StressorsPNW_ClimateChange
National Multiple Stressors Project – Pacific Northwest Region ONLYLast Updated: August 8, 2014By: Michelle DayGeneral Process – National Maps (800 m resolution)In an effort to combine disturbances that affect the US, we examined wildfire, insects and disease, urban and exurban development, and climate change to describe where these “stressors” occur individually and where they occur in combination. Originally layers were reclassified to define locations “at risk” and “not at risk” based on predetermined thresholds (Table 1). We then used a roving circular neighborhood analysis to identify locations where stressors may be more concentrated relative to others and to identify where multiple stressors intersect. Table 1. Selected disturbances (“stressors”), source, resolution and selected risk thresholdDataSourceResolutionTimespanThreshold (“at risk”)Basal area lossFHTET240 m2012-2027≥25%Housing density (2030)SILVIS Labcensus block2030≥6.17 housing units/km2Wildland fire potentialRMRS270 mcurrenthigh and very highClimate Change SEDNASA, Kim30 arc sec (~800m)1960-2099*national median*Climate change layer compares historical period (1960-1989) with future (2070-2099)ScaleAll of the above layers (except climate) were developed for planning purposes at coarse scales. The housing density layer specifies the data are too coarse for even county or township-level land use planning, given finer-scaled local data are usually available. The basal area loss layer specifies it should not be used for on-the-ground implementation. The wildland fire potential layer specifies it can be used for landscape (100s of square miles) or national analyses. NASA’s climate data page does not indicate appropriate scale.For the current output we have selected to use a scale based on county sizes across the US. At least 50% of the counties within the lower 48 must meet our selected size. For a roving circular neighborhood analysis, 72% of the counties meet the 20 km radius selected scale.ResolutionThe original resolution of the data differs by source (see Table 1). These data were processed at the coarsest raster scale (800 m) using the Albers Conical Equal Area projection (NAD83 Albers). Basal area loss and wildland fire potential were resampled to 800 m using the majority value (recommended for discrete data). Climate data were reprojected to the Albers projection which resulted in a slight resampling (nearest). Due to differing extents among layers (principally between the climate layer and the other 2 rasters), layers were masked to a project-level mask to ensure matching extents.The housing density data are polygon-based census blocks. Blocks vary in size; the mean size is 222.4 ha (2.2 km2), but ranges from tiny slivers (0.0018 ha for an inhabited parcel) to a large uninhabited polygon (11.7 million ha; 11, 727 km2). The largest inhabited polygon is 709,780 ha. These data were rasterized based on majority area at the 800 m grid size, clipped and snapped to the mask layer developed for the project. Note that Theobald et al. (2007) rasterized census data to 1 ha grid using the centroid method.Binary ThresholdsOriginal data were converted to binary layers where stressors were defined as “at risk” or “not at risk” based on published standards or upon examination of the data (i.e., only in the case of climate; see Table 1). Note that the “risk” threshold for housing density has been changed from 8 housing units per sq. km as published in Kline et al. (2013) to 6.17 to match the WUI standard in Radeloff et al. (2005) and recent Forest From the Edge reports. This value was based on the definition of intermix WUI in the Federal Register (1 housing unit per 40 acre parcel). The basal area loss threshold was already defined and provided as a binary layer from FHTET based on the 25% threshold.Focal Statistic Thresholds – Pacific Northwest RegionThe following thresholds were calculated for displaying the final risk maps using the regional mean and standard deviation from 20 km radius focal statistic (neighborhood analysis) outputs.Table 2. Selected disturbances (“stressors”), risk thresholds, and focal statistic output means and standard deviations for the Pacific Northwest Region.LayerThresholdMeanStdvMean+Stdv20k Display (%)Basal Area Loss≥ 25%0.0800010.1453630.22536423Housing Density≥6.17 HUs/sq km0.189070.2023710.39144139Wildland Firehigh, very high0.1058120.1950490.30086130Climate Changemedian, 3.840.1587970.2984710.45726846
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