Fire Effects on Water

1. Fire Effects on Water

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. 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

6. 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

7. 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.

8. 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

9. 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

10. 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

11. 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.

12. 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

13. 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

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