Projet de recherche :
Potential relationship between forest fire emission and fire severity
Wildtires have huge impacts on both atmosphere and ecosystem (Bergeron and Gauthiers, 2017) as substantial vegetation being removed and large amounts of aerosol and trace gases being released into the atmosphere (Crutzen et al., 1990; Andreae et al., 2001). As two important tire regime parameters, satellite retrieved tire intensity and tire severity show huge potential applications in assessing the tire impacts on atmosphere and ecosystem.
For tire intensity, it can be directly obtained from satellite products. Previous works (lchoku and Ellison, 2014; Mebust et al., 2011) have applied the tire intensity parameter tire radiative power (FRP) to estimate emission coefficients (mass released per unit energy, g/MJ) of aerosol and nitrogen oxides.
For fire severity, it can be quantitied by the differenced Normalized Burn Ratios (dNBR), which is calculated using the change of reflectance of the NIR (near infrared) and MIR (middle infrared) bands between pre-fire and post-fire im.ages (Key and Benson, 2006). lts validation has been valued by Soverel et al. (2010) and Boucher et al. (2017). What's more, it has been applied to estimate the carbon emission (Rogers et al., 2014) and study the proportion of different burn-severity classes across forest composition and structure types (Meigs et al., 2018).
However, such kinds of studies are few. More investigations are needed to apply the tire intensity and fire severity to fire emission estimation, and to study the fire severity impacts on post-fire surface characteristics especially under the context of climate change.
Therefore, my thesis will be preliminarily entitled as: Using remote sensing to assess effects of tire severity on air quality and post fire ground conditions which will include 3 chapters (papers):
1) Evaluation of atmospheric aerosol and trace gas production according to tire intensity/fires severity, fuel type and forest types;
Fire radiative power and dNBR will be used to estimate the aerosol productions. The microwave index EDVI will be applied to assess the effect of vegetation water content on the fire intensity/fire severity and aerosol emissions .
2) Explore the effect of the fire severity on post fire ground characteristics;
This study will focus on the changes of surface albedo, the post-fire evaporation transpiration(ET) process, and the post-fire leaf area coverage.
3) Analyze the impacts of current and future climate on fire severity and radiative forcing.
This part will focus on the role of precipitation/drought and temperature on the fire severity. Further, the radiative forcing introduced will be studied through the pathways of changing surface albedo and the radiation transfer process in the atmosphere."
Yuyun Fu, Rui Li, Yves Bergeron, Raphaël Chavardes, Jiheng Hu, Yipu Wang, Jiawei Duan, Dong Li, Yuanxi Cheng, Osvaldo Valeria. Assessing forest fire properties in Northeastern Asia and Southern China with satellite microwave Emissivity Difference Vegetation Index (EDVI). 2022. ISPRS Journal of Photogrammetry and Remote Sensing 183:54-65
DOI : 10.1016/j.isprsjprs.2021.10.019
In the context of global warming, forest fires are expected to occur more frequently and intensively, and impose more significant impacts on human society, terrestrial ecosystems, and atmosphere. Most of the existing methods in monitoring large-scale forest fire are based either on satellite visible and infrared observations or weather-based indices. This work explored the advantages of a new satellite microwave-based vegetation index in monitoring forest fire occurrence and fire intensity in Northeastern Asia and Southern China. Specifically, we used satellite observations during 2002–2011 to investigate the correlation at different temporal scales between forest fire properties (fire count, FC; fire radiative power, FRP) and the vegetation water content proxy of the Microwave Emissivity Difference Vegetation Index (EDVI) derived from the Moderate Resolution Imaging Spectroradiometer and the Advanced Microwave Scanning Radiometer-EOS on Aqua satellite. The correlations were compared to that with three weather-based indices including the Fine Fuel Moisture Code, Initial Spread Index and Fire Weather Index (FWI) to determine whether EDVI provides new independent information of forest fires. Finally, EDVI and the weather-based indices FWI were combined to establish multivariate linear regression models to estimate FC and FRP. Results show that: 1) the temporal variations of FC and total FRP are negatively correlated with EDVI using the daily and monthly observations at 1° grid and regional scales; and overall opposite annual cycles and interannual variations between FC (and total FRP) and EDVI are observed in Northeastern Asia and Southern China; 2) compared to the weather-based indices, EDVI shows higher correlation with the temperate forest fire properties in Southern China while shows weaker correlation with the forest fire properties in Northeastern Asia; and a combination of the two kind of indices is found to improve the explained variance for fire properties in both regions; 3) multivariate linear regression models based on EDVI and FWI provide better estimation of FC and FRP compared to the linear regression models based on FWI alone. To our knowledge, this is the first work that comprehensively investigates the potential application of the microwave-based vegetation water content index in forest fire count and fire intensity.
