Developing global climate anomalies suggest potential disease risks for 2006-2007

Abstract

Background: El Niño/Southern Oscillation (ENSO) related climate anomalies have been shown to have an impact on infectious disease outbreaks. The Climate Prediction Center of the National Oceanic and Atmospheric Administration (NOAA/CPC) has recently issued an unscheduled El Niño advisory, indicating that warmer than normal sea surface temperatures across the equatorial eastern Pacific may have pronounced impacts on global tropical precipitation patterns extending into the northern hemisphere particularly over North America. Building evidence of the links between ENSO driven climate anomalies and infectious diseases, particularly those transmitted by insects, can allow us to provide improved long range forecasts of an epidemic or epizootic. We describe developing climate anomalies that suggest potential disease risks using satellite generated data.

Results: Sea surface temperatures (SSTs) in the equatorial east Pacific ocean have anomalously increased significantly during July - October 2006 indicating the typical development of El Niño conditions. The persistence of these conditions will lead to extremes in global-scale climate anomalies as has been observed during similar conditions in the past. Positive Outgoing Longwave Radiation (OLR) anomalies, indicative of severe drought conditions, have been observed across all of Indonesia, Malaysia and most of the Philippines, which are usually the first areas to experience ENSO-related impacts. This dryness can be expected to continue, on average, for the remainder of 2006 continuing into the early part of 2007. During the period November 2006 - January 2007 climate forecasts indicate that there is a high probability for above normal rainfall in the central and eastern equatorial Pacific Islands, the Korean Peninsula, the U.S. Gulf Coast and Florida, northern South America and equatorial east Africa. Taking into consideration current observations and climate forecast information, indications are that the following regions are at increased risk for disease outbreaks: Indonesia, Malaysia, Thailand and most of the southeast Asia Islands for increased dengue fever transmission and increased respiratory illness; Coastal Peru, Ecuador, Venezuela, and Colombia for increased risk of malaria; Bangladesh and coastal India for elevated risk of cholera; East Africa for increased risk of a Rift Valley fever outbreak and elevated malaria; southwest USA for increased risk for hantavirus pulmonary syndrome and plague; southern California for increased West Nile virus transmission; and northeast Brazil for increased dengue fever and respiratory illness.

Conclusion: The current development of El Niño conditions has significant implications for global public health. Extremes in climate events with above normal rainfall and flooding in some regions and extended drought periods in other regions will occur. Forecasting disease is critical for timely and efficient planning of operational control programs. In this paper we describe developing global climate anomalies that suggest potential disease risks that will give decision makers additional tools to make rational judgments concerning implementation of disease prevention and mitigation strategies.

Figure 1

Sea Surface Temperature (SST) anomalies for October 2006. Above normal SSTs have developed in the equatorial eastern Pacific Ocean (~2°C) and also in the equatorial Indian Ocean (~1°C) typical of warm ENSO events. The SST anomalies are computed with respect to 1982–2006 base period means.

Figure 2

Outgoing Longwave Radiation (OLR) anomalies for October 2006. OLR anomalies are used to infer tropical precipitation. As shown here positive OLR anomalies indicate suppressed convection and very dry conditions (brown to red colors) over Western Pacific – Indonesian region and positive OLR anomalies illustrated enhanced precipitation in the central and eastern Pacific Ocean, western equatorial Indian Ocean, East Africa and across the Sahel (shown in shades of blue)

Figure 3

IRI Multi-Model Probability Forecast for Precipitation for November-January 2007, Issued September 2006.

Figure 4

OLR anomalies at the peak of the 1997/98 El Niño showing suppressed convection and drought conditions over southeast Asia, Amazonia, western Australia and enhanced convection and precipitation over central and eastern Pacific Ocean, Peru, and Eastern Africa.

Figure 5

Hotspots of potential elevated risk for disease outbreaks under El Niño conditions: 2006 – 2007.