Fire Activity and Fuel Consumption Dynamics in Sub-Saharan Africa
Fire Activity and Fuel Consumption Dynamics in Sub-Saharan Africa
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DOI：
10.3390/rs10101591
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发表时间：
2018-10
期刊：
影响因子：
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通讯作者：
G. Roberts;M. Wooster;Weidong Xu;Jiangping He
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作者：
G. Roberts;M. Wooster;Weidong Xu;Jiangping He
非洲景观火灾具有广泛性、周期性和时效性。它们烧毁了非洲大陆的大片地区，改变了陆地表面的特性，并对大气产生了重大影响。卫星对地观测数据在捕捉非洲生物质燃烧的时空变异性方面发挥了关键作用，并提供了编制火灾排放清单所需的关键数据。火焰辐射功率的主动火焰观测已证明与生物质燃烧速率呈线性关系(kg S−1)。气象卫星FRP像素产品由欧洲气象卫星组织陆地表面分析卫星应用设施(LSA SAF)近乎实时地提供，绘制了分辨率为3公里、间隔15分钟的FRP地图，这些数据可追溯到2004年。在这里，我们使用这些信息来评估整个撒哈拉以南非洲地区火灾活动的时空变化，并确定年度火灾活动和燃料消耗减少的总体趋势，这与广泛使用的基于燃烧面积测量的全球火灾排放数据库(GFEDv4)是一致的。我们首次全面评估了每次着火燃料消耗(Tg干物质，DM)和时间积分中分辨率成像光谱仪(MODIS)净光合作用(Tg，可转换为火灾前燃料负荷估计值)之间的关系。我们在非洲南半球发现了很强的线性关系(平均r=0.96)，这种线性关系部分依赖于生物群，尽管由浮游植物衍生的燃料消耗远低于由累积的PSN得出的燃料消耗，单位面积的平均燃料消耗为0.14 kg DM m−2。在北半球，由浮游植物衍生的燃料消耗也低得多，且具有较弱的线性关系(平均r=0.76)。MOD17产品在北非上空使用的生物群查询表(BLOT)的参数化差异可能是原因，但需要进一步的研究来协调这些差异。非洲南半球火灾FRE和火灾前燃料负荷之间的密切关系令人鼓舞，并突出了地球静止玻璃钢反演在提供与燃料消耗和火灾排放变化密切相关的度量方面的价值。估计燃料消耗量只占可用燃料的一小部分，这一事实表明，旋转增强型可见光和红外成像仪低估了燃料消耗量，和/或需要调整0.37兆焦耳千克−1的燃料消耗量换算系数以适用于增强型可见光和红外成像仪。未来的地球静止成像传感器，例如即将到来的第三代气象卫星(MTG)，将通过其探测比目前的第二代气象卫星更小、寿命更短的火灾的能力来减少这种低估的影响。
African landscape fires are widespread, recurrent and temporally dynamic. They burn large areas of the continent, modifying land surface properties and significantly affect the atmosphere. Satellite Earth Observation (EO) data play a pivotal role in capturing the spatial and temporal variability of African biomass burning, and provide the key data required to develop fire emissions inventories. Active fire observations of fire radiative power (FRP, MW) have been shown to be linearly related to rates of biomass combustion (kg s−1). The Meteosat FRP-PIXEL product, delivered in near real-time by the EUMETSAT Land Surface Analysis Satellite Applications Facility (LSA SAF), maps FRP at 3 km resolution and 15-min intervals and these data extend back to 2004. Here we use this information to assess spatio-temporal variations in fire activity across sub-Saharan Africa, and identify an overall trend of decreasing annual fire activity and fuel consumption, agreeing with the widely-used Global Fire Emissions Database (GFEDv4) based on burned area measures. We provide the first comprehensive assessment of relationships between per-fire FRE-derived fuel consumption (Tg dry matter, DM) and temporally integrated Moderate Resolution Imaging Spectroradiometer (MODIS) net photosynthesis (PSN) (Tg, which can be converted into pre-fire fuel load estimates). We find very strong linear relationships over southern hemisphere Africa (mean r = 0.96) that are partly biome dependent, though the FRE-derived fuel consumptions are far lower than those derived from the accumulated PSN, with mean fuel consumptions per unit area calculated as 0.14 kg DM m−2. In the northern hemisphere, FRE-derived fuel consumption is also far lower and characterized by a weaker linear relationship (mean r = 0.76). Differences in the parameterization of the biome look up table (BLUT) used by the MOD17 product over Northern Africa may be responsible but further research is required to reconcile these differences. The strong relationship between fire FRE and pre-fire fuel load in southern hemisphere Africa is encouraging and highlights the value of geostationary FRP retrievals in providing a metric that relates very well to fuel consumption and fire emission variations. The fact that the estimated fuel consumed is only a small fraction of the fuel available suggests underestimation of FRE by Spinning Enhanced Visible and Infrared Imager (SEVIRI) and/or that the FRE-to-fuel consumption conversion factor of 0.37 MJ kg−1 needs to be adjusted for application to SEVIRI. Future geostationary imaging sensors, such as on the forthcoming Meteosat Third Generation (MTG), will reduce the impact of this underestimation through its ability to detect even smaller and shorter-lived fires than can the current second generation Meteosat.