these tight associations, changes to the hydrological cycle will significantly change the character and viability of many aspects of life within the basin. Especially, forest cover is a key modifier of the watershed’s peak flow regime. The peak flow generally increases when forest cover is reduced due to natural and/or man made disturbances. To determine those peak flow increases we developed and applied a hydrological model. Since some regions of the Fraser Basin have only a limited number of gauging stations (or are even ungauged), the goal was to develop a model that does not rely on complex data inputs for its validation and calibration . The model consists of an input component, a runoff generation component, a land cover modification module and a stream routing module. The input component determines the mean annual snowmelt and maximum rainfall based on climatic data. The climate input will be modified in the land cover modification module in relation to the simulated vegetation cover. The derived information is then used to determine the time and the capacity of the peak flow for every 3rd order watershed. The runoff generation component delineates the hydrologic processes such as Hortonain Overland Flow, Saturation Overland Flow and Shallow Surface Flow. This delineation is based on factors such as topography, slope, aspect, wetness index, drainage pattern and drainage density. Combining those components, the model computes a map of peak flow contribution that is used to assess sensitive areas for peak flow production. Depending on the respective spatial scale, the derived peak flow information will be used in the stream routing module to account for cumulative effects. In this report, we modeled the impact of pine coverage in grey stand as well as pine cover harvested for the Fraser Basin. The simulated results were compared to the baseline scenario, a scenario assuming no Mountain Pine Beetle activity. Our modeling results are summarized as follows: The reduction in active pine cover or the removal of forest cover results in an increase of peak flow whereas 1. Equal area reductions in vegetation do not lead to the same peak flow increases and suggests the existence of scale effects 2. The degree of peak flow increases due to land use changes has a clear relationship to watershed size. Peak flow increases between 23% and 88% have a higher probability at higher watershed scale. 3. Harvesting activities have a greater impact on peak flows than does grey attack; similar findings were published by the Forest Practice Board [2007]. |
