Wildfire gas emission and its impact on crop yields

Abstract

Wildfire activities are more frequent due to the effects of global warming and climate change. It causes a lot of damage in terms of impact on agriculture and air quality through the emission of large amounts of trace gases and particular matters. A critical step to quantify the wildfire related air pollution impacts on crop productivity is firstly to assess the emission of primary gas- and particle-phase emissions (e.g. Carbon Monoxide (CO), nitrogen dioxide (NO₂)). Therefore, using NO₂ and CO data measured by the Tropospheric Monitoring Instrument (TROPOMI), together with fire counts and fire radiative power (FRP) from MODIS, we analyzed the temporal and spatial variation of NO₂ and CO column densities over three selected areas covering savanna and temperate forest vegetation in Australia 2019-2020 bushfires in Chapter 2. The ΔNO₂/ΔCO emission ratio and emission factor were also estimated. The ΔNO₂/ΔCO emission ratio was found to be 1.57 ± 1.71 for temperate forest fire and ranged from 2.0 ± 2.36 to 2.6 ± 1.92 for savanna fire. For savanna and temperate forest fires, satellite-derived NOx emission factors were found to be 1.48 g kg⁻¹ and 2.39 g kg⁻¹, respectively, whereas the CO emission factors are 107.39 and 126.32 g kg⁻¹, respectively. This study demonstrates that the large-scale emission ratio from the TROPOMI satellite for different biomass burnings can help identify the relative contribution of smoldering and flaming activities in a large region and their impacts on the regional atmospheric composition and air quality. Next, we estimate how air pollution from fire smoke influences soybean yield over the non-wildfire-prone Midwestern farmlands of the United States (U.S.) in Chapter 3. We develop robust statistical models, based on historical crop data, fire smoke products as well as climate data, and satellite-based ground-level fine particulate matter (PM[subscript 2.5]) pollution. We observed increased exposure to heavy smoke days during the growing season in the Midwest region, ranging from 2 to 48 days on average during 2008-2022. Relative yield change due to smoke exposure has been worsened over all states, with the largest trend in North Dakota by a rate of -1.7 % per decade and the lowest in Illinois at a rate of -0.4 % per decade. Our result confirms that a substantial decline in yield loss from PM[subscript 2.5] indicates that smoke pollution control has had widespread benefits on soybean yield. However, wildfires already affected PM[subscript 2.5] trend in the U.S. in recent years, and the trend of wildfire specific PM[subscript 2.5] reduced yield was the largest in North Dakota with a rate of 1.4 % dec⁻¹. Increasing smoke-related PM[subscript 2.5] suggests the yield gain benefiting from the Clean Air Act in the non-wildfire-prone Midwestern U.S. is declining. Our findings call for attention to yield damage from exposure to the smoke plume under climate warming-induced frequent and more severe wildfires due to fuel aridity. Last, in Chapter 4, we analyze the variation of total precipitable water and its response to temperature at the global scale, our results indicate a global increase in total precipitable water (TPW) of ~2 % per decade from 1993 to 2021. These variations in TPW reflect the interactions of global warming feedback mechanisms across different spatial scales. Our results also revealed a significant near-surface temperature (T[subscript 2m]) warming trend of ~0.15 K per decade during 1958-2021. This consistent warming at a rate of ~0.21 K per decade after 1993 corresponds to a strong water vapor response to temperature at a rate of 9.5 % K⁻¹ globally, with land areas warming approximately twice as fast as the oceans. The relationship between TPW and T[subscript 2m] showed a variation around 6 - 8% K⁻¹ in the 15-55 °N latitude band, aligning with theoretical estimates from the Clausius–Clapeyron equation.