我国东南沿海森林小流域径流对林火干扰的响应

The importance of fire disturbance to the watershed hydrological process has been widely known around the world. However, there is lack of systematic and in-depth discussion on the mechanism of hydrological effect of forest fire. In addition, due to huge spatial heterogeneity of forest fire, the effect of forest fire on runoff is difficult to be accurately and reliably simulated. In this study, a systematic study on the response of runoff to forest fire was implemented in a small forest watershed located at Xixi watershed within Jinjiang River basin. Firstly, the relationship between fire severity and runoff was preliminarily analyzed through fire severity investigation and runoff monitoring. Secondly, the relationship between fire severity and normalized combustion ratio was established to obtain the spatial and temporal distribution information of fire severity. Then, the runoff under fire disturbance was simulated by using the distributed hydrological model HSPF: Based on the sensitivity analysis, the model parameters were calibrated and verified, and the model parameters of land covers including burned area were all obtained. Comparing the simulation results of two watershed hydrological models (HSPF) with forest fire disturbance and without considering fire disturbance (assuming no fire), the effect of forest fire disturbance on runoff was ultimately evaluated. Finally, a statistical analysis method was used to reveal the mechanism of the hydrological process influencing by forest fire: What is the relative importance of fire disturbance to runoff change? What are the relative contributions of different fire disturbance variables to runoff change? Our study is expected to help further study the effect of fire disturbance on runoff and its mechanism.

林火干扰对流域水文过程的重要性已为国内外所认识。然而，对于林火水文过程效应的机制仍欠缺全面深入的讨论，同时由于林火的巨大空间异质性，林火对径流的影响难以准确可靠模拟。本研究以晋江西溪的森林小流域为例，开展流域径流对林火干扰响应的系统研究。首先，通过火烈度调查和径流监测，初步分析火烈度和径流之间的关系；其次，建立火烈度与归一化燃烧比的关系，获取火烈度时空分布；接着，选用分布式水文模型HSPF对林火干扰下的径流进行模拟：在灵敏度分析的基础上，率定和验证模型参数，获取包括火烧迹地在内的土地覆盖的模型参数，对比考虑林火干扰和未考虑林火干扰（假设没发生火灾）的两个水文模型HSPF的模拟结果，评估林火干扰对径流的影响；最后，采用统计分析方法，揭示林火水文过程变化的机制：林火干扰对径流变化的相对重要性？不同林火干扰变量对径流变化的相对贡献大小？本研究的开展有助于林火干扰的流域水文效应及其机制的深入研究。

林火干扰对流域水文过程的重要性已为国内外所认识。然而，对于林火水文过程效应的机制仍欠缺全面深入的讨论，同时由于林火的巨大空间异质性，林火对径流的影响难以准确可靠模拟。本研究以晋江西溪森林小流域为例，开展了流域径流对林火干扰响应的系统研究。通过对基于归一化燃烧比指数的火烈度时空分布的分析发现，该地区火烧迹地恢复易受气候变化的影响，是一个长期的过程，这将对流域径流产生深远的影响。研究结果表明，火烈度和径流之间存在密切联系，林火干扰会导致径流的增加。在参数敏感和不确定性分析的基础上，对模型参数进行了率定和验证，构建了可准确刻画林火干扰对晋江西溪流域森林小流域径流影响的流域动态模型HSPF，获取了包括火烧迹地在内的土地覆盖的模型参数。分析了考虑林火干扰和未考虑林火干扰的两个水文模型HSPF的模拟结果，结果表明林火干扰对径流增加有着极为明显的影响。在火后恢复早期，林火干扰对径流变化的重要性要高于气候因素，而在火后恢复中期，气候因素对径流变化的贡献略高于林火干扰。森林火烧迹地对径流变异的影响要大于草地火烧迹地。林火干扰对径流变异的影响，与火烈度结构有关，火烈度等级是主导因素。本研究阐释了我国东南沿海森林小流域径流对林火干扰的响应机制，研究结果丰富了我国东南沿海湿润区火后恢复的知识，增进了对林火干扰水文效应的认识。