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ABSTRACT , . Ii Sensible responses to natural hazards should encompass the comple- mentary elements of likelihood and severity. Flood hazard evaluation accomplishes this by relating frequency of occurrence to magnitude with the methods of flood frequency analysis. The use of these methods in current engineering and planning practice is based on the implicit ~ NO!.J! sumption that the lOO-year floodplain is fixed in areal extent. and once delineated, it will not be affected by future urbanization of the water- shed. To the extent that floodplains are dynamic, however, nonstructural management strategies such as the National Flood Insurance Program can- not be expected to fulfill their objectives. Research during the past three years has shown that this assumption of static floodplains is un- justified in southeastern New England where the hydrologic response of watersheds to extensive urban growth is conditioned by geologic, pedo- logic and morphometric parameters. Data from 18 watersheds located in ~ eastern Massachusetts and Rhode Island are used to develop a methodology whereby the change in discharge corresponding to both one and two per- cent annual exceedance probabilities may be predicted. A group of secon- dary data sources, including topographic maps, surficial geologic quad- rangles and land use maps, are employed to develop indices of urban land use change, surficial watershed properties and drainage network configuration. The dependent variable is derived from two separate es- timates of flood expectancy which are found by standard analyses of non- overlapping segments of a basin's hydrologic record. It is expressed as the ratio of change in the 50-year or IOO-year flood expectancy to the iii