El Niño Southern Oscillation (ENSO) impacts in Central America-El Salvador
Central America (C.A.) is home to many biodiversity hot spots and over 50 million people. This study will take an in depth look at El Salvador temperature and precipitation records during different phases of El Niño-Southern Oscillation(ENSO). The first goal is to review the available literature on drivers of climate variability in El Salvador, including topographic features and ocean/atmosphere interactions. The second goal is to investigate the potential role of climate change in El Salvador, and its implications for humans/biodiversity with repeated events such as floods, landslides and drought. The third goal of this study is to analyze available data and quantify the effects of ENSO on climate in El Salvador. The study includes a review and comparison of two climate model predictions for Central America. The results of this research confirm that ENSO has an effect on the regional climate of El Salvador. Some of the results were consistent with past studies, such as increased surface air temperatures during El Niño, while others were counter to past studies, such as precipitation during La Niña. El Salvador receives less rain during ENSO periods than during neutral years. Better climate observation and improved modeling will assist in mitigating disasters in the future.
The climatology of Central America is the result of complex interactions between the surrounding oceans and natural cyclical events. It is important to understand because it is home to over 17,000 plant species and many biodiversity hotspots (Dow and Downing, 2006). The Central American isthmus and the Caribbean Islands are home to over 50 million people (Karnauskas and Busalacchi, 2008). The purpose of this study is to review available literature on climate in Central America with an emphasis on El Salvador, investigate the potential role of climate change in the area, and use the available data to quantify the effects of El Niño-Southern Oscillation (ENSO) in El Salvador. Central America, as defined by the United Nations geo scheme, includes the following countries: Belize, Mexico, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica and Panama (www.unstats.un.org). Within Central America, El Salvador is a part of the Pacific ring of fire and is home to over 20 volcanoes (Hall and Brignoli, 2003), which further contribute to topographic and climatological variations.
The climate of El Salvador is influenced by sea surface temperatures (SSTs) (Ose and Arakawa, 2011), northeast trade winds (Hall and Brignoli, 2003), and the Intertropical Convergence Zone (ITCZ) (Haggerty, 1988). The mountainous regions within the country such as the Sierra Madre de Chiapas and Cordillera Alotepeque-Metapan also have influence over the regional climate. The combination of high relief and abundant moisture availability creates ecosystems with high biodiversity, which are particularly sensitive to changing climate and El Niño – Southern Oscillation (ENSO) (Karmalkar et al., 2011).
Relatively little research has focused specifically on the climate of Central America and the impacts of ENSO, even less exists on the direct regional impact on El Salvador (Hernandez et al., 2006). This region has experienced negative environmental impacts in the last 50 years due to climate change (Flannery, 2005), deforestation (Hernandez et al., 2006), and major climatic events such as hurricanes (Emanuel, 2005). The United Nations and the World Health Organization (WHO) have found that some of the most devastating climatic events are associated with ENSO, such as hurricane Stan which severely affected El Salvador in 2005 in the form of lingering torrential rain (Verner, 2010).
Figure .Political map of Central America showing the location of El Salvador along the Pacific Coast (source: www.lonelyplanet.com)
Figure .Map of El Salvador showing departments (source: www.geology.com)
El Niño Southern Oscillation is a natural phenomenon that occurs every 3 to 7 years and is reflected in SSTs in the equatorial Pacific Ocean. El Niño is characterized by unusually warm SSTs and La Niña is characterized by unusually cool SSTs. For ENSO monitoring, the National Oceanic and Atmospheric Administration (NOAA) uses SSTs in the Niño 3.4 region (120W to 170W longitude and 5S to 5N latitude). El Niño, also known as the warm phase, occurs when the 3-month mean SST anomaly in the Niño 3.4 region exceeds +0.5oC. La Niña, also known as the cold phase, occurs when the 3-month mean SST anomaly in the Niño 3.4 region exceeds -0.5oC. When the SSTs are not consistent with El Niño or La Niña, conditions are said to be neutral (www.cpc.ncep.noaa.gov).
ENSO has a near simultaneous effect on Central American temperature and precipitation (Karmalkar, 2011). In general during the warm phase of ENSO (El Niño) positive surface air temperature anomalies and negative precipitation anomalies are observed over Central America. Respectively during the cold phase of ENSO (La Niña) negative surface air temperatures are recorded and positive precipitation anomalies are observed over the same region (Nagura et al., 2007).
