Wildfire Influence on Rainfall Chemistry and Deposition in Texas during the 2011-2014 Drought

From 2011 to 2014, one of the most severe and intense droughts in Texas recorded history led to widespread wildfires across the state, with unknown effects on atmospheric nutrient and pollutant deposition. The objectives of this research were to: (1) characterize the frequency, magnitude, and spatiotemporal distribution of Texas wildfires (2011-2014); (2) identify smoke occurrence and source regions at eight Texas National Atmospheric Deposition Program (NADP) National Trends Network (NTN) sites (2011); and (3) quantify the influence of wildfire on weekly rainwater chemistry and deposition in 2011 at three NADP sites (Sonora, LBJ Grasslands, Attwater Prairie NWR). Data on large wildfires, smoke occurrence, and rainfall chemistry and deposition were coupled with principal component and back-trajectory analysis to address these objectives. Between 2011-2014, 72% of all wildfires occurred in 2011, accounting for 90% of the total area burned. In total, there were 17 extreme wildfires (i.e., in the 95th percentile of hectares burned), of which 11 occurred in 2011. Wildfire activity was concentrated in West Texas ecoregions and consumed primarily shrub/scrub and grassland/herbaceous land cover. Although West Texas experienced the most wildfires, smoke at the NADP locations in 2011, the "high-fire year," was more frequent in East Texas due to regional wind patterns transporting smoke from diverse source locations. In 2011, weeks with smoke-influenced rain events––defined as weeks in which the rainfall event air mass trajectory intersected a smoke polygon, at any time, for at least one hour in the 72-hours prior to rainfall at the NADP site––had higher concentrations of Ca2+, Mg2+, K+, NH4+, and SO42- compared to background samples (not affected by smoke). At LBJ Grasslands, four smoke-influenced rain samples deposited >49% of annual wet deposition for all ions. Principal component analysis identified wildfire as a key component contributing to the variance in the dataset. Taken together, these findings highlight the potential atmospheric and ecosystem impacts of future megadroughts and associated wildfires on smoke occurrence and fire-related deposition in the Southern Plains region.