Abstract:

High temperature and drought are key climatic drivers of wildfires. Based on historical wildfire vector data from 1984 to 2023 and multi-source high-resolution climate datasets in California, USA, this study comparatively analyzes the seasonal trends of maximum temperature, maximum and minimum vapor pressure deficit, precipitation and the standardized precipitation evapotranspiration index, and their relationships with burned area in forested regions. The results show that both wildfire frequency and burned area have increased significantly over the past four decades, with summer and autumn being the main fire seasons. Wildfire activity is mainly concentrated in topographically complex and densely vegetated regions, such as the southern Transverse Ranges, the western Coast Ranges, and the northern mountainous areas. Meteorological variables exert a pronounced seasonal influence on wildfire activity, among which maximum temperature, maximum and minimum vapor pressure deficit, during summer exhibit significant positive correlations with burned area, indicating that the co-occurrence of high temperature and drought is the primary climatic driver of frequent and large-scale wildfires. Results from the random forest model further confirm that during the main wildfire seasons, maximum temperature together with maximum and minimum vapor pressure deficits play dominant roles in driving wildfire activity.

Key words: California, wildfire, drought, vapor pressure deficit, standardized precipitation evapotranspiration index, climate change

摘要：

高温和干旱是山火发生的重要气候驱动因素。本文基于1984—2023年美国加利福尼亚州山火历史矢量数据与多源高分辨率气候数据，对比分析了四季最高气温、最大（最小）饱和水汽压差、降水量及标准化降水蒸散指数的变化趋势及其与森林区过火面积的关系。结果表明，过去40 a山火发生频次和过火面积均呈明显上升趋势，夏季和秋季为主要火灾季节。山火主要集中在地形复杂、植被覆盖丰富的南部横断山脉、西部海岸山脉及北部山脉等区域。气象要素对山火的影响具有显著季节性，其中夏季最高气温、最大和最小饱和水汽压差与过火面积均呈显著正相关，表明高温和大气干燥度的协同作用是驱动山火频发与规模扩大的主要气象因素。随机森林模型的分析结果进一步证实，在主要山火发生的季节，最高气温、最大和最小饱和水汽压差均具有主导作用。

关键词: 加利福尼亚州, 山火, 干旱, 饱和水汽压差, 标准化降水蒸散指数, 气候变化