Investigation of Coupled Hydrologic and Geochemical Impacts of Wildfire on Southern California Watersheds PDF Download
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Author: Megan Patricia Burke
Publisher:
ISBN:
Category :
Languages : en
Pages : 115
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Book Description
Southern California's fire regime is characterized by periodic large-scale wildfires that occur in late summer and early fall, leaving little time for the landscape to recover before the winter rainy season. Recent trends suggest that fire frequency and intensity is increasing due to factors such as urban encroachment into wildlands and a changing climate. While there is an awareness of the hydrologic consequences of these fires, wildfire's potential effects on water quality in Southern California are less understood, especially at the urban-fringe. This study investigates the impacts of wildfire on regional soils with respect to mercury (Hg) storage, accumulation, and transport potential; on storm runoff chemistry in an urban fringe watershed highly impacted by regional atmospheric pollutants; and on procedures required to model post fire hydrologic response and predict contaminant loading. The regional soil work showed reduced influence of grain size on Hg storage and accelerated accumulation of Hg in burned soil surfaces over time, as well as sediment-facilitated Hg transport in post-fire storms. Analysis of post-fire runoff from an urban fringe watershed showed up to three orders of magnitude increases from pre-fire levels in the concentrations and loads of many trace metals, including cadmium (Cd) and lead (Pb). These results also highlighted a shift in the timing of chemical delivery in post-fire storms to coincide with, rather than precede, peak discharge, amplifying the fire's impacts on mass loading. The investigation into modeling these impacts allowed for initial estimates to be made of seasonal loading, the development of a model to simulate pre-fire hydrology, and an identification of steps required to develop a model application capable of simulating post-fire sediment and metal concentrations. The resultant body of work provides an increased understanding of wildfire's effects on Southern California's soils and water and on what is required to predict these impacts.
Author: Megan Patricia Burke
Publisher:
ISBN:
Category :
Languages : en
Pages : 115
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Book Description
Southern California's fire regime is characterized by periodic large-scale wildfires that occur in late summer and early fall, leaving little time for the landscape to recover before the winter rainy season. Recent trends suggest that fire frequency and intensity is increasing due to factors such as urban encroachment into wildlands and a changing climate. While there is an awareness of the hydrologic consequences of these fires, wildfire's potential effects on water quality in Southern California are less understood, especially at the urban-fringe. This study investigates the impacts of wildfire on regional soils with respect to mercury (Hg) storage, accumulation, and transport potential; on storm runoff chemistry in an urban fringe watershed highly impacted by regional atmospheric pollutants; and on procedures required to model post fire hydrologic response and predict contaminant loading. The regional soil work showed reduced influence of grain size on Hg storage and accelerated accumulation of Hg in burned soil surfaces over time, as well as sediment-facilitated Hg transport in post-fire storms. Analysis of post-fire runoff from an urban fringe watershed showed up to three orders of magnitude increases from pre-fire levels in the concentrations and loads of many trace metals, including cadmium (Cd) and lead (Pb). These results also highlighted a shift in the timing of chemical delivery in post-fire storms to coincide with, rather than precede, peak discharge, amplifying the fire's impacts on mass loading. The investigation into modeling these impacts allowed for initial estimates to be made of seasonal loading, the development of a model to simulate pre-fire hydrology, and an identification of steps required to develop a model application capable of simulating post-fire sediment and metal concentrations. The resultant body of work provides an increased understanding of wildfire's effects on Southern California's soils and water and on what is required to predict these impacts.
