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Abstract:Soil moisture conditions prior to input design storms need to be known in the planning and design of urban stormwater control facilities using the design storm approach. Limited information is available on these soil moisture conditions which are commonly referred to as the antecedent soil moisture conditions. In this study, a deterministic continuous simulation model was used to simulate antecedent soil moisture conditions under south-western Ontario, Canada, climate conditions. A wide range of different soil types were investigated and various statistical analyses on the simulated antecedent soil moisture results were performed. Frequency analyses illustrated typical distributions of antecedent soil moisture conditions and the influence of finer and coarser textured soil particles. Empirical equations were developed for the estimation of average antecedent soil moisture conditions based on commonly known soil characteristics. Satisfactory performance of the empirical equations was demonstrated by comparing between field average antecedent soil moisture data and empirically estimated average antecedent soil moisture values. These equations are therefore recommended for use in urban stormwater studies incorporating the design storm approach.

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ABSTRACT. Using the past 45 years of climate data in south-western Ontario, Canada and a deterministic continuous simulation model, this study investigates the long-term variability in rain-fed soil moisture in urban areas as influenced by climate change. Statistical analyses of four variables, i.e., soil moisture, precipitation, temperature and evapotranspiration were carried out. As found from other studies for other locations, these analyses confirm increasing temperatures and average growing season precipitation in south-western Ontario. Results show that both overall soil moisture and evapotranspiration have increased throughout the 45-year period. The probability/frequency distributions of soil moisture were obtained and the analysis shows an increasing average growing season soil moisture availability from the 1960's to the 1990's. The direct influence of precipitation and temperature on soil moisture and evapotranspiration were examined, revealing a stronger relationship of soil moisture and evapotranspiration with precipitation rather than temperature. Overall increasing average growing season soil moistures have very likely resulted from overall increasing rainfall during the growing seasons in south-western Ontario.

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