1. Fire Effects on Water
September 27, 2006

2. 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

3. 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.

4. 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

5. Why is the watershed concept useful when considering the effects of fire on water?

7. 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
What are water repellent soils, where?

8. 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
Then what will happen to interception of precipitation???? Losses.
Increase soil erosion
How infiltration capacities of soils affected by the destruction of OM ????
alters soil structure
Reduce pore space
Increase bulk density
Increase compaction by rain and further losses porosity.
Sealing of surface pores by displace soil particles by rain drops.
Ash and charcoal residues also clogging soil pores.

9. 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.
Snow accumulates in open spaces due to lack of interception.
Snow melts faster in open spaces. Why?????Direct solar radiation

10. 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 S

11. 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

12. 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

13. 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.
Water deficit conditions will recover if vegetative cover recovers soon.

14. Cumulative Effects: Streamflow Response
Why is there an increase in stream discharge?
Reduction in interception, infiltration, and ET
Increase in surface and subsurface runoff

15. 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

16. Changes in aquatic habitats
Increased turbidity effects light penetration and photosynthesis
Increased temperature alters habitat suitability
Stream discharge alters stream habitat structure