Collaborative Research: RUI: Recovery trajectories of the hillslope green water cycle after rapidly repeated wildfires

随着气温上升，降雨和降雪变得更加间歇性，预计森林地区的野火复发率将会增加。虽然在过去的30年里，在很短的时间（10年）后重新烧毁一个地区的野火异常常见，但控制这些野火的机制是什么呢？快速复燃?都没有被完全理解。可能是森林山坡上可用水量的减少，即水文循环的改变，正在改变火灾后对植物再生的控制，以及随后的野火。然而，关于火灾后植物所需的土壤水资源、火灾后多年来被烧毁地区土壤水分的时空变化以及植被再生过程中水分反馈的数据几乎没有。这项研究解决了再燃烧后山坡水文和生态水文系统随时间恢复数据的这一关键空白，也将有助于确定再燃烧是否可能减轻或加剧下游洪水和滑坡风险，这些风险通常伴随着火灾后水流的增加。这项研究产生的新知识将与联邦和州的水和森林管理人员密切协调，包括一系列研究-管理讲习班，以改善与管理做法的研究交流。该项目还将通过一个与实地相关的志愿者组织与非营利社区建立联系，并通过在当地博物馆举办临时科学展览与公众建立联系，并在“与科学家见面”期间在当地幼儿园和小学进行便携式教育。访问和将扩大研究的机会，为本科生和研究生的研究人员。本研究旨在了解(1)山坡水文响应随自然燃烧次数的增加和自上次火灾以来的时间变化；(2)坡面土壤水分和蒸散通量的恢复与植被恢复之间的模式和反馈关系，以及它们随复烧次数、种源距离和火灾后时间的变化规律；(3)在气候变化的影响下，火灾或再燃烧后山坡水平衡的逐渐变化与下游河流流动动力学的关系。本研究将测试一个总体假设的多个组成部分，即存在时空（相关）和生物物理（因果），将土壤湿度和土壤水力过程变化联系起来。此外，它还讨论了植被再生如何为随后的火灾提供燃料负荷，以及在多次野火后下游流量和洪水风险如何随着时间的推移而消退。在另外两个季节的初步数据的基础上，将绘制6个0.25公顷现场的土壤湿度、基质电位、质地、防水性、渗透和水力特性测量、活植被和木质碎屑的地图，并在整个研究过程中进行监测。现场方法包括原位传感器和数据记录仪，土壤湿度的三维地球物理调查，微气象监测和详细的植被生态调查，包括树苗的存在和生存。位于西澳亚当斯山南侧的6个示范性野外站点具有相似的生态、气候、坡度、海拔、地形、与未燃烧森林的距离和过去每次火灾的严重程度，但在过去火灾的次数（过去13年为1至3次，未燃烧对照）和火灾发生时间上存在差异。利用遥感数据和长期的气候、干旱和河流时间序列，对主要植被和裸地覆盖类别进行蒸散发建模，并在时空上广泛地应用于两个相关流域。该模型分析旨在更好地理解不同野火再燃次数和不同恢复间隔后山坡水循环的时空动态及其与河流动力学的关系。

As temperatures rise and rain and snowfall become more intermittent, wildfire recurrence is expected to increase in forested areas. Although wildfires that re-burn an area after only a short time (10 years) have been unusually common over the last 30 years, the mechanisms governing these ?rapid reburns? are incompletely understood. It may be that decreasing water availability, i.e., an altered hydrological cycle, on forested hillslopes is changing the controls on plant regrowth after fire, and so on subsequent wildfires. However, there are almost no data on the soil water resources that plants need following fires, the spatial and temporal changes in soil moisture in burned areas over multiple years after fires, or moisture feedbacks with vegetation regrowth. This research addresses this critical gap in data on post-reburn hillslope hydrology and ecohydrologic system recovery over time and will also help identify whether reburns might mitigate or worsen the downstream flood and landslide risks that often accompany higher post-fire water flows. The new knowledge generated by this research will be produced in close coordination with federal and state water and forest managers, including a series of research-management workshops to improve research communication with management practices. The project will also engage with the nonprofit community via a volunteer organization related to the field area and with the public via creation of a temporary science exhibit for display at a local museum and also for portable education at local preschools and elementary schools during ?meet-a-scientist? visits and will expand research a opportunities for undergraduate and graduate researchers.This research aims to understand (1) how hillslope hydrological response differ with increasing numbers of natural reburns and with time since last fire; (2) how the patterns and feedbacks between the recovery of hillslope soil moisture and evapotranspiration fluxes are linked to the recovery of vegetation, and how they vary with number of reburns, seed-source distances, and time since fire; and (3) how the gradual change in the hillslope water balance relates to downstream river flow dynamics after a fire or reburn under variable climate influence. This research will test multiple components of an overarching hypothesis that there are both spatio-temporal (correlative) and biophysical (causative), linking soil moisture and soil hydraulic process changes following reburns. In addition, it addresses how the vegetation regrowth provides the fuel load for subsequent fires, and how downstream flows and flood risks recede over time following multiple wildfires. Soil moisture, matric potential, texture, water repellency, infiltration, and hydraulic property measurements, live vegetation, and woody debris will be mapped across six 0.25 ha field sites and monitored over time throughout the study, building on an additional two seasons of preliminary data. Field methods include in situ sensors and data loggers, 3D geophysical surveys of soil moisture, micrometeorological monitoring, and detailed vegetation ecology surveys including tree seedling presence and survival. The six exemplary field sites on the southern flank of Mt. Adams, WA, are of similar ecology, climate, slope, elevation, aspect, distance to unburned forest, and past severity per fire, but differ in the number of past fires (1 to 3 in the last 13 years, and an unburned control) and time since fire. Modeling of evapotranspiration will be conducted for major vegetation and bare land cover classes and applied in a spatially and temporally extensive manner across two relevant watersheds with the aid of remote sensing data and long-term climate, drought, and streamflow time-series. This modeling analysis will seek to better understand the spatiotemporal dynamics of the post-fire hillslope water cycle and its relation to streamflow dynamics after different numbers of wildfire reburns and different recovery intervals after fire.