AbstractEphemeral gully erosion is a significant form of soil erosion that visibly impacts soil productivity and restricts land use. While watersheds are fundamental for controlling soil erosion, past studies have focused on individual ephemeral gully or slope types, which do not fully represent changes in ephemeral gullies at the watershed scale. This research used remote sensing images (0.5 m resolution), unmanned aerial vehicles (UAV), and field investigations to analyze the spatial–temporal evolution and development rate of ephemeral gully erosion at the watershed scale on the Loess Plateau from 2009 to 2021. Using spatial information and morphological parameters of ephemeral gullies obtained from the SegNet model, we found that: (1) ephemeral gully numbers decreased from 4495 in 1999 to 2312 in 2021 due to improved vegetation coverage; (2) average growth rates of ephemeral gully frequency, length, density, dissection degree, and width were 2.87 km−2 year−1, 1.66 m year−1, 0.12 km km−2 year−1, 0.01% year−1, and 0.04 m year−1, respectively; (3) ephemeral gully erosion volume (V) and length (L) had a good power function relationship: . The root‐mean‐square error (RMSE) and coefficient of determination (R2) between measured and predicted ephemeral gully volumes indicated that the V–L relationship has a good predictive ability for ephemeral gully volume; thus, the V–L model was used to evaluate the development rate of ephemeral gully erosion volume in small watersheds from 2009 to 2021, revealing an average value of 743.20 m3 year−1. This study presents an empirical model for assessing ephemeral gully volume and volume changes at a watershed scale using high‐resolution remote sensing images, providing a reference for understanding the development of ephemeral gully erosion in small watersheds over time.