Temporal Variations of NDVI and LAI and Interactions With Hydroclimatic Variables in a Large and Agro‐Ecologically Diverse Region

Abstract

AbstractSatellite based vegetation indices are increasingly used to characterize vegetation's response to climate variability and change over large spatial extents. The use of a given index assumes that the index adequately describes the vegetation's response to hydroclimatic forcing. The objective of this study is to compare the temporal behaviors of normalized difference vegetation index (NDVI) and leaf area index (LAI) and their associations with hydroclimatic variables. Observations of monthly precipitation, streamflow, temperature, vapor pressure deficit, evapotranspiration, and total water storage anomalies (TWSA) are processed for the combined Sacramento River and San Joaquin River basins in California for 13 water years (October 2002 to September 2015). Estimates of NDVI and LAI are obtained for the same period from MODerate resolution Imaging Spectroradiometer (MODIS). The seasonal cycle of NDVI peaks 2–3 months earlier than LAI. The seasonal variation in NDVI follows the seasonality of TWSA (i.e., water availability) whereas the seasonal cycle of LAI follows the seasonality in mean temperature and vapor pressure deficit (i.e., atmospheric water demand). Cross‐correlation analyses of NDVI and LAI with the hydroclimatic variables show that LAI is more strongly correlated with most of the hydroclimatic variables considered.