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El Niño event likely to result in decreased rainfall in Central America and the Caribbean

  • Special Report
  • Latin America and the Caribbean
  • July 9, 2014
El Niño event likely to result in decreased rainfall in Central America and the Caribbean

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  • Key Messages
  • Understanding El Niño
  • El Niño Forecast
  • El Niño Impacts
  • Key Messages
    • According to forecasts provided by the U.S. National Multi-Model Ensemble (NMME) and the Climate Prediction Center-International Research Institute for Climate and Society (IRI), there is a 65 percent probability that El Niño conditions will develop over the three-month period from July to September. An El Niño event typically lasts between 8 to 10 months.

    • Due to the expected El Niño event, decreased rainfall is projected for the Central American Pacific region during the July to December 2014 period, primarily affecting the dry corridor in Nicaragua, Honduras, El Salvador, and Guatemala. Maize crops planted in the Primera season (May-August) in Central America are likely to be negatively affected during the final stages of crop development due to a prolonged canícula.

    • The Postrera season (August-December) is likely to begin in many areas with below-average rainfall, thereby delaying planting dates and disrupting seasonal sowing schedules. Postrera harvests of beans – the main crop planted in the Central America Pacific Basin during this season – are likely to be below-average due to the expected poor start of rains and below-average rainfall over the course of the season.

    • Irregular, low-intensity rainfall is projected for Haiti, primarily in the western and northern regions, from late June through December 2014. Areas previously affected by the scant rainfall recorded in 2013 will again likely be affected by poor spring and fall 2014 seasons.

    • The continuation of El Niño conditions into 2015 could affect water availability for human and animal consumption and crop irrigation in Central America and Haiti.


    Understanding El Niño

    El Niño - Southern Oscillation (ENSO) is a naturally occurring phenomenon that involves fluctuations of sea surface temperatures (SSTs) and winds across the equatorial Pacific Ocean. In general, every three to seven years, ENSO varies between its three phases: El Niño, La Niña, and neutral conditions. It remains in each phase on average between eight and twelve months, though this time can be much longer. An El Niño occurs when the equatorial easterly (from east to west) winds over the Pacific are lighter than average, resulting in warmer than average SSTs in the central and eastern Pacific Ocean. La Niña occurs when the equatorial easterly winds over the Pacific are stronger than average, resulting in cooler surface water in the central Pacific Ocean. ENSO neutral conditions occur when the equatorial winds are near average strength, and when SSTs across both the eastern and central Pacific Ocean are also close to average. These ENSO-related changes in the equatorial Pacific Ocean are related to major weather and climate fluctuations around the world, with varying consequences for populations in different locations.

    El Niño affects the atmospheric circulations and precipitation globally, and its impacts are strongly felt over Central America and the Caribbean. Strong precipitation decreases relative to average typically occur during El Niño events over Central America and the Caribbean. The decrease in precipitation primarily affects subsistence farmers residing in areas of the Central American Pacific and in areas with limited rainfall (typically referred to as dry corridor areas), i.e., less than 850 millimeters per year. It also affects water availability in general, for both human and animal consumption.


    El Niño Forecast

    According to the NMME forecasts for SSTs over the eastern and central tropical Pacific Ocean and the most recent Climate Prediction Center-International Research Institute for Climate and Society Consensus Probabilistic ENSO Forecast, El Niño conditions will be met by late July 2014. Average SST forecasts by the NMME for August-October of 2014 (Figure 1) indicate warmer than average conditions across the eastern and central Pacific Ocean similar to the conditions identified by Johnson (2013)  (Figure 2).

    The El Niño SST pattern identified by Johnson (2013)* is historically related to strong precipitation decreases throughout Central America and the Caribbean from August to December (Figure 3). On average, the most substantial rainfall deficits have historically affected the Pacific-facing coastal areas of Guatemala, El Salvador, Nicaragua, and Costa Rica.

    *Johnson, Nathaniel C., 2013: How Many ENSO Flavors Can We Distinguish?. J. Climate, 26, 4816–4827. doi: http://dx.doi.org/10.1175/JCLI-D-12-00649.1


    El Niño Impacts

    During El Niño events in Central America, basic grains planted during the Primera season (May-August) are affected during the final crop development stages by a prolonged canícula.  The canícula typically has a duration of about 10 days during July-August but can last for an additional 20 or more days under El Niño conditions. This occurs primarily in the dry corridor. For areas under cultivation during the period from May to October, such as the Guatemalan Highlands (altiplano), the decreased precipitation brought on by a prolonged canícula occurs during a critical stage of plant growth, thus affecting production, as happened during the 2009 El Niño.

    Under El Niño conditions, the Postrera season (August-December) usually begins with below-average rainfall, delaying planting dates and disrupting seasonal sowing schedules. Throughout Central America, beans are most affected during this season. Rainfall for Postrera crops is expected to be below average over the course of the season.

    Decreased rainfall in Haiti is likely in the western and northern regions. Irregular and poorly distributed rainfall may affect crop development for both the spring (April-July) and fall (August-December) seasons.

    The hurricane season (June-November) is also affected by El Niño conditions, typically with a reduction in the number of hurricanes over the Caribbean and the Gulf of Mexico.

    Figures Figure 1. NMME forecast SST anomaly (°C) for August-December 2014 (produced June 2014)

    Figure 1

    Figure 1. NMME forecast SST anomaly (°C) for August-December 2014 (produced June 2014)

    Source: National Multi-Model Ensemble

    Figure 2.  El Nino SST anomaly (°C) identified by Johnson (2013)

    Figure 2

    Figure 2. El Nino SST anomaly (°C) identified by Johnson (2013)

    Source: Johnson (2013)

    Figure 3. Precipitation anomaly (cm) associated with El Nino during August-December

    Figure 3

    Figure 3. Precipitation anomaly (cm) associated with El Nino during August-December

    Source: Andrew Hoell, UCSB Climate Hazards Group

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