Fire Effects on Water. The Watershed Concept What is a watershed? Area of land that drains into a common outlet Watershed condition- health or status.
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Fire Effects on Water
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
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.
Why is the watershed concept useful when considering effects of fire on water?
• Fire can be a determinant of watershed functions through effects on vegetation and soils
• Effects of fire on watersheds depends on:– Severity, i.e. plant succession– Extent, Season
• Persistence of post-fire watershed condition depends on the rate of revegetation
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
Fire 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.
Fire effects on soils: infiltration capacity
• Soil organic matter loss
• Change in soil structure and reduction in soil porosity
• Direct impact from raindrops
• Ash and charcoal residues clog pores
Evapotranspiration: What is it and why is it important
for the H-cycle?• 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
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
Effects of fire on 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.
Cumulative Effects: Effects of Fire on Streamflow Response
• Often fire results in an increase in stream discharge – why?
• Reduction in interception, infiltration, and ET
• Increase in surface and subsurface runoff
Impact of fire on water quality
• Changes in physical properties.
Sedimentation and turbidityIncrease in water temperature
• Changes in chemical properties
Nutrient loss in solution vs sedimentationOrganic matter exportGenerally short term consequences
Changes in aquatic habitats
• Increased turbidity effects light penetration and photosynthesis
• Increased temperature alters habitat suitability
• Stream discharge alters stream habitat structure
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