Evaluation of three daily rainfall generation models for SWAT
The Soil and Water Assessment Tool (SWAT) is a hydrologic model that was developed to predict the long-term 
impacts of land use change on the water balance of large catchments. Stochastic models are used to generate the daily rainfall 
sequences needed to conduct long-term, continuous simulations with SWAT. The objective of this study was to evaluate the 
performances of three daily rainfall generation models. The models evaluated were the modified Daily and Monthly Mixed 
(DMMm) model, skewed normal distribution (SKWD) model and modified exponential distribution (EXPD) model. The study 
area was the Woady Yaloak River catchment (306 km2) located in southwest Victoria, Australia. The models were assessed 
on their ability to preserve annual, monthly, and daily statistical characteristics of the historical rainfall and runoff. The mean 
annual, monthly, and daily rainfall was preserved satisfactorily by the models. The DMMm model reproduced the standard 
deviation of annual and monthly rainfall better than the SKWD and EXPD models. Overall, the DMMm model performed 
marginally better than the SKWD model at reproducing the statistical characteristics of the historical rainfall record at the 
various time scales. The performance of the EXPD model was found to be inferior to the performances of the DMMm and 
SKWD models. The models reproduced the mean annual, monthly, and daily runoff relatively well, although the DMMm and 
SKWD models were found to preserve these statistics marginally better than the EXPD model. None of the models managed 
to reproduce the standard deviation of annual, monthly, and daily runoff adequately.