Assessing controls on hydrologic connectivity

Degradation of drylands impacts 40% of Earth’s land surface and is responsible for up to 25% of global greenhouse gas emissions. Many dry ecosystems are sustained by runoff-runon processes that result in the transport of resources, particularly water, from bare to vegetated sites, determining the availability of water to plants. Such transport is dependent on storm and site characteristics, making its behavior temporally dynamic and spatially complex. We used tray experiments to reveal patterns of connectivity and water availability to vegetation using a well-characterized dryland soil data from the Lehavim LTER in Israel. Results showed that these imaging techniques are able to capture differences in flow patterns arising across soil surfaces with varying slope, roughness, and spatial variation in infiltration properties. Several spatial indices characterizing overland flow patterns were found to correlate with runoff volume. The presence of high permeability soil patches substantially regulated overland flow. The research presents a new approach for high fidelity predicting runoff based on emulation of a coupled Saint Venant equation‐Richards equation model with random forest regression. The spatial pattern features that explain most of the hydrological variability are not stable across different soils, slopes, and storms, potentially explaining some of the difficulties associated with direct use of spatial metrics for predicting landscape function. Although the current emulator relies on strong assumptions, including smooth topography, binary permeability fields, and only a small collection of soils, slope, and storm scenarios, it offers a promising way forward for applications in dryland and urban settings and in supporting the development of potential connectivity indices.