1.2. Human impact
El Salvador is the most densely populated country in the region with over 6 million inhabitants and serves as the 3rd largest economy in Central America (www.cia.gov). El Salvador is vulnerable to tropical storms, hurricanes, seismic and volcanic activity (Hall and Brignoli, 2003). One of the major consequences of extreme climatic events, especially hurricanes, is spread of disease at accelerated rates. According to the World Health Organization, over 2,500 cases of cholera were reported in 1998 in the Central American Region; approximately half of these cases were reported after Hurricane Mitch struck in October of 1998 (www.paho.org).
The World Health Organization has identified three areas of serious concern regarding climate variability and disease in Central America. The first is the increase of vector borne diseases such as malaria, dengue and yellow fever. The second is water borne diseases like cholera and diarrheal diseases such as E. coli contaminations. The third is malnutrition which is coupled with weather disasters, diarrhea, waterborne illnesses and threatened food supplies due to drought or flooding (Andersen et al., 2010). Other dangers to human health include cardio respiratory diseases brought on by increased temperatures which can increase particulate matter, pollen and ozone in the atmosphere, urban areas are exposed to heat island effects which increase mortality and morbidity especially among the homeless, elderly and poor who lack the means to take evasive action (Verner, 2010). This research paper is focused on the direct social and physical effects of ENSO on El Salvador using local station data, climate models, as well as other factors that make El Salvador a high risk natural disaster area.
2.1. Climatology and Physical Geography
The Central American region experiences two distinct seasons: a wet winter season from May through October and a dry summer season from November to April (Portig, 1965). The area also presents a bimodal annual cycle of precipitation which means that precipitation reaches a peak in June then it decreases in July and August, it reaches a second peak in September or October (Mangaña, 1999). The ministry of environment and natural resources of El Salvador (Ministerio de Medio Ambiente y Recursos Naturales www.snet.gob.sv) divides the country into three separate thermal zones based on elevation. The three thermal zones range from 28oC in the coastal plains to as low as 10oC in the highest altitudes. Physical drivers of climate in El Salvador are the northeast trade winds during the dry summer season and the northward movement of the ITCZ which creates a low pressure system off the Pacific coast bringing rain in the winter (Haggerty, 1988). During the dry season the high altitudes receive the majority of their moisture through orographic cloud formation which creates cloud forests along the Honduran border as well as a small region in the center of the country. The persistent cloud cover provides precipitation in the dry season and is an important part of the regional hydrologic cycle (Hall and Brignoli, 2003). Recent increases in temperature indicate the dry season is becoming drier and the moisture that comes in the form of orographic precipitation coupled with increasing temperatures creates drought-like conditions (Karmalkar, 2011). This subtropical region experiences strong wind gusts from the northern Polar Regions of North America. The air is warmed as it passes over the Gulf of Mexico on its way to Central America, made possible because of the North American mountain ranges that create a passage way for the air to travel south (Hall and Brignoli, 2003).
2.2. Climatic events in the last 30 years
Latin America and the Caribbean are among the regions of the world most prone to climate related hazards (Rossing and Rubin, 2010). Hurricane Mitch 1998 claimed approximately 11,000 lives and is the strongest October Atlantic hurricane on record (Emanuel, 2005), and it is associated with the 1997-1998 El Niño event and the subsequent La Niña (Verner, 2010). In El Salvador, Hurricane Mitch was responsible for 240 deaths, massive flooding, mudslides, loss of crops, and the spread of disease (WHO, 1998). In this event, El Salvador had 8 cases of cholera reported, however neighboring countries like Guatemala had over 1,100 cases and 33 deaths from cholera reported after Mitch (WHO, 1998). Presence of disease in neighboring countries make it clear that the country is susceptible to widespread outbreaks, a susceptibility that may be increased by climate change (Verner, 2010).
According to a United Nations Joint Agency Appeal in October of 2005 a series of disastrous events triggered the country of El Salvador into a state of emergency. A volcanic eruption (October 1) followed by torrential rains which were remnants of Hurricanes Rita and Stan (October 3, 4) wiped out much of that year’s coffee harvest, brought on over 700 mudslides and forced over 54,000 people to evacuate their homes. The country also experienced a 6.2 magnitude earthquake (October 7) that same week (UN Joint Report, 2005). It is also noteworthy to observe that in this search no scholarly journals were found that discussed the disease epidemics or the negative effects of ENSO in El Salvador. Only the United Nations and the World Health Organization had reports that were available for analysis.
