Despite the ecological and socioeconomic impacts of wildfires, little attention has been paid to the spatiotemporal patterns of nighttime fire activity across the conterminous United States (CONUS). Daytime fire radiative power (FRP) detected by the Moderate Resolution Imaging Spectroradiometer (MODIS) was nearly evenly split (54% vs. 46%) between inside and outside wildfires from 2003 to 2020. In contrast, 94% of nighttime FRP was detected within wildfires, of which 95% was detected within large wildfires (> 2023 ha). Nighttime proportions (i.e., the proportion of total summed FRP detected by MODIS at night) were lowest (3%) outside wildfires when coincident 1000-hr fuel moistures were highest and vegetation fires were smaller and less intense. As 1000-hr fuel moistures decreased, MODIS active fire pixels shifted out of agricultural and prescribed fires and into wildfires with higher nighttime per-pixel values of FRP such that nighttime proportions peaked at 29% for the largest wildfires. Increases in nighttime proportions within larger wildfires were attributed to increases in nighttime persistence whereby under the driest conditions, daytime fire activity detected by MODIS was more likely to continue burning with sufficient vigour to be detected again at night. From 2003–2020, MODIS detected significant (p < 0.01) increasing trends in nighttime wildfire fire activity, with a +54%, +42% and +21% increase in the annual nighttime sum of FRP, annual nighttime active fire pixel counts and annual mean nighttime per-pixel values of FRP, respectively, detected in the latter half of the study period. Nighttime trends were corroborated using observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) as well annual wildfire statistics reported by U.S. federal, state and local agencies. Moreover, MODIS detected a significant positive trend in the nighttime proportion of FRP emitted from wildfires, indicating that in the absence of diurnal differences in detection biases, increases in nighttime fire activity since 2003 have outpaced daytime increases. However an analysis of MODIS omission rates revealed that increasing nighttime proportions were at least partially attributed to a relatively greater improvement in nighttime detection performance compared to the daytime for larger wildfires burning during drier conditions. Nighttime fire activity already poses additional risks to firefighters and communities, and this work suggests that projected increases in the frequency of large wildfires will be accompanied by increases in the extent and intensity of nighttime fire activity.

尽管野火对生态和社会经济产生影响，但很少有人关注美国本土 (CONUS) 夜间火灾活动的时空模式。从 2003 年到 2020 年，中分辨率成像光谱仪 (MODIS) 检测到的白天火灾辐射功率 (FRP) 在内部和外部野火之间几乎均匀分布（54% 对 46%）。相比之下，94% 的夜间 FRP 在内部检测到野火，其中 95% 是在大型野火（> 2023 公顷）中检测到的。当同时发生的 1000 小时燃料水分最高且植被火灾较小且强度较低时，夜间比例（即 MODIS 在夜间检测到的总 FRP 总和的比例）在野火之外最低 (3%)。随着 1000 小时燃料水分的减少，MODIS 活动火灾像素从农业火灾和规定火灾转移到夜间每像素 FRP 值较高的野火，使得夜间比例在最大的野火中达到 29% 的峰值。大型野火中夜间比例的增加归因于夜间持续性的增加，在最干燥的条件下，MODIS 检测到的白天火灾活动更有可能继续燃烧，并有足够的活力在夜间再次检测到。从 2003 年到 2020 年，MODIS 检测到显着（MODIS 检测到的白天火灾活动更有可能以足够的活力继续燃烧，以便在夜间再次检测到。从 2003 年到 2020 年，MODIS 检测到显着（MODIS 检测到的白天火灾活动更有可能以足够的活力继续燃烧，以便在夜间再次检测到。从 2003 年到 2020 年，MODIS 检测到显着（p  < 0.01) 夜间野火火灾活动的增加趋势，FRP 的年度夜间总和、年度夜间活动火灾像素数和 FRP 的年度平均夜间每像素值分别增加了 +54%、+42% 和 +21% ，在研究期的后半段检测到。使用可见红外成像辐射计套件 (VIIRS) 的观察结果以及美国联邦、州和地方机构报告的年度野火统计数据，证实了夜间趋势。此外，MODIS 检测到夜间野火排放的 FRP 比例呈显着正趋势，表明在检测偏差没有昼夜差异的情况下，自 2003 年以来夜间火灾活动的增加速度超过了白天的增加。然而，对 MODIS 遗漏率的分析表明，与白天在干燥条件下燃烧的较大野火相比，夜间比例的增加至少部分归因于夜间检测性能的相对更大的改进。夜间火灾活动已经给消防员和社区带来了额外的风险，这项工作表明，预计大型野火发生频率的增加将伴随着夜间火灾活动的范围和强度的增加。