Synchronous crop failures and climate-forced production variability

Abstract

Large-scale modes of climate variability can force widespread crop yield anomalies and are therefore often presented as a risk to food security. We quantify how modes of climate variability contribute to crop production variance. We find that the El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), tropical Atlantic variability (TAV), and the North Atlantic Oscillation (NAO) together account for 18, 7, and 6% of globally aggregated maize, soybean, and wheat production variability, respectively. The lower fractions of global-scale soybean and wheat production variability result from substantial but offsetting climate-forced production anomalies. All climate modes are important in at least one region studied. In 1983, ENSO, the only mode capable of forcing globally synchronous crop failures, was responsible for the largest synchronous crop failure in the modern historical record. Our results provide the basis for monitoring, and potentially predicting, simultaneous crop failures.

Fig. 1. El Niño climate teleconnections in JAS (July, August, September), NDJ (November, December, January), and MAM (March, April, May).

Partial regression coefficients for the standardized ENSO time expansion coefficients 1 + 2 (A₁ * σ_A1 + A₂ * σ_A2 in Eq. 2) from the multilinear regression analysis. Partial regression coefficients are shown for three stages in the life cycle of an El Niño event: a developing El Niño (A), a mature El Niño (B), and a decaying El Niño (C). Colors are sea surface temperature anomalies (in °C) of the ocean and soil moisture anomalies (in kg/m²) over land; contours are 200-hPa geopotential height anomalies (contours every 5 hPa), and vectors are winds at 925 hPa.

Fig. 2. Climate teleconnections for the Indian Ocean Dipole (IOD), Tropical Atlantic Variability (TAV), and North Atlantic Oscillation (NAO).

Partial regression coefficients for the standardized IOD, TAV, or NAO time expansion coefficients (A_k * σ_Ak in Eq. 2) on dependent climate variables. IOD coefficients during JAS (A) and NDJ (C). The NAO coefficients for DJF (B) and TAV coefficients during May, June, and July (D). Colors are SST anomalies of the ocean (in °C) and soil moisture anomalies over land (in kg/m²). Contours are 200-hPa geopotential height anomalies (contours every 5 hPa for TAV and IOD and every 15 hPa for NAO), and vectors are winds at 925 hPa.

Fig. 3. Local production variance associated with climate modes.

Harvested area of wheat, maize, and soybean with numbered boxes indicating regions for the variance analysis (A). Percent of national or subnational scale variance in each region for wheat (B), soybean (C), and maize (D) explained by the ENSO (El Nino Southern Oscillation), IOD, TAV, or NAO. The percent values on top of each bar indicate the total variance explained by modes of climate variability (ENSO + TAV + IOD + NAO).

Fig. 4. Production variance associated with climate modes at the global scale and disaggregated by production quartile.

Percent variance explained by each climate mode in the global domain when production variance is measured at the national or subnational scale (“local”) or measured in the globally aggregated time series (“global”) for maize (A), soybean (C), and wheat (E). See Materials and Methods for details. Percent of local variance explained disaggregated by average absolute production (in kg) quartile for maize (B), soybean (D), and wheat (F). Results ordered from lowest-production quartile (q1) to highest-production quartile (q4). Colors refer to variance related to the ENSO, IOD, TAV, or NAO.

Fig. 5. Observed and ENSO-forced yield anomalies during the largest synchronous crop failure in modern historical record.

Observed (A) and ENSO-forced (B) percent crop yield anomalies in 1983, which has been identified (10) as the most extensive synchronous crop failure in modern (after 1960) record, and maize production anomalies (C) by country. Both the spatial pattern and globally aggregated values indicate that ENSO played a major role in forcing synchronous crop failures in 1983. Observed crop yield anomalies are characteristic of an El Niño transitioning to a La Niña, as was the case in 1983 (compare to maize yield anomalies in fig. S1).