1.Global warming intensifies the hydrological cycle and may result in changes in the frequency and intensity of precipitation events. However, a knowledge gap still exists about the general influences of intra-annual precipitation variability on grassland plant diversity and ecosystem function at the global scale.

2.Here, we synthesized field manipulative experiments from 66 publications to quantify the effects of intra-annual precipitation variability increases (IPVI) on community biomass and plant diversity in grasslands worldwide.

3.At the global scale, we found that IPVI generally increased grassland community above-ground biomass (AGB) by 6.90%, and decreased grass biomass and soil ammonium content by 10.38% and 25.35% respectively. IPVI increased and decreased total AGB in arid and humid regions, respectively, and IPVI enhanced grassland below-ground biomass and plant species richness in arid regions, but showed no effect in humid regions. Furthermore, moderate IPVI stimulated plant species richness and community biomass in arid grasslands, while extreme IPVI impaired them in mesic grasslands. Changes in total AGB under IPVI were related to changes in the biomass of plant functional groups, species richness and soil moisture. Structural equation modelling demonstrated that climate conditions (mean annual temperature and mean annual precipitation) and background soil properties (soil sand content and soil organic carbon content) jointly regulated grassland total AGB responses to IPVI across climate regions.

4.Synthesis. Overall, our study shows divergent responses of grassland productivity and diversity to IPVI in arid and humid regions. Accounting for climate, edaphic properties and precipitation variability can help improve our ability to predict the responses of grassland ecosystems to future changes in precipitation at global scales.