We simulated watershed hydrologic response to land use scenarios representing different sets of policies for suburban development and watershed management in an urbanizing watershed near Portland, Oregon. We asked (1) Can watershed-scale planning and development policies reduce the hydrologic impacts of urbanization? (2) How effective are different policies (including “green” neighborhood design, riparian protection, and representative Low Impact Development (LID) stormwater controls) in maintaining the pre-development hydrologic regime? and (3) Does climate change influence these results? We co-developed 50-year land and water management scenarios with a stakeholder advisory committee and used a spatially-explicit natural and human systems model to evaluate changes in water balance and streamflow characteristics under each scenario. We also used a factorial analysis to explore the influence of individual scenario elements on watershed hydrology. Results indicate that the biggest driver of change for this watershed was the spatial extent of development, followed by the nature of the development pattern, climate, forest harvest, and use of LID controls. Stormwater runoff increased as developed area increased, as did stream discharge for both periods of high and low flow. Increases in evapotranspiration (ET) with climate warming were offset by reductions in ET with development. Designs that condensed development and preserved upland and riparian forest showed the greatest potential for maintaining pre-development water balance and streamflow regimes, thereby reducing impacts of urbanization. These results bridge spatial and temporal scales important to decision-makers, highlighting the importance of considering impacts over time of neighborhood-scale development decisions on watershed-scale hydrology.

在俄勒冈州波特兰附近的城市化流域中，我们模拟了流域水文对土地利用情景的响应，这些情景代表了郊区发展和流域管理的不同政策集。我们问（1）分水岭规模的规划和发展政策能否减少城市化的水文影响？（2）在维持开发前的水文制度方面，不同的政策（包括“绿色”社区设计，河岸保护和代表性的低影响开发（LID）雨水控制）有多有效？（3）气候变化是否会影响这些结果？我们与利益相关者咨询委员会共同开发了50年的土地和水管理方案，并使用空间明晰的自然和人类系统模型来评估每种方案下水平衡和水流特征的变化。我们还使用了析因分析来探讨各个情景元素对流域水文学的影响。结果表明，该流域变化的最大驱动力是发展的空间范围，其次是发展模式的性质，气候，森林采伐和LID控制的使用。雨水径流随着开发面积的增加而增加，高流量和低流量期间的流量排放也一样。随着气候变暖，蒸散量（ET）的增加被开发中蒸散发量的减少所抵消。凝聚发展并保护高地和河岸森林的设计显示出保持发展前水平衡和水流状况的最大潜力，从而减少了城市化的影响。这些结果弥合了对决策者而言至关重要的时空尺度，