Abstract:
The Soil Conservation Service Curve Number (SCS-CN) method developed by the
USDA-Soil Conservation Service (SCS, 1972) is widely used for the estimation of direct
runoff for a given rainfall event from small agricultural watersheds. The initial soil moisture
plays an important role in re-structuring of the SCS-CN method and enables us to prevent
unreasonable sudden jump in runoff estimation and this has prompted the concept of soil
moisture accounting (SMA) procedure to develop improved SCS-CN based models. Applying
the concept of SMA procedure and changed parameterization, Michel et al. Water Resour Res
41(2):1–6 (2005) developed an improved SCS-CN model (MSCS-CN), which could be
thought of an improvement over the existing SCS-CN method; however, their model still
inherits several conceptual limitations and inconsistencies. Therefore, in this study an attempt
is made to propose an improved SMA based SCS-CN-inspired model (MMSCS-CN) model
incorporating a continuous function for initial soil moisture and test its suitability over the
MSCS-CN and SCS-CN model using a large dataset from US watersheds. Using, Nash and
Sutcliffe efficiency (NSE) and root mean square error (RMSE) of these models, the overall
performance is further evaluated using rank grading system, and it is found that the MMSCSCN
scores highest mark (95; overall rank I) followed by MSCS-CN with 61 (overall rank II),
and SCS-CN model with 51 mark (overall rank III) out of the maximum 105. This study shows that the proposed MMSCS-CN model has several advantages and performs better than the
MSCS-CN and the existing SCS-CN model.