The most recent climatic disaster struck El Salvador in October of 2011. A United Nations emergency appeal reported that tropical depression 12E (www.nasa.gov) caused heavy rains in Central America for 10 days affecting over 1.2 million people and killing 100 in the region. In El Salvador 30 deaths were reported due to landslides, 56,000 people were displaced in need of food, clean water and sanitation (www.un.org). The UN office for the coordination of human affairs (OCHA) reported an increase in flood related illnesses such as diarrhea, conjunctivitis, chicken pox and dengue. Over 69% of the country experienced flood damaged roads and infrastructure hampering access to remote areas. The agency also expressed concern for food security since the region was already experiencing high food prices before the floods which will only be exacerbated by crop losses (OCHA, 2011). The Office of Civil Protection reported on October 21, 2011 tropical depression 12E caused the overflow of 132 rivers, 419 landslides, 185 floods, 18 cases of subsidence and 20 sunken areas (www.ifrc.org).
Another main concern regarding rising global temperatures and climate variability is maintaining biodiversity in certain areas that are declared as hot spots such as parts of Central America and South America where decline of amphibian populations is strong (Karmalkar et al., 2011). In Costa Rica the Golden Toad became the first species to be declared victim of global warming and climate change (Flannery, 2005). The extinction of the Golden Toad coincided with an exceptionally dry interval caused by the 1986-1987 El Niño. Pounds et al. (2006) argued that the extinction of the Golden Toad was due to the chytrid fungus that thrived as a result of changes in climate. The available data did not support the hypothesis that climate change alone could drive the spread of pathogens, and therefore this theory was later dismissed (Lips et al., 2008). The Golden Toad relies on the mist that comes in form of orographic precipitation in order to survive. The 1986-1987 El Niño created a warmer setting in which the high clouds of Monteverde, Costa Rica remained mistless and led to the extinction of the Golden Toad, the exact cause however was not discovered until 1999 (Flannery, 2005). El Salvador is home to 87 plants and animals that are considered endangered species IUCN (Glenn, 2006) potential changes in climate could drive some species to extinction.
2.3. Climate model projections of global warming and ENSO
Several studies have been performed to assess the reliability of climate models to project future temperature and precipitation in Central America (Karmalkar et al., 2011; Hernandez et al., 2006). One study compares the Global Climate Model (GCM) (known as a multi data set: MMD) against a regional climate model called PRECIS (Providing Regional Climates for Impacts Studies)and found that the GCM severely underestimated precipitation with predictions off by over 30% in some instances (Karmalkar et al., 2011). Overall the models both struggled in simulating ENSO and disagreed on its future behavior. One main conclusion of this study that both models agreed on are the IPCC (2007) projections regarding overall temperature and precipitation. Both models indicate that most of the Central American region will experience drier conditions in the future as the global temperatures increase.
3.1 Analysis of temperature and precipitation of El Niño vs. La Niña events
El Salvador has 6 weather stations that collect temperature and precipitation data. The station in the nation’s capital of San Salvador has the longest record available. For that reason the San Salvador station data was used for this study. The first weather station began to take readings in 1956.
Figure .Time series of maximum and minimum temperature (Tmax, Tmin), dew point temperature (Tdew) and precipitation at San Salvador from 1956-2010.
There is a large gap of missing records from approximately 1967 through 1973, again from 1986 to 1994 (Figure 3); both of these periods were times of political unrest and civil war. The data that was recorded from 1956 to 1967 included maximum/minimum temperatures and dew point temperature. Precipitation data was not collected until 1974. In addition to the years of data that are missing mentioned above, there is no precipitation data from 2005 to 2010. The data used for this research to calculate monthly averages was based on each month having more than 75% of the day recorded for that month.
To better understand the effects of ENSO in El Salvador, the San Salvador station data were analyzed in the context of the NOAA ENSO data. First, we compared mean maximum temperature fluctuations during the three ENSO phases (El Niño, La Niña, and neutral) (Figure 4).
Figure .Monthly mean maximum temperature (Tmax) at San Salvador for El Niño (red), La Niña (blue) and neutral (black) years.
The final data analyzed for this study are average monthly precipitation totals. The station in El Salvador that provided these readings is approximately 30 miles inland from the Pacific Ocean. Given the topographic variation in the region, the relationships depicted might vary among regions of El Salvador.
Figure 5.Monthly mean precipitation (PRCP) at San Salvador for El Niño (red), La Niña (blue) and neutral (black) years.
