Abstract. Past and future trends in the frequency of high danger fire weather conditions have been analysed for the UK. An analysis of satellite-derived burned area data from the last 18 years has identified the seasonal cycle with a peak in spring and a secondary peak in summer, the high level of interannual variability, and the lack of a significant trend despite some large events occurring in the last few years. These results were confirmed with a longer series of fire weather indices back to 1979. The Initial Spread Index (ISI) has been used for spring, as this reflects the moisture of fine fuel surface vegetation, whereas conditions conducive to summer wildfires are hot, dry weather reflected in the moisture of deeper organic layers which is encompassed in the Fire Weather Index (FWI). Future projections are assessed using an ensemble of regional climate models from the UK Climate Projections, combining variables to derive the fire weather indices. The results show a large increase in hazardous fire weather conditions in summer. At 2 °C global warming relative to 1850–1900, the frequency of days with “very high” fire danger is projected to double compared to a recent historical period. This frequency increases by 5 times at 4 °C of global warming. Smaller increases are projected for spring, with a 150 % increase for England at 2 °C of global warming and a doubling at 4 °C. A particularly large projected increase for late summer and early autumn suggests a possible extension of the wildfire season, depending on fuel availability. These results suggest that wildfire can be considered an “emergent risk” for the UK, as past events have not had widespread major impacts, but this could change in future. The large increase in risk between the 2 °C and 4 °C levels of global warming highlights the importance of global efforts to keep warming below 2 °C.

中文翻译：

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英国火灾天气的过去和未来趋势

摘要。已经分析了英国高危火灾天气条件频率的过去和未来趋势。对过去 18 年卫星燃烧面积数据的分析确定了春季高峰和夏季次高峰的季节周期，年际变率高，尽管发生了一些大事件，但缺乏显着趋势在过去的几年中。这些结果在 1979 年的一系列火灾天气指数中得到了证实。初始蔓延指数 (ISI) 已用于春季，因为它反映了精细燃料表面植被的水分，而有利于夏季野火的条件是炎热、干燥天气反映在更深有机层的水分中，包含在火灾天气指数 (FWI) 中。使用来自英国气候预测的区域气候模型集合评估未来的预测，结合变量以推导出火灾天气指数。结果表明，夏季危险火灾天气条件大幅增加。与 1850-1900 年相比，全球变暖 2 °C 时，“非常高”火灾危险的天数预计将比最近的历史时期增加一倍。在全球变暖 4 °C 时，该频率会增加 5 倍。预计春季的增幅较小，全球变暖 2°C 时英格兰的增幅为 150%，全球变暖 4°C 时增幅将翻一番。夏末和初秋的预计增幅特别大，这表明野火季节可能会延长，具体取决于燃料供应情况。这些结果表明，野火可以被视为英国的“紧急风险”，因为过去的事件没有产生广泛的重大影响，但这在未来可能会改变。全球变暖在 2°C 和 4°C 之间的风险大幅增加，凸显了全球努力将升温控制在 2°C 以下的重要性。