Figure 1: Interannual variations in anomalies of total NPP and average SPEI.

(a) Relationships between annual NPP and annual SPEI in both hemispheres. (b) Correlation coefficients (Pearson coefficient, R) between annual NPP and 12- to 24-month SPEI. (c) Relationship between annual NPP and 19-month SPEI in the Northern Hemisphere. (d) Relationship between annual NPP and 16-month SPEI in the Southern Hemisphere. **Denotes 95% confidence level estimated with a t-test; ***denotes 99% confidence level estimated with a t-test.