中国东南海域活跃火强度时空动态与发生类型

自然和人为因素引发的植被火是全球生态系统的重要干扰因子,而基于卫星获取的活跃火（active fires）是探究人-火关系与活跃火发生机理、扩展机制的基础。相对于陆域活跃火,海上活跃火发生的时空动态及其强度、类型等研究较为薄弱。基于VIIRS活跃火和海洋地形等数据,通过分析中国东南海域活跃火发生的时间规律、强度特征、地形属性和距海岸线距离等特性,初步确定了海上活跃火类型界定体系。结果表明：① 本区相同位置活跃火发生具有时序性。2015年前后两年内相同位置活跃火逐渐减少,且低纬地区更突出;而2015年前后三年内低纬地区活跃火发生强度稳定、高纬地区逐渐减少。② 中国东南海域活跃火呈现明显的空间集-疏特征,即沿岸海域“条带状”聚集区、以曾母暗沙为中心的“团状”聚集区、南海诸岛周围的分散区。③ 2012—2013年、2015年、2020年活跃火总强度与其月均强度变化一致,即其发生强度增强归因于活跃火的面状、分散发生;2014年、2016—2019年活跃火总强度与月均强度峰值不同步,即其强度增强归因于活跃火的点状、集中发生。④ 基于时空、强度和集聚特征,结合人类活动频繁区布局,将发生时间有规律（重复）、发生空间有特征（海域深度500 m以内、距海岸线距离200~1000 m且具集聚特征（Moran's指数为0.52,P<0.00001））、强度较高的海上活跃火定义为海上人为火。

Spatio-temporal dynamics and occurrence types of active fire intensity in the southeast sea of China

Natural and/or man-made active fires are important drivers of the disturbance of global ecosystems. Compared with the ongoing research of terrestrial active fires, studies on those within the vast ocean remains relatively weak. With the Visible Infrared Imaging Radiometer Suite (VIIRS) 375 m active fire products (Version 1) provided by the Fire Information for Resource Management System (FIRMS) and marine topography (DEM) data, a preliminary definition system for the occurrence types of active fires at sea has been established, by analyzing the characteristics of their temporal information, intensity characteristics, topographic attributes and distance from the coastline in the southeast sea of China. The results showed that: (1) The occurrence of active fires in the study area was characterized by time-series patterns. The quantity of active fires in situ in the two years before and after 2015 gradually dwindled particularly at the lower latitudes. However, active fire intensity at lower latitudes kept stable, while it declined in higher latitudes during 2012-2018. (2) Active fires in the southeast sea of China showed obvious characteristics of spatial aggregation and dispersion, including a long strip accumulation belt along the coastline, a small mass accumulation area centered surrounding the Zengmu Ansha, and a relatively scattered distribution around other islands. (3) The total intensity of active fires showed consistently temporal changes in those of the average monthly intensity during 2012-2013, 2015 and 2020. The intensity enhancement was attributed to the scaled and dispersed occurrence of active fires. In contrast, the total intensity was not synchronized with the peak of the monthly average, indicating that the enhanced intensity was mainly due to either sporadic or concentrated fire occurrence. (4) With the occurrence characteristics of time and space, intensity and concentration, combined with the location information of the oil and gas wells, those occurrences with temporal repetitiveness and spatially observed at sea lower than 500 m and a distance of 200-1000 m to the coastline along with agglomeration (i.e., the Moran's index equaling to 0.52, P<0.00001), as well as higher intensity, were defined as the combustion of man-made fire at sea.