Smoke emissions from agricultural fires in Mexico and Central America

Blanca Ríos, Graciela Binimelis de Raga

Autores: Blanca Rios and Graciela B. Raga*

* Departamento de Ciencias Atmosféricas | Interacción Micro y Mesoescala

Abstract

A

gricultural burning in Mexico and Central America is a common practice to remove crop residues. Characterization of the spatial and temporal distribution of burning emissions is essential to evaluate their environmental impacts. For this reason, smoke emissions from agricultural fires were calculated using two methods: direct and indirect. The direct method calculates the rate of smoke emission by multiplying the smoke emission coefficient by the fire radiative energy (FRE) release rate. The smoke emission coefficient was calculated from satellite measurements of aerosol optical depth and FRE made by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. The indirect method calculates the rate of smoke emissions by using FRE observations from MODIS to parameterize a diurnal fire cycle based on a Gaussian equation for each ecoregion. Fire emission estimates from each of these methods were compared with each other and with the Global Fire Emissions Database, version 4.1. A total of 482,506 and 233,660 fire pixels were detected by MODIS from 2003 to 2014 in Mexico and Central America, respectively. Active fires concentrate in the tropical forests with maximum frequencies from March to May. Agricultural fires account for 40% of total detected burns from 2003 to 2014. Considerable interannual variability is observed, with 2003, 2005, and 2011 the most active years and 2008 and 2014 the least active years. Our calculations show that agricultural smoke emissions estimated by the indirect method are lower than those estimated by the direct method by a factor of 1.4 to 4, depending on the ecoregion, although the total smoke emissions are similar between both methods. Finally, average annual smoke emissions in Mexico are the greatest in tropical humid forests and least in tropical dry forests, whereas in Central America, average annual smoke emissions are very similar for both humid and dry tropical forests.