The El Niño event is the second most important factor influencing our crop weather in the Midwest. If the El Niño is going on, the drought will not begin. Historically, we have not detected a widespread drought in the Corn Belt when an El Niño event was in progress.

When the El Niño is going on, the airflow from the Gulf of Mexico may be somewhat stronger. And in fact, the Canadian flow may also be stronger, so there could be a cooler than usual summer, because of the flow of northerly air, but also the air collides with moisture from the Gulf. Increased precipitation results near the Gulf of Mexico and sometimes pushes as far north as Iowa. Southern Iowa and Missouri might expect increased August moisture during an El Niño year. And from Des Moines north, a little bit cooler than usual summer, or at least not warmer than usual. This would be the normal weather pattern expected during the summer and strengthened during an El Niño year.

The El Niño event itself has to do with warmer than usual water in the Central and Eastern Pacific Ocean (Figure 1.23). That warm water results in more evaporation of water and more rain than usual over Tahiti. Tahiti would normally receive 2 or 3 inches of water during the year and occasionally 5. During El Niño conditions it might receive 20-50 inches of precipitation. So when the El Niño is going on, there will be more rain in the center of the Pacific, less rain in Australia, and hot and perhaps dry conditions in southeast Asia (from India to Korea and Japan would be typical).

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Fig. 1.23 Satellite-measured sea surface temperature deviation from long-term average. Note warm anomaly across the eastern Pacific Ocean near the equator.

If we would look at the entire world during an El Niño, there is typically a drought going on in southeast Africa, floods on the equator in Africa, harsh conditions from India to Korea, and warm winters from Alaska to Nebraska (they may influence Iowa). When the El Niño is going on, the summer will be a little cooler than usual from Des Moines north. And it may be wetter than usual from Des Moines south (Figure 1.22).

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Fig. 1.24 El Niño effects on worldwide climate.

In South America, there is normally plenty of moisture where they grow the corn and soybeans. In Peru where El Niño gets its name, the El Niño is a wet year.

The sea surface temperature anomalies alternate sides of the Pacific during a La Niña, or opposite of El Niño, the western Pacific becomes warmer than normal. Australia becomes wet; Peru becomes dry. Conditions are reversed from those in Figure 1.24. These two extremes alternate on a 2-7 year cycle.