This thesis examines the effect of climate and land use change on streamflow distributions in six urbanizing watersheds in the Maryland Piedmont region, and produces future predictions under three proposed scenarios of future climate and land use varying individually and then jointly. Future climate is modeled using precipitation and temperature predictions from the CCC and Hadley models. Two approaches are used to predict future streamflows: a regression model approach, and a continuous streamflow model approach. Trend tests at a 5% level of significance are used to statistically quantify emerging trends in the simulated climate and streamflow time series. Precipitation is the dominant factor and generally controls the directionality of trends in streamflows. Temperature has less influence on low flows and no apparent effect on peak flows. Land use change has caused low flows to be slightly smaller and peak flows slightly larger, but no significant trends were detected.