“El Niño” events increase seasonal wildfire danger in Ecuador

Abstract

Weather is a key driver of catastrophic wildfire seasons. On a global scale, different phases of the El Niño-Southern Oscillation, “El Niño” or “La Niña”, modulate weather and therefore wildfire activity. Ecuador is one the most biodiverse countries in the world and wildfires produce severe impacts to its ecosystems. This investigation explores for the first time the relationship between wildfire weather and El Niño-Southern Oscillation in the tropical Andes. Wildfire weather variability has been quantified using seasonal metrics of the McArthur Forest Fire Danger Index. The calculation of this index requires weather station data that were only available since 1997. Therefore, the availability of data was extended using the Twentieth Century Reanalysis Project to cover the period 1963-2010. Bushfire weather in the seasons April-May-June and July-August-September show significant correlations with the NINO3.4 index (r=0.37,p=0.003, n=47 and r=0.4, p=0.001, n=47 respectively). Additionally, a Chi-squared test showed that every extreme wildfire season in this region was linked to an ‘El Niño’ event. Our results demonstrate that ‘El Niño” events bring hot and dry conditions conducive to wildfires in the antecedent—April-May-June—and simultaneous—July-August-September—wildfire seasons in Ecuador.

Introduction

Wildfires are a global phenomenon that produces severe impacts (Luke 1978, Conard 1997, Morton 2003). Catastrophic wildfire events claim lives (Haynes 2008, Haynes 2010), degrade the environment (Shakesby 1993, Stephens 2004, Lane 2010) and destroy building infrastructure (Morton 2003, McAneney 2009, Crompton 2010). Wildfires also contribute to biodiversity loss (Kodandapani 2008, Pastro 2011) and affect the climate (Conard 1997). They are part of the natural evolution of vegetation ecosystems (HaynesBradstock 2012). However, human actions amplify the impact over people, nature and infrastructure (Pausas 2011). In fact, wildfires have a strong anthropogenic ignition pattern. In addition, population growth in rural areas increase human vulnerability to this hazard. The threat of wildfires have encouraged extensive research on the behavior of its precursors.

Weather is one of the key components that contributes to wildfire activity (Powell 1983, Williams 1999, Mills 2005, Haines 1988, Mccaw 2007, Dowdy 2012, Engel 2013). Wildfire weather refers to the meteorological influence over wildfires over a period of time —usually within days—. Common variables associated with wildfire weather are temperature, relative humidity, wind speed and precipitation (BoM 2009). Each variable exerts influence in the liberation of water content in vegetation. This process—Evapotranspiration—controls the availability of fuels to be burnt. Most of the research conducted on wildfires and climate focuses on this daily approach (Roads 2005). Yet, the study of wildfire predictability on a seasonal scale is also important. A key factor to explore this perspective is El Niño Southern-Oscillation (ENSO) (Swetnam 1990, Simard 1985, Kitzberger 2002, Beckage 2003, Wooster 2012).

ENSO produces negative rainfall anomalies in some wildfire-prone regions (Swetnam 1990, Simard 1985, Kitzberger 2002, Beckage 2003, Wooster 2012). The intensity of these anomalies depends on the regional influence of ENSO over climate. These rainfall deficits occur over the months before—and during–the wildfire season. ENSO’s influence may even increase by the superposition of the Inter-decadal Pacific Oscillation (IPO) (Verdon 2004). ENSO also has an influence over ignition patterns. In some regions it fosters the occurrence of lightning strikes (Beckage 2003). These facts encourage the investigation of new studies of ENSO and wildfire weather around the world.

The west coast of South America is one of the regions most affected by ENSO. The coastal areas of Peru and Ecuador experience massive rainfall episodes during strong El Niño events (Rodbell 1999). Yet, there has not been enough research on its influence over other natural hazards. Wildfires occur all over South America (Manta 2008). However, studies about wildfire weather in the northern Andean region are scarce. This study aims to describe the seasonal variability of wildfire weather in Ecuador. Also, we investigate if there is a link between this type of weather and ENSO in this region. This is important because wildfires occur every year in this country producing severe impacts (Ministerio del Ambiente 2013, Secretaria de Ambiente 2013). A better understanding of wildfire weather variability and its precursors can provide useful information. These insights could be of special interest to emergency response services and planning authorities.

