Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Drought is a global issue that is exacerbated by climate change and increasing anthropogenic water demands. The recent occurrence of drought in California provides an important opportunity to examine drought response across ecosystem classes (forests, shrublands, grasslands, and wetlands), which is essential to understand how climate influences ecosystem structure and function. We quantified ecosystem resistance to drought by comparing changes in satellite-derived estimates of water-use efficiency (WUE = net primary productivity [NPP]/evapotranspiration [ET]) under normal (i.e., baseline) and drought conditions (Delta WUE = WUE2014 - baseline WUE). With this method, areas with increasing WUE under drought conditions are considered more resilient than systems with declining WUE. Baseline WUE varied across California (0.08 to 3.85 g C/mm H2O) and WUE generally increased under severe drought conditions in 2014. Strong correlations between Delta WUE, precipitation, and leaf area index (LAI) indicate that ecosystems with a lower average LAI (i.e., grasslands) also had greater C-uptake rates when water was limiting and higher rates of carbon-uptake efficiency (CUE = NPP/LAI) under drought conditions. We also found that systems with a baseline WUE <= 0.4 exhibited a decline in WUE under drought conditions, suggesting that a baseline WUE <= 0.4 might be indicative of low drought resistance. Drought severity, precipitation, and WUE were identified as important drivers of shifts in ecosystem classes over the study period. These findings have important implications for understanding climate change effects on primary productivity and C sequestration across ecosystems and how this may influence ecosystem resistance in the future.711National Science Foundation at the National Center for Ecological Analysis and Synthesis (NCEAS), a center - University of California, Santa Barbara [OCI-1216894]State of CaliforniaNCEASMICINN (Spanish Government) [PTA 2011-6322-I]USAIDU.S. Department of State through the Sustainable landscapes Brazil programAustralian Research Council [DE140101608]Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)