SWAT Literature Database for Peer-Reviewed Journal Articles

Title:Statistical procedures for evaluating daily and monthly hydrologic model predictions 
Authors:Coffey, M.E., S.R. Workman, J.L. Taraba and A.W. Fogle 
Journal:Transactions of the ASAE 
Volume (Issue):47(1) 
Article ID: 
URL (non-DOI journals): 
Broad Application Category:hydrologic only 
Primary Application Category:calibration, sensitivity, and/or uncertainty analysis 
Secondary Application Category:karst effects 
Watershed Description:5.5 km^2 Univ. of Kentucky ARC site, located located near the city of Versailles in central Kentucky, U.S. 
Calibration Summary:daily 1995 r2 & E = .26 & .09 daily 1996 r2 & E = .40 & .15 monthly 1995 r2 & E = .70 & .41 monthly 1996 r2 & E = .88 & .61 
Validation Summary: 
General Comments:Watershed was characterized by Karst features such as sinkholes and springs. Over 15 different statistical tests were used to evaluate SWAT output vs. measured data. Some of the tests were not applicable for the daily comparisons. The daily results showed "good model fit" but improvements were noted to be needed in the simulated timing, peak flows, & recession curve predictions. The monthly estimates were closer to meeting the required statistical assumptions. 
Abstract:The overall study objective was to evaluate the applicability of different qualitative and quantitative methods for comparing daily and monthly SWAT computer model hydrologic streamflow predictions to observed data, and to recommend statistical methods for use in future model evaluations. Statistical methods were tested using daily streamflows and monthly equivalent runoff depths. The statistical techniques included linear regression, Nash-Sutcliffe efficiency, nonparametric tests, t-test, objective functions, autocorrelation, and cross-correlation. None of the methods specifically applied to the non-normal distribution and dependence between data points for the daily predicted and observed data. Of the tested methods, median objective functions, sign test, autocorrelation, and cross-correlation were most applicable for the daily data. The robust coefficient of determination (CD*) and robust modeling efficiency (EF*) objective functions were the preferred methods for daily model results due to the ease of comparing these values with a fixed ideal reference value of one. Predicted and observed monthly totals were more normally distributed, and there was less dependence between individual monthly totals than was observed for the corresponding predicted and observed daily values. More statistical methods were available for comparing SWAT model-predicted and observed monthly totals. The 1995 monthly SWAT model predictions and observed data had a regression Rr 2 of 0.70, a Nash-Sutcliffe efficiency of 0.41, and the t-test failed to reject the equal data means hypothesis. The Nash-Sutcliffe coefficient and the Rr 2 coefficient were the preferred methods for monthly results due to the ability to compare these coefficients to a set ideal value of one. 
Keywords:Dependent data, Hydrologic time series, Hypothesis testing, Model validity, Non-normality