Interactions between fire, climate, and sediment generation in the Pacific Northwest Presented by Dennis P. Lettenmaier Climate Impacts Group Seminar February 1, 2005

Presentation Outline Motivation and experimental description Hydrology and sediment modelling Fire modelling Model application location Conclusions and future work

Motivation Photo from US Geological Survey

Motivation Increased sediment flows impact society and ecosystems Siltation of dams and structures Decreased transportation capacity in rivers Degradation of salmonid spawning habitat Increased nutrient transportation

Motivation Timing of large storms and wildfires affect sediment generation McNabb and Swanson, 1990

Experimental description Create hydrologic model of eastern Cascades basin Force model with long-term (~85 years) meteorological record Create stochastic fire history sequences for the basin equal in burned area Evaluate differences in sediment generation based on timing of fires and storms

Hydrology and sediment model- DHSVM Photo from US Geological Survey

Distributed hydrology-soil-vegetation model (DHSVM) Physically based hydrologic model that represents the effects of –Topography –Soil –Vegetation –Solves the energy and water balance at each grid cell at each timestep

DHSVM SURFACE EROSION CHANNEL EROSION & ROUTING Watershed Sediment Module OUTPUT Q Q sed Provides Inputs for all Three Components MASS WASTING Watershed Sediment Module Sediment Model

Stochastic fire model Photo from USDA Forest Service

Fire Model Structure Stochastic Prediction of Area, Size, and Mapped Severity-SPASMS 1. Predicts the number of fires within a given time period 2. Selects the size of each fire 3. Selects the year and day of each fire 4. Distributes the fire upon the landscape

Prediction of a fire sequence Based on a Poisson distribution modified from Agee (1993) Where: X is a discrete number of fire events; P(X=k) is the probability that k events will occur in a given time period; a is the Poisson parameter, estimated by the average number of occurrences. Requires mean time between fires over the basin The time until the next fire is selected from an exponential distribution

Fire size selection Select corresponding fire size from a probability distribution Example distribution generated from Teanaway River (E. Cascades) data of Wright and Agee (2004) Data consists of 433-year fire history based on fire scars in a ~30,000 ha sample area Size distribution used is based upon summer soil moisture

Fire size selection (cont)

Climate effects on fire size

Climate effects on fire size, (cont)

Spatial distribution of fire Randomly selects center pixel from vegetation cells with specified fire regime Places fire in a square pattern centered on selected pixel Allows fires to leave basin Fire severity for mixed severity fire regimes is selected in a ratio approximately equal to a user- specified ratio between low, medium and high severity

Model application Photo from USDA Forest Service

Entiat River watershed

Hydrology model implementation Create 85-year hydrological record of the Entiat River based upon Hamlet and Lettenmaier (2004) data Read maps of disturbances Dynamically update LAI and root cohesion following disturbance events

Fire model implementation Create fire model of the Entiat basin based upon potential vegetation types (Washington GAP project, Cassidy, 1997) Three fire regimes within basin (Agee, 1993) High severity: long return period, stand replacement fires (Subalpine zones) Low severity: frequent, low severity fires (Lower elevations, veg. such as Ponderosa pine) Mixed severity: mixture of high, low and medium severity fires. Frequency between high and low severity regimes. Medium elevations and vegetation such as grand fir Adjust fire size distributions to match fire studies in the Entiat (Everett et. al., 2000, 2003; Schellhaus et. al. 2001) Generate a large number of fire sequences; select sequences of similar total burned area and create fire severity maps for each sequence

Entiat basin fire regime map

Summary and future work Conclusions: Creation of fire sequences with similar burned area but different timing allows examination of the interaction between fires and large storm events Maintains inter-annual climate variability Future Work: Examine future climate scenarios Examine forest management scenarios

References Agee JK Fire Ecology of Pacific Northwest Forests, Island Press, Washington, D.C. Agee JK Fire and weather disturbances in terrestrial ecosystems of the eastern Cascades.General Technical Report PNW-GTR-320. Portland: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 52 p. Cassidy, K. M Washington Gap Project 1991 Land Cover for Washington State. Washington Cooperative Fish and Wildlife Research Unit, University of Washington Cook, E.R., 2000, North American Drought Variability PDSI Reconstructions. International Tree-Ring Data Bank. IGBP PAGES/World Data Center-A for Paleoclimatology Data Contribution Series # NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. Cook, E.R., Meko, D.M., Stahle, D.W. and Cleaveland, M.K Drought reconstructions for the continental United States. Journal of Climate, 12: Doten, C.O., and D.P. Lettenmaier, Prediction of sediment erosion and transport with the Distributed Hydrology-Soil-Vegetation Model, WRS Series Technical Report No. 178, Department of Civil and Environmental Engineering, University of Washington (available at of sediment erosion and transport with the Distributed Hydrology-Soil-Vegetation Model Everett RL, Schellhaas R, Ohlson P, Spurbeck D, Keenum D Continuity in fire disturbance between riparian and adjacent sideslope douglas- fir forest. Forest Ecology and Management, 175(1-3): Everett RL, Schellhaas R, Keenum D, Spurbeck D, Ohlson P Fire history in the ponderosa pine/Douglas-fir forests on the east slope of the Washington Cascades. Forest Ecology and Management 129: McNabb DH and Swanson FJ 1990, Effects of fire on soil erosion, from natural and prescribed fire in Pacific Northwest Forests, Walstad, JD, Radosevich SR, and Sandberg DV, eds. Corvallis: Oregon State University Press. Schellhaas R, Spurbeck D, Ohlson P, Keenum D, Riesterer H Fire disturbance effects in subalpine forests of north central Washington. USDA Forest Service Region 6 Okanogan and Wenatchee National Forests, Wenatchee, WA. Wigmosta, M.S., L.W. Vail, and D.P. Lettenmaier, 1994: A distributed hydrology-vegetation model for complex terrain, Water Resour. Res., 30, Wright CS and Agee JK Fire and vegetation history in the eastern Cascade Mountains, Washington. Ecological Applications, 14: