Background Extreme rainstorms in Binzhou city, Shaanxi province on July 29, 2023 resulted in severe damage to the terraces in the study area. The objective of this study is to estimate the damage of terraced fields in Binzhou city, Shaanxi province, caused by heavy rainfall. This will reveal the factors that contribute to the erosion of terraced fields and provide a foundation for the future control of soil erosion in the event of extreme rainstorms.

Methods The terraced fields damaged by the rainstorm in July 2023 in Binzhou county were taken as a case example, and the volume of destruction was quantified using the volumetric method by combining field investigation with unmanned aerial vehicle imagery. Evaluation indicators such as damaged length ratio and damage point density were established, and erosion intensity was assessed using unified soil density parameters. A calculation method for evaluating terrace erosion damage under rainstorm conditions was proposed. Additionally, an analysis of the erosion characteristics of terraced fields and their influencing factors was conducted.

Results 1) The shapes of terrace slope damage were classified into five types: ellipsoidal (E), cylindrical (Cy), conical (Co), stepped (S), and combined, based on the shapes after erosion, and the calculation formulas for each type were provided one by one. 2) The shapes of damaged terraced fields in the small watershed included five types of slope damage and two types of field surface damage. Among them, there were 133 erosion investigation sites, with slope damage being the main type, and the E being the most common. The average soil erosion intensity of the terraced fields reached 10448.63 t/km², and extremely severe erosion and severe erosion were mainly concentrated in the lower slope positions, accounting for 24.00% of the total area of the terraced fields. 3) The density of damage points in the terraces was mainly concentrated in the range of 2–6 points/km, with a cumulative frequency of 43.22%. Similarly, the percentage of damage length was mainly concentrated in the range of 0 to 4%, with a cumulative frequency of 45.93%. Furthermore, the length of E damage was primarily concentrated within the range of 2 to 8 m, with a cumulative frequency of 68%. 4) The erosion of field with astragalus planting was predominantly characterized by moderate, extremely strong and severe erosion, whereas field with maize planting exhibited a prevalence of strong and greater erosion. Within each sub-area, the cumulative erosion volume exhibits a good power-function relationship with the height proportion, and there is also a more evident correlation with the catchment area.

Conclusions Overall, the mean erosion intensity of terraces subjected to extreme rainfall in Binzhou county, Shaanxi province, reached an extent of extremely strong erosion. It is recommended to adopt drainage measures for horizontal terraces in the future. Therefore, the results may provide a scientific reference for the optimization of the design and construction of terraced fields in the Loess Plateau.