Collaborative Research: Modeling and monitoring of landscape evolution along a climate gradient: Kohala Peninsula, Hawaii

气候，特别是降雨，是塑造景观最重要的力量之一，但量化降雨对景观发展的影响仍然是一个挑战。很容易看出干旱和湿润地形之间的差异，但事实证明，很难量化土壤发育、地表和地下水流、山坡和河流侵蚀等物理过程在这两种环境之间的差异。位于夏威夷大岛北端的Kohala半岛为解决这个问题提供了绝佳的野外环境。在大约20公里宽的半岛上，降雨量从4000毫米/年到不到200毫米/年不等。深切口的沟壑支配着半岛湿润的一面，而在干燥的一面，浅沟壑消失了，然后在整个景观中重新出现。半岛湿润的一面已经形成了深厚的土壤，风化过程非常强烈，指甲可以在许多岩石上刮出沟槽。相比之下，在干燥的一面，表面土壤通常很浅，岩石和裸露的岩石表面很少风化。该项目将通过实地监测和数值模拟，量化半岛两侧水文和侵蚀过程的差异。两个集水区，一个在干区，一个在湿区，将配备测量降雨量、山坡和沟壑的水流深度、土壤水分含量和侵蚀率的设备。这些设备将在整个项目期间持续运行。实地调查将提供对沟壑几何形状的详细观察，以及控制切割速率的变量，如沉积物粒度、岩石硬度和破裂程度。这些数据将被纳入一个数值景观演化模型。该模型将用于在景观演变的时间尺度上系统地探索关键气候控制和地表过程响应之间的反馈。现场数据将用于约束模型中的物理过程，并启发具体的建模场景。这个项目将解决一个基本的科学问题，即降雨模式如何影响风化和侵蚀的过程。地球上几乎每座山脉都有降雨梯度，这项研究的发现将对夏威夷群岛以外的地区具有广泛的意义。气候、水文和侵蚀之间的详细相互作用的知识可以应用于整个地球的景观。此外，通过量化景观发展与降雨之间的联系，可以更有效地预测潜在气候变化对景观演变的影响。该项目将开发一些数值模型，供整个科学界免费使用，以便本研究的结果可以很容易地应用于其他环境和广泛的科学问题。

Climate, and more specifically rainfall, is amongst the most important forces that shape a landscape, yet quantifying the impacts of rainfall on landscape development remains a challenge. It is easy to see the differences between the topography in arid versus humid landscapes, but it is has proven difficult to quantify how physical processes such as soil development, surface and subsurface water flow, and hillslope and fluvial erosion, differ between these two environments. The Kohala Peninsula, on the northern tip of the Big Island of Hawaii, offers an excellent field environment to address this question. Across the approximately 20 km wide peninsula, rainfall rates very from upwards of 4,000 mm/year to less than 200 mm/year. Deeply incised gulches dominate the topography of the wet side of the peninsula, while on the dry side, shallow gulches disappear and reappear across the landscape. The wet side of the peninsula has developed deep soils and the process of weathering is so intense that a fingernail can scrape a groove in many rocks. In contrast, on the dry side, surface soils are often shallow and rocky and exposed rock surfaces are much less weathered. This project will quantify the differences in hydrologic and erosion processes on the contrasting sides on the peninsula using both field monitoring and numerical modeling. Two watersheds, one on the dry side and one on the wet side, will be equipped with devices to measure rainfall rates, water flow depths on both the hillslopes and in the gulches, soil moisture content, and erosion rates. These devices will operate continually throughout the duration of the project. Field surveys will provide detailed observations of the geometry of the gulches and the variables that control incision rates, such as sediment grain size, rock hardness, and degree of fracturing. These data will be incorporated into a numerical landscape evolution model. The model will be used to systematically explore feedbacks between key climatic controls and surface process responses over the time scales at which landscapes evolve. Field data will be used to both constrain physical processes in the model and inspire the specific modeling scenarios.This project will address a fundamental scientific question of how rainfall patterns actually influence the processes of weathering and erosion. Rainfall gradients are present across almost every mountain range on Earth and the findings from this study will have broad significance beyond the Hawaiian Islands. Knowledge of the detailed interactions among climate, hydrology, and erosion can be applied to landscapes across the planet. Furthermore, by quantifying links between landscape development and rainfall, the effects of potential climate change on landscape evolution can be predicted more effectively. This project will develop a number of numerical models that will be freely available for use throughout the scientific community, so that the findings from this study can be easily applied in other settings and to a wide range of scientific questions.