Ephemeral flows and vegetation productivity: Insights for desert conservation

In desert environments, infrequent but intense rainfall events drive ephemeral flows that shape the landscape, influence vegetation patterns, and sustain biodiversity. However, despite their ecological and hydrological importance, ephemeral flows are poorly mapped and assessed, hindering effective study, management, and conservation. To address this gap, we developed and validated a high-resolution surface hydrology dataset for the Borrego Springs Subbasin in California, USA, using a 1-m digital elevation model (DEM) and the ArcGIS Hydrology Toolset. The dataset includes detailed outputs illustrating water movement across the landscape, including flow direction, flow accumulation, flow networks, and distance to the nearest flow path for each cell in the subbasin. Validation was conducted using satellite imagery following a significant monsoon rainfall event, which revealed visible water flow and wet soil. Leveraging this dataset, we present a novel framework for examining the relationship between flow proximity and vegetation productivity, using the mean growing season normalized difference vegetation index (NDVI) as a proxy for vegetation productivity and cover. Our findings reveal a strong decrease in NDVI values with increasing distance from flow paths. Dense, highly productive vegetation (NDVI > 0.5) was restricted to areas within 40 m of ephemeral flow paths, while the highest NDVI (NDVI > 0.75) was confined to within 10 m. These findings underscore the central role ephemeral flows play in structuring desert vegetation by generating consistent spatial patterns of productivity at the meter scale. However, we also found that urban development in the central subbasin has significantly disrupted natural flow networks, reducing hydrologic connectivity and altering the distribution of surface water resources. When viewed in the context of finer scale soil moisture dynamics and broader geomorphic processes, these patterns offer insight into the multiscale physical drivers shaping arid landscapes. By validating the dataset and exploring its ecological applications, this study provides essential insights into the ecohydrological interactions that govern arid regions and offers a valuable tool for managing and conserving desert ecosystems.