Soil Conservation Service Curve Number (SCS-CN) Method Current Applications, Remaining Challenges, and Future Perspectives

Dear Colleagues,

Predicting runoff in ungauged or poorly gauged watersheds is one of the key problems in applied hydrology. Thus, simple methods for runoff estimation are particularly important in hydrologic applications, such as flood design or water balance calculation models. Probably, the most well-documented and, at the same time, simple conceptual method for predicting runoff is the Soil Conservation Service curve number (SCS-CN) method. This method was originally developed by the U.S. Department of Agriculture, Soil Conservation Service to predict direct runoff volumes for given rainfall events and mainly for the evaluation of storm runoff in small agricultural watersheds. It was first published in 1956 in the National Engineering Handbook Section 4—Hydrology. Due to its simplicity and its extensive documentation, it soon became one of the most popular techniques among engineers and practitioners and is widely used in many hydrological applications. The main reasons are that it is a very simple but well-established method, it features easy to obtain and well-documented environmental inputs, and it accounts for many of the factors affecting runoff generation, incorporating them in a single CN parameter. The SCS-CN method has been adopted for various regions and for various land uses and climatic conditions. Furthermore, beyond its original scope for the evaluation of storm runoff, it has become an integral part of more complex, long-term watershed models. Nevertheless, the method is receiving ever-increasing attention in the hydrologic literature, with many contributions that enhance the current understanding and widen even further its range of applicability.

However, after many years of constant development and research, critical issues are still remaining, such as the following:

• Improving the SCS-CN method runoff predictions and at the same time preserving its current level of simplicity;
• Moving towards a unique generally accepted procedure for CN determination from rainfall runoff data and consideration of spatial variability in CN estimation;
• Investigation of the gains and the implications of altered initial abstraction ratios;
• Investigation of the scale dependency of CN values (Are CNs obtained at different scales (plot scale, catchment scale, etc.) compatible?);
• Investigating the implications of using SCS-CN in continuous hydrological models. Implementation of various soil moisture accounting systems and CN;
• Extending and adopting the existing CN documentation in a broader range of regions, land uses, and climatic conditions;
• Utilizing novel modeling, geoinformation systems, and remote sensing techniques to improve the method’s performance and efficiency.

Accordingly, the aim of this Special Issue is to present the latest developments in 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 remaining challenges.

Dr. Konstantinos Soulis
Guest Editor

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