We present a multimodel analysis for mechanistic hypothesis testing in landscape evolution theory. The study site is a watershed with well‐constrained initial and boundary conditions in which a river network locally incised 50 m over the last 13 ka. We calibrate and validate a set of 37 landscape evolution models designed to hierarchically test elements of complexity from four categories: hillslope processes, channel processes, surface hydrology, and representation of geologic materials. Comparison of each model to a base model, which uses stream power channel incision, uniform lithology, hillslope transport by linear diffusion, and surface water discharge proportional to drainage area, serves as a formal test of which elements of complexity improve model performance. Model fit is assessed using an objective function based on a direct difference between observed and simulated modern topography. A hybrid optimization scheme identifies optimal parameters and uncertainty. Multimodel analysis determines which elements of complexity improve simulation performance. Validation tests which model improvements persist when models are applied to an independent watershed. The three most important model elements are (1) spatial variation in lithology (differentiation between shale and glacial till), (2) a fluvial erosion threshold, and (3) a nonlinear relationship between slope and hillslope sediment flux. Due to nonlinear interactions between model elements, some process representations (e.g., nonlinear hillslopes) only become important when paired with the inclusion of other processes (e.g., erosion thresholds). This emphasizes the need for caution in identifying the minimally sufficient process set. Our approach provides a general framework for hypothesis testing in landscape evolution.

中文翻译：

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用于景观演化模型过程表示的反向地形：2.校准和验证

我们提出了景观演化理论中的机械假设检验的多模型分析。研究地点是一个初始条件和边界条件都受到严格限制的分水岭，其中一个河网在最近的13 ka内局部切开了50 m。我们校准并验证了一组37种景观演化模型，旨在对四个类别的复杂性要素进行分层测试：山坡过程，河道过程，地表水文学和地质材料的表示形式。将每个模型与基本模型进行比较，该模型使用水流动力通道切口，均匀岩性，通过线性扩散进行的山坡运输以及与排水面积成比例的地表水排放，这是对复杂性哪些要素可以改善模型性能的正式测试。基于观察和模拟的现代地形之间的直接差异，使用目标函数评估模型拟合。混合优化方案可确定最佳参数和不确定性。多模型分析确定哪些复杂性元素可以提高仿真性能。将模型应用于独立的分水岭时，可以持续进行模型改进的验证测试。三个最重要的模型元素是：（1）岩性的空间变化（页岩和冰川分界之间的差异），（2）河流侵蚀阈值，以及（3）坡度和山坡沉积物通量之间的非线性关系。由于模型元素之间的非线性相互作用，某些过程表示形式（例如，非线性山坡）仅在与其他过程的包含（例如，侵蚀阈值）配对时才变得重要。这强调了在确定最低限度的过程集时需要谨慎。我们的方法为景观演化中的假设检验提供了一个通用框架。