Climatic variability, land-cover change, and forest hydrology in the Pacific NorthwestDavid W. PetersonJISAO Climate Impacts GroupForest Hydrology

Current Research:Climate – Water – Forest

Interactions

Climate

Water Forests

Water and ecosystem productivity

Annual Outflow Gross photosynthesis

Numeric Terradynamics Simulation GroupUniversity of Montana

Forest dependence on water resources in the PNW

Trees require water for photosynthesis and growthSummer water deficits limit forest productivity Total precipitation Seasonality of precipitation

At high elevations, excessive snowpack limits growing season length and forest productivityWater availability influences forest species composition and density

Forest influences on water resources

Forests influence water resources by… Intercepting precipitation Influencing infiltration and runoff rates Modifying soil water-holding capacity Extracting soil water to meet

transpiration requirements Influencing snowpack accumulation

and melt rates

Water and ecosystem productivity

Annual Outflow Gross photosynthesis

Numeric Terradynamics Simulation GroupUniversity of Montana

Land-cover changes

Disturbances (variable intensity) Forest harvesting Wildfires Insects and diseases Land conversions

Forest growth and development Forest structure Leaf area Species composition

Climate change

Climatic variability and change

Annual climatic variability and ENSO Affect forest stress levels Extreme events can disturb forests

Decadal climatic variability (e.g., PDO) Forests may acclimate to new conditions Problems switching from wet to dry?

Atmospheric carbon dioxide concentrations Will higher CO2 levels reduce forest water use?

Climate change – temperature/precipitation

Simulation model approach

Identify likely hydrological impacts of: Vegetation changes Climatic variability

and change Soils and

topography

Integrate results across the region

Hydrological responses

Snowpack water storage and snowmeltSoil water storage Infiltration versus runoff Summer water deficits – severity and

duration of plant stress

Transpiration and evaporationRunoff and baseflow

Forest cover changes due to forest harvest and regrowth

Brush cover(post-harvest)

Mature forest(50-60 yr)

Mica – Potlach Watershed, Idaho, 1933-1990

Forest cover and snowpack

As forest coverincreases…

… spring snowpack declinesby up to 20%March 1 May 1

Forest density affects water use and soil water storage

Forest density affects surface runoff and baseflow

Questions to be addressed…

How will future climate and vegetation changes affect surface water fluxes and soil water storage in PNW forests?Which has a bigger impact on forest hydrology – climatic variability or vegetation change?What are the hydrological implications of changes in forest management practices?How might future changes in water resources affect forest productivity and species composition?

Presentation OutlineForest – water interactions Forest dependence on water resources Forest influences on water resources

Effects of land-cover change and climate on water cycling in PNW forest ecosystems Types and effects of land-cover changes Effects of climatic variability Interactions between climate and forest cover