The Soil Conservation Service (SCS) curve number (CN) method is one of the most popular methods for computing the runoff volume from a rainstorm. It is popular because it is simple, easy to understand and apply, and stable, and accounts for most of the runoff producing watershed characteristics, such as soil type, land use, hydrologic condition, and antecedent moisture condition. The SCS-CN method was originally developed for its use on small agricultural watersheds and has since been extended and applied to rural, forest and urban watersheds. Since the inception of the method, it has been applied to a wide range of environments. In recent years, the method has received much attention in the hydrologic literature. The SCS-CN method was first published in 1956 in Section-4 of the National Engineering Handbook of Soil Conservation Service (now called the Natural Resources Conservation Service), U. S. Department of Agriculture. The publication has since been revised several times. However, the contents of the methodology have been nonetheless more or less the same. Being an agency methodology, the method has not passed through the process of a peer review and is, in general, accepted in the form it exists. Despite several limitations of the method and even questionable credibility at times, it has been in continuous use for the simple reason that it works fairly well at the field level.

Probably, the most well-documented, and at the same time, simple conceptual method for predicting runoff depth from rainfall depth is the Soil Conservation Service curve number (SCS-CN) method. This Special Issue presents the latest developments in the SCS-CN methodology, including, but not limited to, novel applications, theoretical and conceptual studies broadening the current understanding, studies extending the method’s application in other geographical regions or other scientific fields, substantial evaluation studies, and ultimately, key advancements towards addressing the key remaining challenges, such as: improving the SCS-CN method runoff predictions without sacrificing its current level of simplicity; moving towards a unique generally accepted procedure for CN determination from rainfall-runoff data; improving the initial abstraction estimation; investigating the integration of SCS-CN method in long-term continuous hydrological models and the implementation of various soil moisture accounting systems; extending and adopting the existing CNs documentation in a broader range of regions, land uses and climatic conditions; and utilizing novel modeling, geoinformation systems, and remote sensing techniques to improve the performance and the efficiency of the method.

This history of the Department of Agriculture's Soil Conservation Service traces the agency's development and expansion and describes its activities over the past thirty to forty years.