This article comprises six sections. In the first section we provide background and justify the importance of this study. Section two describes the Ecuadorian Andean region as our study area. Section three presents details about the datasets employed in this research. Section four explains the different methods applied. Section five shows the results of our investigation. Finally, section six presents a discussion of the results and concluding remarks.

Study area

Geography

Ecuador is located in the north-west side of South-America (see Figure 1). The country has a diverse geography. It comprises a continental territory between the latitudes 01o 28’ N and 05o 02’ S and longitudes 75o 11’ W and 81o 04’ W (Instituto Geográfico Militar (IGM) 2013). The Galapagos Islands are also part of the country. These islands are approximately 1000 Km from the continent. The national territory has a total area of 256.370 Km2 (Instituto Geográfico Militar (IGM) 2013). The Andes mountains divide the continental Ecuador into three areas: the Coast, Andean and Amazon regions. Each of these regions has diverse geographical features, climate, and ecosystems. The highlands are the most wildfire-prone region because of its specific natural characteristics.

The Andes mountains are the most important geographical feature of Ecuador—and South-America— (Insel 2010). This mountain range crosses Ecuador from North to South. The Ecuadorian Andes comprises two flanks of mountains: the eastern and western ’Cordilleras’. Between these two flanks—that include active volcanoes—there are several inter-Andean valleys. Many of these Andean plateaus are over 3000 m above sea level. The steep elevations have an important effect on local climate. The lapse rate create the conditions for different Bio-climatic zones to exit. This enhances biodiversity. Yet, the original vegetation of the Andean valleys has almost disappeared. Most of the endemic vegetation was replaced by the Australian specie Eucalyptus globulus around 1860 (Ministerio de Ambiente del Ecuador 2012). Other introduced species are the Pinus radiata (from California) and the Pinus patula (from Mexico). This occurred for commercial reasons (Anchaluisa 2013) with great ecological impact. Further, these species are prone to wildfires in the Andean dry season.

Climate

The tropical Andes climate has several drivers. The Amazon forest, oceanic currents, and the topography are among the main drivers (Martínez 2011). The Amazon forest—through Evapo-transpiration—produces a great amount of water vapor. This water precipitates along the western Cordillera because of an orographic precipitation process. This precipitation is also produced in the eastern Cordillera. Air masses advected from the Pacific Ocean produce this effect. The influence of the Pacific Ocean in the climate variability is important. The Pacific Decadal Oscillation (PDO) is the main driver of decadal climate variability in this region (Martínez 2011). On the other hand, the inter-annual variability depends on the El Niño Southern Oscillation (ENSO) (Vuille 2000, Villacis 2003, Martínez 2011). These influences create several climate regions within the Andes.

Most of the Ecuadorian Andes—between 1500 to 3000 m—have a “Semi-Humid Mesothermal” climate (Pourrut 1995). Mean temperatures in this region range from 8 oc to 20 oc. Maximum temperatures span from 22 oC and 30 oC. Minimum temperatures range from -4 oc to 5 oC. Air masses from the Pacific Ocean and the Amazon region create three seasons (Pourrut 1995). Two wet seasons during the periods February-May and October-November. A dry season spans from June to September. Total annual precipitation ranges from 800 mm to 1500 mm along the Andes. Relative humidity varies from 65 to 85 percent.

Fire

Wildfires mostly occur in three geographical regions of Ecuador. The Andean region has large extensions of introduced Eucalyptus forests (Anchaluisa 2013). Thus, the availability of fuels makes it the most wildfire-prone region. The fire season in the Ecuadorian Andes spans from July to November (Secretaria de Ambiente 2013). Yet, the most critical months are July, August and September (Estacio 2012, Secretaria de Ambiente 2013). The coast and the Galapagos Islands experience wildfire episodes from January to May