4. Results and discussion
Based on the information that we have it is clear that El Niño is associated with higher than average (Tmax) surface air temperatures. ENSO does not seem to be associated with large variations in minimum temperature averages (Tmin) or dew point temperature averages (Tdew) (not shown). El Niño is associated with lower than average rainfall during the wet season. La Niña is also associated with lower rainfall (in relation to the neutral phase) to a lesser extent. La Niña years also have lower than average surface air temperatures, this anomaly corresponds to trends observed in the region in the past (Ose and Arakawa, 2011). Of the missing data, precipitation is extremely valuable and lacking the most. With a more complete record, the relationship between ENSO phases and precipitation extremes could be better defined. The increased surface air temperatures recorded in El Salvador during El Niño years correlate with the El Niño trends observed in other regions (Karnauskas and Busalacchi, 2009).This implies that El Salvador is at higher risk of waterborne disease outbreaks such as diarrhea and cholera in hot weather, these diseases are highly sensitive to changes in climate (Verner, 2010). Extreme weather events such as floods and heavy rains increase the incidence of waterborne diseases, after the 1997-98 ENSO event, a time series analysis showed an 8% increase in admissions due to diarrhea for each 1oC increase in temperature in the Central American region (WHO 2003). Rising temperatures may lengthen the season, or alter the geographical distribution of waterborne diseases, much of the protozoa viruses and bacteria that cause them thrive in warm water and weather (Andersen et al., 2011).
El Niño years leave behind a pattern of disease. Following the 1997-98 El Niño a great spike occurred in the cases of both malaria and dengue fever. After the 2002-03 El Niño, the number of dengue cases reached record levels in Central America; dengue has the most severe impacts in children ages 5-9 (Verner, 2010). The torrential rains of October 2011 do coincide with a La Niña event. In 2011 NOAA marked the August, September, October season as the first La Niña anomaly of the late year (www.cpc.ncep.noaa.gov). We cannot say definitively that La Niña is responsible of the extreme weather of October 2011, but with better monitoring, we could look for trends in the ENSO phenomenon that could help governments and NGO’s prepare for catastrophes.
In order to protect the people and environment of El Salvador resources need to be allocated for better monitoring of weather and climate in the country. Using data from a single station is limiting because it cannot represent all the variations that occur in a country that ranges from 0m at sea level to 2,700m in elevation (www.snet.gob.sv). While ENSO appears to have an effect of rainfall reduction in El Salvador, the neutral climate experiences higher rainfall levels that are sometimes associated with hurricane activity in the Atlantic such as hurricanes Rita and Stan in 2005, which was a neutral ENSO year.
The probability of disease spreading at elevated rates is higher during periods of above average precipitation and climatic distress combined with rising global temperatures (Verner, 2010). El Salvador is home to over 300 rivers many of which are prone to flooding (Haggerty, 1988). Prolonged precipitation is a large factor responsible for land/mudslides in many regions of El Salvador and other parts of Central America. On September 19, 1982 after a receiving 223mm of rain in 2 days the land on the slopes of the San Salvador volcano began to move, a mass of an estimated 220,000dropped on to the capital city in a neighborhood called Montebello killing 500 and leaving 2,400 homeless(CEPRODE, 1994). The 1982 event was during an El Niño year, based on our research the precipitation was not at higher than normal level however it was 3 months after a 7.3 magnitude earthquake which is said to have created cracks in the slopes (Bommer et al., 2011). It is also noteworthy to point out that all climatic data for 1982 and much of 1983 is missing, possibly due to the earthquake and landslide catastrophes that occurred at that time, once again this displays the crucial need for good climatic record keeping in the country. El Salvador faces higher risks overall due to the level of seismic activity, after prolonged rains the soil is loose and easily shaken by strong earthquakes. The soil is also loose in many regions due to deforestation which began in the 1960’s at a high rate and peaked in the early 1990’s leaving behind only2- 5% of natural forest standing in the country (Hetcht, 2005). The United Nations reported in 2008 that 14% of the land in the El Salvador is forest; this implies that the reforestation efforts being put in place are slowly working (http://data.un.org) (Hetcht, 2005).
Each El Niño and La Niña event has a different impact and duration, along with other factors that interact with the climate of Central America and El Salvador. An improvement in climate data collection for the region is crucial in order to protect the people. Safety and preparedness will be a major result of continuing to research the vulnerability of the region. It would be helpful to continue this research and connect climatic records with ENSO records for the entire 7 Central American countries in order to have a better understanding of how ENSO affects the area. Another coupling of information could include the interaction of the Indo Pacific Warm Pool with ENSO in relation to impacts. It is important to evaluate dangers/risk based on the factors that are present in the area: climate variability, seismic/volcanic activity, hurricanes and deforestation which put people, plants and animals in danger. When governments and local authorities use the information that is known about climatic trends for disaster mitigation, climate science can help save lives.
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