Effects of Drought on Terrestrial Primary Productivity in Southern California

For the past few years, Southern California has been experiencing extended drought. These conditions are unfavorable to the growth and health of most types of terrestrial vegetation. We hoped to gain insight into potential ecosystem changes as well as possible disturbances to the terrestrial carbon cycle by exploring changes in gross primary productivity (GPP) over time and space in different plant types. We analyzed time series of GPP over the past five years derived from the MODIS sensor at four field sites: Coal Oil Point Reserve, Sedgwick Airstrip, Mission Canyon, and Painted Cave. We also assessed the relationship between GPP and the drought with other MODIS products, such as vegetation indices and fraction of photosynthetically active radiation (fPAR). Furthermore, we studied higher resolution spatial effects of the drought using Landsat data from spring 2011, 2013, and 2015. The images were classified by plant type and the results were used in a light use efficiency (LUE) model. The values for photosynthetically active radiation (PAR) were based on data collected at one of the field sites; fPAR was calculated from the images using a linear regression with the normalized difference vegetation index (NDVI). While some individual sites showed minimal changes in GPP, widespread GPP trends indicate a drop in primary production due to the drought.

Presentation Slides: Effects-of-Drought-on-Terrestrial-Primary-Productivity-in-Southern-California