Relative Importance of Input Parameters in the Modeling of Soil Moisture Dynamics of Small Urban Areas

Continuous-simulation water balance models may be used to study the soil moisture dynamics of small urban areas. These models require as input many soil-texture and land-use-related parameters. Difficulties encountered in determining the values of these input parameters warrant an investigation on their relative importance. In this study, a series of global sensitivity analyses were performed to evaluate the response of selected outputs from a continuous-simulation soil moisture model to variations of specified input parameters. Using randomly generated input parameter values representing various site conditions, the soil moisture model was run with meteorological data from Toronto, Ontario, Canada. Three output statistics, namely, average soil moisture, the standard deviation, and skewness of the output daily soil moisture distributions, were determined from each model run. Four types of sensitivity indices between the output statistics and the input parameters were calculated. Based on these sensitivity indices, it was concluded that the wilting and hygroscopic-point soil moisture levels and the soil moisture level below which plants start to endure water stress are the most important input parameters for all three output statistics. The relative importance of soil’s porosity, saturated conductivity, and the runoff curve number of the study area becomes greater and almost reaches the same level as the most important parameters when the skewness of the output daily soil moisture distributions is the output statistic of interest.