Drought intensity and duration interact to magnify losses in primary productivity

Terrestrial ecosystem productivity losses are expected to magnify over time with increased drought duration, a likely future scenario. Yet, some ecosystems appear resistant to progressive losses in productivity with multi-year drought. We quantified the combined effects of drought duration and severity on aboveground productivity in 74 grasslands and shrublands. Productivity declined 29% when drought severity was within the range of historic variability, with little evidence for progressive loss over time. Resistance was lost when drought severity was extreme (≤ 1-in-100-year likelihood). When extreme drought occurred over consecutive years, productivity losses increased 3-fold. Our results portend a shift in ecosystem behavior under future drought scenarios – from maintenance of reduced functioning over time to progressive and profound loss of functioning as drought duration and severity increase.