10.4122/1.1000001205 Matheussen, B. V. Thorolfsson, S. T. Lettenmaier, D. P. Seasonal flood frequency analysis based on disaggregated urban runoff data DTU Library, Technical University of Denmark (DTU) 2005 Urban drainage snow hydrology bootstrap resample modelling design criteria Norwegian University of Science and Technology, Dep. of Hydraulic and Environmental Eng. and SINTEF Energy Research Norwegian University of Science and Technology, Dep. of Hydraulic and Environmental Engineering University of Washington en Conference presentation 10.4122/1.1000001206 text/xml 1 Current design procedures for urban drainage systems are based on the assumption that it is short duration summer rainfall that produces the highest annual runoff peaks. Despite this several researchers report that in cold climates urban flooding may also happen as a consequence of rain in combination with snowmelt. Because of this we chose to question the assumption of rainfall being the only factor controlling urban flooding in cold climates like in Trondheim, Norway. Through a combination of hydrological modelling and a temporal disaggregation method a time series of hourly runoff data (1946-2003) are generated for the Risvollan urban catchment in Trondheim, Norway. The hourly runoff data are then used to generate flood frequency curves (FFC) for the whole year and the summer (May-Oct) period only. The results showed that a FFC based on hourly urban runoff data for the whole year has a higher 10 year flood than a FFC generated from only summer data. This implies that urban drainage design methods used for cold climates, similar to Trondheim, should consider all seasons in the design procedure.