Fig. 3: Influence of El Niño and co-occurring modes of variability on regional drought characteristics.

Observed (1981–2018; filled circles) and simulated (boxplots and unfilled circles) distribution of a drought area and b drought intensity in each SREX region during neutral (gray), Niño3.4⁺ (green) and co-occurring (orange) conditions. Neutral conditions represent summer (June–September) seasons with neutral phases (< ± 0.5 σ) of the four modes of variability considered. Niño3.4⁺ conditions represent seasons with SST anomalies >0.5σ over the Niño3.4 region only and other modes in their neutral phases. Co-occurring conditions include summer seasons with Niño3.4⁺ conditions co-occur with either cold Atlantic Niño SST anomalies (<−0.5σ), cold TNA SST anomalies (<−0.5σ) or positive IOD (DMI >0.5σ) conditions, consistent with the phases of these modes that are associated with droughts in most regions. Gray arrows indicate significant differences in the mean of distribution of drought area and intensity during Niño3.4⁺ or co-occurring conditions relative to neutral conditions at 5% significance level. Green arrows indicate significant differences in the mean of distributions between Niño3.4⁺ and co-occurring conditions at 5% significance level. Black dots show the mean of the distribution in each boxplot. Significance of the difference in the drought characteristics between Niño3.4⁺ and co-occurring conditions in observations is not estimated due to small sample sizes. There are 2 Niño3.4⁺ and 7 co-occurring conditions in observations and 27 Niño3.4⁺ and 426 co-occurring conditions in the CESM pre-industrial simulation.