Severe fires associated to climate change and land cover changes are becoming more frequent in Mediterranean Europe. The influence of environmental drivers on fire severity, especially under different environmental conditions is still not fully understood. In this study we aim to determine the main environmental variables that control fire severity in large fires (>500 ha) occurring in fire-prone ecosystems under two different environmental conditions following a transition (Mediterranean-Oceanic)-Mediterranean climatic gradient within the Iberian Peninsula, and to provide management recommendations to mitigate fire damage. We estimated fire severity as the differenced Normalized Burn Ratio, through images obtained from Landsat 8 OLI. We also examined the relative influence of pre-fire vegetation structure (vegetation composition and configuration), pre-fire weather conditions, fire history and topography on fire severity using Random Forest machine learning algorithms. The results indicated that the severity of fires occurring along the transition (Mediterranean-Oceanic)-Mediterranean climatic gradient was primarily controlled by pre-fire vegetation composition. Nevertheless, the effect of vegetation composition was strongly dependent on interactions with fire recurrence and pre-fire vegetation structural configuration. The relationship between fire severity, weather and topographic predictors was not consistent among fires occurring in the Mediterranean-Oceanic transition and Mediterranean sites. In the Mediterranean-Oceanic transition site, fire severity was determined by weather conditions (i.e., summer cumulative rainfall), rather than being associated to topography, suggesting that the control exerted by topography may be overwhelmed by weather controls. Conversely, results showed that topography only had a major effect on fire severity in the Mediterranean site. The results of this study highlight the need to prioritise fuel treatments aiming at breaking fuel continuity and reducing fuel loads as an effective management strategy to mitigate fire damage in areas of high fire recurrence.

在地中海欧洲，与气候变化和土地覆盖变化相关的严重火灾正变得越来越频繁。仍然没有完全了解环境驱动因素对火灾严重性的影响，尤其是在不同环境条件下。在本研究中，我们旨在确定在伊比利亚半岛内（地中海-大洋洲）-地中海气候梯度过渡后两种不同环境条件下易发火的生态系统中发生大火（> 500公顷）时控制大火严重程度的主要环境变量，并提供管理建议以减轻火灾损失。通过从Landsat 8 OLI获得的图像，我们将火灾严重程度估计为差异化的归一化燃烧率。我们还使用随机森林机器学习算法检查了火灾前植被结构（植被组成和配置），火灾前天气状况，火灾历史和地形对火灾严重性的相对影响。结果表明，沿过渡带（地中海-海洋）-地中海气候梯度发生的火灾的严重性主要受火灾前植被组成的控制。然而，植被组成的影响在很大程度上取决于与火灾复发和火灾前植被结构形态的相互作用。在地中海-海洋过渡和地中海地区发生的火灾之间，火灾严重性，天气和地形预测因子之间的关系不一致。在地中海-大洋过渡地带，火灾的严重程度是由天气条件（即夏季累积降雨）确定的，而不是与地形相关联的，这表明由地形控制的作用可能会被天气控制所淹没。相反，结果表明，地形仅对地中海地区的火灾严重性有重大影响。这项研究的结果强调，需要优先处理旨在打破燃料连续性和减少燃料负荷的燃料处理方法，以此作为减轻高发火地区火灾损失的有效管理策略。