Intra-annual precipitation variability mutes or magnifies the impact of wet and dry years on plant biomass.
As the atmosphere warms, both the amount and timing of precipitation are changing, but how those two trends interact to influence plant growth remains unresolved. Using 5-15 years of data from 48 globally distributed grassland sites, we quantified how the temporal distribution of precipitation within the year (evenness) interacts with annual precipitation amount and nutrient limitation to influence plant biomass. Annual precipitation anomalies had a large influence on plant biomass when intra-annual precipitation was more evenly distributed (frequent small events) and little impact when less even (infrequent large events). This relationship was consistent across aridity gradients and nutrient limitations and strongest in systems with warm wet seasons. Our work shows that the response of plant systems to changes in annual precipitation amount are largely dependent on how evenly it is temporally distributed.