PS 29-164 - Biophysical parameters and tree canopy cover across an urban suburban gradient: Patterns and relationships to prolonged drought

Tuesday, August 8, 2017
Exhibit Hall, Oregon Convention Center
Tracy L. Benning1, Mary L. Cadenasso2 and Bryn R. Montgomery2, (1)Environmental Science, University of San Francisco, San Francisco, CA, (2)Department of Plant Sciences, University of California, Davis, Davis, CA

In urban landscapes, prolonged drought and responsive water conservation practices can have profound effects on vegetation cover, productivity, and evapotranspiration. The impact of drought, however, may vary with location within the urban matrix. We evaluated the effects of drought on NDVI and land surface temperature (LST) in residential areas along an urban to suburban transect (UST) spanning 36 km from downtown Sacramento, CA eastward towards the Sierra foothills. Our primary goal was to examine how NDVI and LST differed amongst patches of variable tree canopy cover along the UST in response to drought. The HERCULES land cover model categorized patches into five tree canopy cover classes -- 0-10%, 10-20%, 20-30%, 30-40%, and 40-100%. Using Landsat imagery, NDVI and LST were calculated for the study transect during February, April, July, and December in 2009 and 2010 under pre-drought conditions and again in 2014 and 2015 after 3 years of drought. These four months capture bud break, peak growing season, dry season, and senescence, respectively. NDVI and LST values were extracted using the HERCULES canopy cover patches; and the Zonal Statistics tool in ArcGIS was used to calculate aggregated summary statistics for all patches in each canopy cover class.


Results from preliminary analyses along the UST show a clear response by both NDVI and LST after 3 years of prolonged drought. Seasonally averaged patch aggregates of both NDVI and LST follow the expected trends within each canopy cover class with peak NDVI values occurring in April in normal to above normal water years. The range in average NDVI values span from 0.15 in the 0-10% cover class to 0.35 in the 40- 100% class. LST values peak in July for those same years with a range of average values from 33o C in lowest cover class to 29o C in the highest cover class. After 3 years of drought conditions throughout the study area, peak NDVI values unexpectedly shift to July for all cover classes but with typically lower average values ranging from 0.14 to 0.27 while LST values remain highest in July. Average surface temperatures are much warmer though with LST values ranging from 44o C in lowest cover class to 40o C in highest cover class. Further analyses will examine drivers of these patterns within specific cover classes and patch types along the UST.