西南地区不同下垫面雷电活动特征与森林雷击火的关系

Relationship between characteristics of lightning activity on different underlying surface and forest lightning fire in southwest China

【目的】西南地区是我国第二大天然林区,该地生态系统脆弱,森林雷击火灾频发。通过遥感、探测资料分析不同地表覆盖类型、不同海拔下垫面的雷电活动特征,探究雷电活动对森林雷击火的影响。【方法】根据2005—2017年全球闪电定位系统(WWLLN)闪电数据、MCD12Q1土地覆盖数据、SRTM(shuttle radar topography mission)海拔数据以及相应森林雷击火个例,结合Theil-Sen趋势分析、Mann-Kendall趋势检验、相对密度差分析,对我国西南地区雷电活动随下垫面类型、海拔的变化特征及其与森林雷击火的关系进行研究。【结果】(1)2005—2017年西南地区云地闪频次以每年8.75%的速率增加。四川和云南交界的攀枝花附近区域是最高值核心区。(2)海拔500~1000 m、稀树草原类下垫面年均云地闪频次最多。以相对密度差表征雷电活跃程度,从季节上看,春季最活跃;从昼夜变化尺度上看,昼间最活跃。表现活跃的下垫面集中在海拔0~1000 m段,以及农用地/自然植被拼接、稀树草原类和城区为主的地表类型。(3)云地闪在不同下垫面均呈增长趋势,其增长面积占比为西南地区的93.48%。其中,海拔3500 m以上和草地类型下垫面的增长趋势最显著,从海拔和地表类型来看,显著的面积占比均超过80%。(4)年云地闪频次越高,发生森林雷击火的概率越大。海拔0~1000 m森林雷击火发生与云地闪活动的下垫面特点一致,海拔1000 m以上雷击火主要受高云地闪频次影响。【结论】西南地区雷电活动与下垫面的海拔、地表类型关系密切,且这一关系随不同时间尺度而变化。作为森林雷击火的起因,结合下垫面特征分析雷电活动,探究森林雷击火,可以为西南山地天然林保护提供科学支撑。

【Objective】Southwest China is the second largest natural forest region in China,where the ecosystem is fragile and forest lightning fire disasters occur frequently.According to the causal relationship between lightning and forest lightning fire,the characteristics of lightning activities on underlying surfaces with different land cover types and different altitudes,and the influence of lightning activity on forest lightning fire is explored.【Method】Based on WWLLN lightning data,land cover data MCD12Q1,altitude data SRTM and corresponding lightning forest fires from 2005 to 2017,combined with Theil-Sen trend analysis,Mann-Kendall trend test,relative density difference analysis.The variation characteristics of lightning activity with underlying surface type and altitude in southwest China and its relationship with forest lightning fire were studied.【Result】(1)From 2005 to 2017,the cloud-to-ground lightning frequency in southwest China increased at a rate of 8.75% per year.The area near Panzhihua at the border of Sichuan and Yunnan maintains the core area of the highest value in years and seasons.(2)The annual cloud-to-ground lightning frequency was the highest in the underlying surface of savanna at an altitude of 500-1000 m.The degree of lightning activity is characterized by the relative density difference.It is most active in spring and most active in daytime on a daily scale.The active surface types are concentrated in the 0-1000 m elevation,Agricultural land/natural vegetation Mosaic,savanna type and urban type.(3)Cloud-to-ground lightning showed an increasing trend in different underlying surfaces,and its area accounted for 93.48% in southwest China.Among them,the growth trend of underlying surface of above 3500 m altitude and grassland type is the most significant,and the significant area accounts for more than 80% from the elevation and surface type respectively.(4)The higher the annual cloud-to-ground lightning frequency,the greater the probability of lightning fire.The occurrence of forest lightning fire at 0-1000 m altitude is consistent with the characteristics of the underlying surface of cloud-to-ground lightning distribution,and the lightning fire above 1000 m altitude is mainly affected by high cloud-to-ground lightning frequency.【Conclusion】The lightning activity in southwest China is closely related to the underlying surface altitude and surface type,and the relationship varies with different time scales.As the cause of forest lightning fire,the analysis of lightning activity and forest lightning fire combined with the characteristics of underlying surface can provide scientific support for the protection of natural forest in southwest mountainous area.