DETERMINING THE IMPACTS OF WILDFIRES ON PEAK FLOOD FLOWS IN HIGH MOUNTAIN WATERSHEDS

摘要

Mountainous forested regions are the major sources of water for meeting downstream water demands in many parts of the world, including the United States, where two-thirds of the freshwater supply is estimated to originate from these areas. Wildfires pose significant threats to downstream urban infrastructure and livelihoods by impacting the timing, quantity and quality of waters emerging from these forested ecosystems. Wildfires affect key processes of the water cycle by reducing infiltration and in- terception, resulting in higher runoff volumes. Predicting post-fire flood events is important for proper water management and planning, including the safety of downstream communities. The objective of the study is to determine how changes in the locations of wildfire events coupled with the type (severity) of fire events affect peak flow regimes of high mountain watersheds. American Fork, a high mountain forest watershed in Utah with an area of 60 sq. miles (155 sq. km) and elevations ranging from 5,000 ft. to 11,700 ft. (1550 m to 3600 m), is taken as the study area. A historical fire event that took place in a neighbouring watershed was superimposed on three different locations of the studying watershed with varying severity. A hydrologic model named Distributed Hydrologic Soil Vegetation Model was used to predict the flows due to changes in land cover and hydrologic processes for different wildfire events. Changes in peak flow due to different wildfire events at different locations of the watershed are analysed to estimate how location and type of wildfire events affect the peak flow regimes of the watershed and how thus it affects the overall downstream water supply. This study also identifies the critical location in the watershed for which the peak flow regime of the watershed will be most vulnerable due to a certain extent of wildfire.