Biomass burning-agriculture coupling in the Orinoco savannas—Particulate matter emission scenarios

Abstract

The Colombian Orinoco savannas (254 thousand km2), also known as Orinoquia or Llanos, have been steadily transformed into pastures for more than a century, and since the 1990s, into commodity crop intensified production. The cropland area expanded at 12% yr−1 during the 2007–2018 period (65% larger than in 1996–2007). Yet, we estimate that cattle ranching occupied ten times more area (34%) than cropland (3.2%) in 2018. The rest of Orinoquia, including indigenous reservations and protected areas, was in a semi-natural state, although also exposed to seasonal fire. The three main crops, oil palm, corn, and rice (72% of the sown area in 2017), accounted for 68% of the expansion, with permanent crops expanding two times faster (18% yr−1) than short-cycle crops. An extrapolation of trends indicates that the cultivated area will double by 2040 (reaching 20 thousand km2), with oil palm as the dominant crop. Satellite measurements show that 7% of Orinoquia burned every year during the 1997–2016 period, yet with large spatial and interannual variations (±26%), and significant decrease trends (up to −4% yr−1). Up to 40% of the burned area (BA) interannual variability was linked to irregular rainfall and drought. The areas with the larger fractional BA were also those with the least fractional cropland cover. A model developed to describe this coupling, along with rainfall and other effects, successfully explained most of Orinoquia’s BA variability (r2 = 0.93). The fitted model indicates that each sown hectare reduced the BA by 0.17 ha. This model predicts that the combination of cropland expansion and independent BA decline will lead to a fourfold reduction of Orinoquia’s BA by 2040 referred to 1997. Orinoquia’s crop production generated 3 Gg of PM10 (particulate matter <10 µm) in 2016, mostly from short-cycle crops, while biomass burning generated 57 Gg, i.e., 95% of the combined emissions. These are expected to halve during the 2017–2040 period, despite an 83% increase in crop production emissions, as total and seasonal emissions will remain controlled by biomass burning. Such a large pollution burden reduction should have tremendous positive impacts on public health in Orinoquia and the Andes.