Author: Isabel Escobar-Sanchez
Publisher:
ISBN:
Category : Civil engineering
Languages : en
Pages : 0
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Wildfire impacts include loss of vegetation, water repellent soil layer, and subsequent flooding after the first major rain event. Post-fire flooding is a growing issue that requires a better understanding of post-fire hydrological changes. This research uses ParFlow-Common Land Model (ParFlow-CLM), a parallel, integrated surface, and subsurface hydrologic model, to simulate post-fire hydrologic conditions and recovery. We developed a hillslope-scale model of the 2003 Old Fire in Devil Canyon, California, for a 500 m x 1000 m lateral extent. The subsurface reaches 12.4 m and is assigned a variable cell thickness. This allowed an explicit consideration of burn severity and the development of hydrophobic layers within the upper 4 cm. Hydrophobic layers included a non-homogenous reduction in porosity and permeability. Evapotranspiration was simulated by reducing post-fire leaf area index (LAI), where scenarios considering an extreme loss of vegetation involved using grass and dirt land use classifications. No burn, medium burn, and high burn severity were simulated for four pre-fire land use classifications amounting to 44 post-fire scenarios. Simulation results showed evapotranspiration decreased from 19% to 54% and mean runoff increased from 10% to 70%. Bare soil or dirt represented the complete loss of vegetation, which produced the maximum runoff and substantially increased surface storage (conversely decreasing subsurface storage). The product of this work is a gridded percent change in subsurface storage, runoff, evapotranspiration and surface storage due to varying degrees of burn severity and vegetational removal. This research demonstrates the novel parameterization of a hydrologic model that simulates coupled surface and subsurface hydrologic processes, which can be used to provide guidance for post-fire watershed management.
Author: Ravleen Kaur G. Khalsa-Basra
Publisher:
ISBN:
Category : Fluvial geomorphology
Languages : en
Pages : 127
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Book Description
Rivers in semi-arid climates are directly influenced by local geographic and hydrologic conditions and impacted by modifications to hydrology via urbanization. Changes can influence erosion, morphology, habitat sustainability, and watershed health. In highly urbanized southern California coastal regions, these rare open spaces provide vital ecosystem services. Los Peñasquitos Creek in San Diego County is one such watershed. Using stream surveying and laboratory methods we quantified channel characteristics, grain size distribution, total metal concentration [M], organic carbon (%OC), and phosphate to longitudinally characterize the creek for improved management. Results identified three distinct reaches in the watershed (upper, middle, lower). Downstream, depth and velocity are inversely related (R2: -0.86), while grain size decreases (D50:45mm-0.2mm), influenced by slope-driven widening and overbank deposition in the middle reach. Phosphate and [M] vary, likely influenced by anthropogenic runoff. Data suggests that %OC (instead of grain size) is more strongly correlated with [M] overall, especially zinc and lead, and is influenced by riparian zone vegetation density. This study emphasizes the importance of local and geomorphic influences on geochemical variability. Suggestions include 5-year or drought year Cu, Hg, Pb, Zn monitoring (exceeded SQuirT screening) at specific sites and continued nutrient analysis for eutrophication at the confluence. Coastal watersheds in semi-arid climates are influenced by hydrologic variation from sedimentation, urbanization, and climate change. Southern California watersheds are unique in their small spatial-scale and are vulnerable to flooding from increased frequencies and intensities of short-duration heavy rainfalls and cyclic drought-storm patterns in the semi-arid climate. Runoff is exacerbated with population growth and land-cover change. This study also uses two methods to estimate and model runoff in future scenarios using HEC-RAS. The first method estimates recurrence intervals (RI) based on local PeakFQ data. Commonly used in hydraulic engineering and flood modeling, the RI method estimates flows as an average number of times a peak flow will occur over a return period (years). For Los Peñasquitos watershed, the estimated flows for the RI years shown are as follows: RI-5=2,899, RI-10=4,095, RI-25=5,675, RI-50=6,870, RI-100=8,066, RI-500=10,841 cfs. To address the impact on flow from precipitation and soil saturation, the second method uses a 5-day Antecedent Precipitation Index (API) and daily precipitation in a multiple regression empirical model to estimate runoff. Future projections for rainfall, based on climate models using Representative Concentration Pathways (RCP) are applied to observed data and interpolated to RCP 2.6, 4.5, 6.0, and 8.5 scenarios and resulted in 7,908-8,246 cfs within the next 50-100 years. We recommend using future projections for rainfall and land-use to better estimate flow and address projected trends.