Rui Li, Yipu Wang, Jiheng Hu, Yu Wang, Qilong Min, Yves Bergeron, Zongting Gao, Jinjun Liu, Yuyun Fu, Osvaldo Valeria. Spatiotemporal Variations of Satellite Microwave Emissivity Difference Vegetation Index in China Under Clear and Cloudy Skies 2020. Ecography 7(5):e2020EA001145
DOI : 10.1029/2020EA001145
In this study, we used data from multiple sensors onboard NASA Aqua satellite to conduct a 10?year (2002–2011) remote sensing of microwave emissivity difference vegetation index (EDVI) over China. We investigated the spatial and temporal variations of EDVI in tropical and subtropical evergreen forest, deciduous forest, rice and wheat farmlands, grassland, and montane vegetation regions. The average of China's EDVI is positive in dense vegetation regions and negative in sparse vegetation regions, depending on the proportion of bare soil and open water. In all selected studying regions, the seasonal variation of EDVI follows the trend of vegetation phenology, even in regions with large proportion of open water. EDVI is positively correlated to the greenness of vegetation (normalized difference vegetation index [NDVI]) with certain phase difference in their seasonal cycle. In autumn, EDVI begins to decline earlier and faster than NDVI. In tropical rainforest, EDVI also starts to increase earlier than NDVI in spring. The large?scale spatial distribution of EDVI under clear sky and cloudy sky is similar. In montane vegetation regions, EDVI under heavy clouds (90% fraction) conditions is significantly greater than that under clear sky (10% fraction), indicating a possible cloud induced enhancement of vegetation water content. In forests and croplands in the plains, such effect is not remarkable.
Yuyun Fu, Rui Li, Yves Bergeron, Yunfei Fu, Yu Wang, Zongting Gao, Jian-Guo Huang. Satellite-Observed Impacts of Wildfires on Regional
Atmosphere Composition and the Shortwave
Radiative Forcing: A Multiple Case Study. 2018. J. Geophys. Res. 123(15): 8326-8343
DOI : 10.1029/2017JD027927
Emissions of aerosols and trace gases from wildfires and their direct shortwave radiative forcing (DSRF) at the top of atmosphere were studied using satellite observations from Moderate?Resolution Imaging Spectroradiometer, Atmospheric Infrared Sounder, Clouds and Earth Radiant Energy System on Aqua, and Ozone Monitoring Instrument on Aura. The dominant fuel types of the selected fire cases in the northeast of China (NEC), Siberia (Russia), and California (USA) are cropland, mixed forest, and needle?leaf forest, respectively. For the cropland fire case in NEC, the fire radiative power?based emission coefficients (Ce) of aerosol is 20.51 ± 2.55 g/MJ, half that of the forest fire cases in Siberia (40.01 ± 9.21 g/MJ) and California (45.23 ± 8.81 g/MJ), and the carbon monoxide (CO) Ce (23.94 ± 11.83 g/MJ) was about one third and half that of the forest fire cases in Siberia and California, respectively. However, the NOx (NO2 + NO) Ce (2.76 ± 0.25g MJ?1) of the cropland fire in NEC was nearly 3 times that of those forest fire cases. Ratios of NOx to aerosol, HCHO, and CO in the cropland case in NEC show much higher values than those in the forest fire cases. Despite the differences of the Ce and the composition ratios, the DSRF efficiency of smoke aerosol at the top of atmosphere showed similar values among those fire cases. Our results highlight the large variability of emission rate and relative chemical composition but similar DSRF efficiencies among wildfires, which would provide valuable information for understanding the impact of fire on air quality and climate.
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Yuyun Fu, Osvaldo Valeria, Rui Li, Yves Bergeron. Forest fire emission and fire severity estimation using satellite detection and modeling 21e colloque de la Chaire AFD. Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, Québec. (2019-11-30)
Yuyun Fu Estimation des émissions et de la sévérité des feux de forêt à l'aide de la détection par satellites et la modélisation. projet thèse (2019-10-25)
