Water yield increase from regular fire in longleaf

This GIS layer predicts annual increases in water yield in gallons/acre when going from a longleaf stand that hasn’t been burned for 10+ years to one with a burn within the last 6 years. It uses PRISM data for precipitation, MODIS data for potential evapotranspiration, and field data from North Florida to estimate difference in evapotranspiration based on fire return interval. It uses the equations in the WASSI ecosystem services model to estimate change in water yield (https://www.fs.usda.gov/ccrc/tools/wassi).

Note: this layer covers the historic range of longleaf but does not mask out areas within that range unlikely to support longleaf (e.g., lakes, freshwater wetlands, etc.).

Input data

• Potential evapotranspiration (PET) from MODIS (http://www.ntsg.umt.edu/project/modis/mod16.php)
• Precipitation from PRISM (30yr normal, 800m resolution, http://prism.oregonstate.edu/normals/)
• Historic Longleaf Pine extent (https://databasin.org/datasets/f68160cd267f47f7adc1caa04465b248)
• Predicted change in Leaf Area Index (LAI) from Jensen and Gatrell 2004 (https://www.tandfonline.com/doi/abs/10.2747/1548-1603.41.2.155?journalCode=tgrs20)

Mapping steps

• Processing Potential Evapotranspiration (PET)
  • Set NoData 32767.000000
  • Fill in NoData based on surrounding values
    • Raster calculator: Con(IsNull(“raster”), FocalStatistics(“raster”, NbrRectangle(5,5, “CELL”), “MEAN”), “raster”)
  • Clip to longleaf range to speed up resampling
  • Resample to 200m
• Processing Precipitation (P)
  • Resample to 200m
• Predicting change in water yield
  • Use equation from WaSSI water balance model (https://www.fs.usda.gov/ccrc/tools/wassi) to predict change in water yield: ET = 0.174*P + 0.502*PET + 5.31*LAI + 0.0222*PET*LAI
  • Calculate water yield change from WaSSI model for each month based on P, PET, and LAI. Example ArcGIS code from September:
    • (0.174*“US PRISM 200m\Sep_PRISM_ppt_200m.img”*10+.502*“Longleaf MODIS 200m\Sep_MODIS_00_14_filled_longleaf_200m.img”+5.31*1.05+0.0222*“Longleaf MODIS 200m\Sep_MODIS_00_14_filled_longleaf_200m.img”*1.93)-(0.174*“US PRISM 200m\Sep_PRISM_ppt_200m.img”*10+.502*“Longleaf MODIS 200m\Sep_MODIS_00_14_filled_longleaf_200m.img”+5.31*1.05+0.0222*“Longleaf MODIS 200m\Sep_MODIS_00_14_filled_longleaf_200m.img”*1.05)
  • Add together monthly layers to get yearly water yield change
  • Convert WaSSI water yield change estimates to gallons/acre
    • 1/0.00024711)*(“wassi_burndif.tif”/1000)*264.17

Known issues

• Predicted change in Leaf Area Index (LAI) from burning is only based on one site in North Florida.