Author: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309499879
Category : Science
Languages : en
Pages : 161
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Book Description
California and other wildfire-prone western states have experienced a substantial increase in the number and intensity of wildfires in recent years. Wildlands and climate experts expect these trends to continue and quite likely to worsen in coming years. Wildfires and other disasters can be particularly devastating for vulnerable communities. Members of these communities tend to experience worse health outcomes from disasters, have fewer resources for responding and rebuilding, and receive less assistance from state, local, and federal agencies. Because burning wood releases particulate matter and other toxicants, the health effects of wildfires extend well beyond burns. In addition, deposition of toxicants in soil and water can result in chronic as well as acute exposures. On June 4-5, 2019, four different entities within the National Academies of Sciences, Engineering, and Medicine held a workshop titled Implications of the California Wildfires for Health, Communities, and Preparedness at the Betty Irene Moore School of Nursing at the University of California, Davis. The workshop explored the population health, environmental health, emergency preparedness, and health equity consequences of increasingly strong and numerous wildfires, particularly in California. This publication is a summary of the presentations and discussion of the workshop.
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.
Author: P. B. Rowe
Publisher:
ISBN:
Category : Erosion
Languages : en
Pages : 98
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Author:
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 46
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Semi-arid urban coastal streams are at an increased risk of future fire disturbances due to climate change and anthropogenic activity. These disturbances can impact ecosystem services such as rainfall-runoff processes and the transportation of soil-bound contaminants. Soil moisture content and infiltration are important antecedent hydrologic conditions for rainfall-runoff processes that can influence the transport and storage of toxic heavy metals like mercury (Hg). Inorganic mercury can be converted into a potent neurotoxin, methylmercury (MeHg), and mobilized to coastal waterways through runoff and erosion. This thesis analyzed soil moisture content, infiltration, and soil Hg concentration (total mercury (THg) and MeHg) in a perennial semi-arid urban stream channel in Southern California. In June 2018, a 38-acre fire burned a portion of the riparian zone in Alvarado Creek, a tributary of the San Diego River in California, United States. Three transects (two unburned and one burned) were monitored monthly to the evaluate the complex spatial and temporal dynamics of soil moisture and infiltration patterns. Multiple soil samples across all three transects were obtained to investigate the consequences of fire for the transport and storage of THg and MeHg concentrations. Average dry season soil moisture content was less than 5 percent volume water content (%VWC) for all transects, and the burned transect exhibited the lowest %VWC during the wet season. Infiltration rates displayed a high degree of spatial and temporal variability, however the location with the highest burn severity had the lowest average infiltration rate. THg concentrations ranged from 10.63 ng/g to 182.38 ng/g, and MeHg concentrations ranged from 0.03 ng/g to 1.58 ng/g. THg and MeHg concentrations increased at all transects after the first significant post-fire precipitation event of the wet season, and the largest increase was displayed at the downstream locations of the burned area. This thesis demonstrated the differences of hydrologic properties and terrestrial Hg contamination among burned and unburned transects in a fire disturbed semi-arid urban stream channel. The research improves the characterization of post-fire hydrologic conditions for rainfall-runoff processes and provides the first high resolution mercury soil analysis of an urban fire disturbed stream in Southern California.
Author: Vijay P. Singh
Publisher: Allied Publishers
ISBN: 9788177645477
Category : Groundwater
Languages : en
Pages : 588
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Author: Phelicia Marie Gomes
Publisher:
ISBN:
Category : Fire ecology
Languages : en
Pages : 250
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Author: Markus Berli
Publisher:
ISBN:
Category : Soils
Languages : en
Pages : 42
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"The goal of this study was to provide an overview of how wildfires affect watershed hydrology; review current approaches to quantify wildfire effects on watershed hydrology geared towards solving watershed hydraulic engineering problems like flooding, erosion, sediment and debris yield as well as landslides; analyze available data on the persistence of wildfire effects on soil hydrologic properties as a basis to derive a wildfire effect recovery function; and identify current gaps of knowledge and outline how to fill them within upcoming research efforts"--P. iii.
