Fire-precipitation interactions amplify the quasi-biennial variability of fires over southern Mexico and Central America

Abstract. Fires have great ecological, social, and economic impacts. However, fire prediction and management remain a challenge due to a limited understanding of their role in the Earth system. Fires over southern Mexico and Central America (SMCA) are a good example, which greatly impact local air quality and regional climate. Here we report that the spring-peak (Apr–May) fire activities in this region have a distinct quasi-biennial signal based on multiple satellite datasets measuring different fire characteristics. The variability is initially driven by the quasi-biennial variations of precipitation. Composite analysis indicates that strong fire years correspond to suppressed ascending motions and weakened precipitation over the SMCA. The anomalous precipitation over the SMCA is further found to be mostly related to the East Pacific-North Pacific (EP-NP) pattern two months previous to the fire season. The positive phase of EP-NP leads to enhanced precipitation over the eastern US yet suppressed precipitation over SMCA, similar to the spatial pattern of precipitation difference between strong and weak fire years. Meanwhile, the quasi-biennial signals in precipitation and fires appear to be amplified by their interactions through a positive feedback loop on short timescales. Model simulations show that in strong fire years, more aerosol particles are released and transported downstream over the Gulf of Mexico and the eastern US, where suspended light-absorbing aerosols warm the atmosphere and cause ascending motions of the air aloft. Subsequently, a compensating downward motion is formed over the fire source region and ultimately suppresses precipitation and intensifies fires. Statistical analysis shows the different duration of the two-way interaction, where the fire suppression effect by precipitation lasts for more than 20 days, while fire leads to a decrease in precipitation at shorter time scales (3–5 days). This study demonstrates the importance of fire-climate interactions in shaping the fire activities on interannual scale and highlights how precipitation-fire interactions at short timescales contribute to the interannual variability of both fire and precipitation.