Combined Effects of Heat and Drought on California Ecosystems under A Changing Climate

Authors: Chunyu Dong*, Sun Yat-sen University, Glen M MacDonald, University of California, Los Angeles, Gregory S Okin, University of California, Los Angeles, Thomas W Gillespie, University of California, Los Angeles
Topics: Hazards and Vulnerability, Water Resources and Hydrology, Climatology and Meteorology
Keywords: drought; Mediterranean-type ecosystems; NDVI; PDSI; California; climate change
Session Type: Paper
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A combination of drought and heatwaves is projected to occur more frequently over many areas in the future. The combined heat and drought stress may significantly affect vegetation health than drought stress alone. Recently, California has experienced three times of extreme droughts coupled with high temperatures, which provides opportunities to investigate the impacts of high temperatures on drought sensitivity of the Mediterranean climate vegetation. Here we investigate the spatial and seasonal patterning of greenness anomalies and trends for chaparral, coastal sage scrub, grassland, forest-woodland, and developed land using satellite data. We analyze the contrasting responses of the vegetation types to drought based on analyses of the Normalized Difference Vegetation Index (NDVI) anomalies and the Palmer Drought Severity Index (PDSI). We utilize a novel bootstrapping regression approach to decompose the relationships between the vegetation sensitivity (NDVI–PDSI regression coefficients) and the principle climate factors (temperature and precipitation) associated with the drought. We find significantly increased drought sensitivity in warmer locations, indicating the important role of temperature in exacerbating vulnerability; however, precipitation variations do not demonstrate significant effects. Chaparral seems to be the most vulnerable community to warming, while CSS will probably be also severely affected by the hotter droughts in fall and winter. Grassland and developed land are less responsive to warming. The elevated temperatures may alter vegetation distribution in California, as well as possibly increase annual grassland cover and decrease the extent and ecological services provided by perennial woody Mediterranean climate ecosystems.

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