Plant responses to changing rainfall frequency and intensity

Regardless of annual rainfall amount changes, daily rainfall events are becoming more intense but less frequent with anthropogenic warming. Larger rainfall events and longer dry spells have complex and sometimes opposing effects on plant photosynthesis and growth, challenging abilities to understand broader consequences on the carbon cycle. In this Review, we evaluate global plant responses to rainfall regimes characterized by fewer, larger rainfall events across evidence from field experiments, satellites and models. Plant function responses vary between −28% and 29% (5th to 95th percentile) under fewer, larger rainfall events, with the direction of response contingent on climate; productivity increases are more common in dry ecosystems (46% positive; 20% negative), whereas responses are typically negative in wet ecosystems (28% positive; 51% negative). Contrasting responses in dry and wet ecosystems are attributed to nonlinear plant responses to soil moisture driven by several ecohydrological mechanisms. For example, dry ecosystem plants are more sensitive to large rainfall pulses compared with wet ecosystem plants, partly driving dry ecosystem positive responses to fewer, larger rainfall events. Knowledge gaps remain over optimal rainfall frequencies for photosynthesis, the relative dominance of rainfall pulse and dry spell mechanisms and the disproportionate role of extreme rainfall pulses on plant function. Rainfall events are becoming less frequent but more intense with anthropogenic warming. This Review explores the consequences of these changes on plants and investigates how and why plant responses appear to broadly differ between dry and wet ecosystems.