ASSESSING HYDROLOGIC IMPACTS OF THE 2013 RIM FIRE ON THE TUOLUMNE RIVER WATERSHED IN CENTRAL VALLEY, CALIFORNIA PDF Download

Author: Cole Blasko
Publisher:
ISBN:
Category : Hydrological surveys
Languages : en
Pages : 193

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Book Description
Understanding how wildfires affect watershed hydrology is a vital aspect in the protection of water resources and mitigation of flooding risks in fire-prone regions. The 2013 Rim Fire, for example, burned ~21.5% of the Tuolumne River Watershed that supplies San Francisco, California, USA with 85% and 17% of its water and electricity, respectively. The goal of this study was to develop Soil and Water Assessment Tool (SWAT) models to evaluate and better understand the impacts of the 2013 fire on the hydrology of the Tuolumne Watershed. Two SWAT models were developed, with Model 1 based on pre-fire, 2011 land cover data and Model 2 based on post-fire, 2016 land cover data. After calibration, both models performed well in daily discharge estimation, yielding R2 and Nash-Sutcliffe Efficiency (NSE) values ranging from 0.69-0.98 and 0.60-0.98, respectively when comparing to discharges observed at three United States Geological Survey (USGS) gaging stations. Our modeling results from two burned sub-basins show the Rim Fire could drastically increase the magnitude of peak flows, potentially leading to severer flooding events and damages. Our results also show fire-induced increase in surface runoff, with 90, 84, and 124% estimated for sub-basins burned at low, moderate, and high severity, respectively. Fire's impact on base flow, however, seemed negligible. Our water-budget analysis and cross-model comparison, furthermore, indicate necessity to account for fire-induced land condition changes while developing watershed hydrologic models. Across the entire Tuolumne watershed, it is estimated that evapotranspiration rates decreased by 27%, lateral flow increased by 64%, and return flow decreased by 28% due to the fire. Within burned areas of the watershed, an average higher discharge of 139 mega m3 yr-1, flashier response to precipitation events, a maximum of 45% more surface runoff (2017), and a total of 2 m less evapotranspiration were calculated during the post-fire period, i.e., 2013-2018. The modeling approaches and results from this study will help land managers better predict flooding, prioritize funds and mitigation efforts, and model the effects of wildfire over a large spatial and temporal scale through incorporation of readily available data that can be implemented quickly after a wildfire occurs.