Extended Data Figure 3: Classification of extreme dry, moderate dry, normal, moderate wet, and extreme wet years for each year of the 46 experiments.

The 12-month version of the SPEI is shown, where positive values indicate wetter than normal water balances (precipitation minus potential evapotranspiration) during the 12-month time interval preceding and including the month of peak biomass harvest. For example, if peak biomass was harvested in September, then SPEI-12 accounts for the water balance from the previous October to September. Drought index values are based on month-by-month variations in climate over the past century (January 1901 to December 2011), based on monthly means of measurements made at more than 4,000 weather stations worldwide, and provided on 0.5 degree × 0.5 degree grids globally. Dashed lines show cutoffs for 1 in 4 (±0.67) or 1 in 10 (±1.28) year events. Seven experiments that included only normal years (Agrodiversity Germany a, Agrodiversity Ireland a, Czech Republic) or that did not include any normal years (Agrodiversity Poland a, Agrodiversity Spain a, Iowa BioGEN, North Dakota a) were excluded from subsequent analyses because it was not possible to compare perturbed with normal productivity levels for these studies.