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Climatic variability, land-cover change, and forest hydrology in the Pacific Northwest

Climatic variability, land-cover change, and forest hydrology in the Pacific Northwest. David W. Peterson JISAO Climate Impacts Group Forest Hydrology. Current Research: Climate – Water – Forest Interactions. Climate. Water. Forests. Water and ecosystem productivity. Gross photosynthesis.

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Climatic variability, land-cover change, and forest hydrology in the Pacific Northwest

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  1. Climatic variability, land-cover change, and forest hydrology in the Pacific Northwest David W. Peterson JISAO Climate Impacts Group Forest Hydrology

  2. Current Research:Climate – Water – Forest Interactions Climate Water Forests

  3. Water and ecosystem productivity Gross photosynthesis Annual Outflow Numeric Terradynamics Simulation Group University of Montana

  4. Forest dependence on water resources in the PNW • Trees require water for photosynthesis and growth • Summer water deficits limit forest productivity • Total precipitation • Seasonality of precipitation • At high elevations, excessive snowpack limits growing season length and forest productivity • Water availability influences forest species composition and density

  5. 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

  6. Water and ecosystem productivity Gross photosynthesis Annual Outflow Numeric Terradynamics Simulation Group University of Montana

  7. 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

  8. 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

  9. Simulation model approach • Identify likely hydrological impacts of: • Vegetation changes • Climatic variability and change • Soils and topography • Integrate results across the region

  10. Hydrological responses • Snowpack water storage and snowmelt • Soil water storage • Infiltration versus runoff • Summer water deficits – severity and duration of plant stress • Transpiration and evaporation • Runoff and baseflow

  11. Forest cover changes due to forest harvest and regrowth Brush cover (post-harvest) Mature forest (50-60 yr) Mica – Potlach Watershed, Idaho, 1933-1990

  12. Forest cover and snowpack As forest cover increases… … spring snowpack declines by up to 20% May 1 March 1

  13. Forest density affects water use and soil water storage

  14. Forest density affects surface runoff and baseflow

  15. 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?

  16. Presentation Outline • Forest – 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

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