fire effects on water
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Fire Effects on Water. September 27, 2006. The Watershed Concept. What is a watershed? Area of land that drains into a common outlet Watershed condition- health or status of a watershed Hydrologic function- receive and process precipitation Support sustained plant growth. - PowerPoint PPT PresentationTRANSCRIPT
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Fire Effects on Water
September 27, 2006
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The Watershed Concept
• What is a watershed?• Area of land that drains into a common
outlet • Watershed condition- health or status of a
watershed– Hydrologic function- receive and process
precipitation– Support sustained plant growth
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Characteristics of a healthy watershed?
• Precipitation infiltrates and percolates into the soil.
• Limited overland flow that causes severe erosion.
• Streamflow response to precipitation is relatively slow.
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Fire effects on watershed condition
• Fire can be a determinant of watershed condition through vegetative change
• Effects of fire on watersheds depends on:– Severity, i.e. plant succession– Extent, Season
• Persistence of watershed conditions depends on the rate of revegetation
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Why is the watershed concept useful when considering the
effects of fire on water?
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Fire effects on the hydrologic cycle
Removal of vegetation and litter effects:• Plant interception • Infiltration rates• Snow accumulation and melting rate• Rates of evapotranspiration• Soil moisture storage• Overland flow (surface runoff)• Streamflow discharge
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Fire Effects on Interception
• Vegetation and SOM on the soil surface intercept the fall of precipitation.
• Fire reduces vegetation canopy and OM accumulation on soil surface.
• Fire decreases interception and increases amount of precipitation reaching the soil surface
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Effects on Snow Accumulation and Melt Patterns
• Snow in higher elevations often a primary source of water to downstream locations.
• Snow accumulates in open spaces with less interception and wind deposition
• Melting rate of snow is more rapid in open spaces than under vegetative canopies.
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How does fire influence infiltration capacities of the soil ?
• Soil organic matter loss• Change in soil structure and reduction in
soil porosity• Direct impact from raindrops• Ash and charcoal residues clog pores
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Evapotranspiration
• ET represents water losses from:– Evaporation from soil, plant, and water surfaces– Transpiration- absorption, movement, and loss of
water through plants.
• ET determines the proportion of precipitation that enters into:– Soil and groundwater– Surface and subsurface runoff
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Effects of Fire on ET• Reduction in vegetation leads to a reduction in
ET losses
• Increases runoff component
• Quantity of overland flow and surface erosion depend on:– Steepness of slope– Soil characteristics– Rainfall severity
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Soil water storage
• Loss of vegetation leads to change in ET losses and more water in subsoil– Surface runoff and stream flow increase
• Soil water over the long term depends on vegetation response.
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Cumulative Effects: Streamflow Response
• Why is there an increase in stream discharge?
• Reduction in interception, infiltration, and ET
• Increase in surface and subsurface runoff
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Impact of fire on water quality
• Changes in physical properties.– Sedimentation and turbidity– Increase in water temperature
• Changes in chemical properties– Nutrient loss in solution vs sedimentation– Organic matter export– Generally short term consequences
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Changes in aquatic habitats
• Increased turbidity effects light penetration and photosynthesis
• Increased temperature alters habitat suitability
• Stream discharge alters stream habitat structure