This project aims to determine the relative contribution of climate variability and human activity to streamflow decline in two river basins: the Canadian River in Texas and the Chaobai River in China. In recent decades, streamflow has been declining in both basins and the impact to regional water supplies is great. By comparing these case studies, we gain insight that supports river basin management in regions with similar problems. Watersheds, or the area of land drained by a river, are the ideal unit for water management. This study investigates how watersheds respond to different human activities and how culturally-derived management institutions influence watershed hydrology. In recent years, Chinese researchers have produced a prodigious body of work on the topic of quantifying the effects of climate variability and human activities on streamflow. There are two general approaches, both of which are adopted in this study: modeling of naturalized flows and analyses of historical trends. Naturalized flow is the amount of streamflow expected in the river in the absence of humans. Changes in naturalized flows are caused by changes in climate. Changes in observed streamflow that are not accounted for by changes in naturalized flows can then be attributed to human activity. In this way we determine the contribution of climate change and human activity, respectively, to changes in streamflow. The need to quantify hydrologic change is not unique to China or Texas, it exists all over the world. The hydrologic cycle refers to the movement of water between various pathways (precipitation, evapotranspiration, streamflow, etc.). Hydrologic change refers to changes in the hydrologic cycle. Hydrologic models are computerized representations of watersheds that simulate the hydrologic cycle. The Canadian River basin in Texas (CRB) and the Chaobai River basin in China (CBRB) are used as case studies, but the approach is applicable to other areas affected by streamflow changes. The ability to quantify and understand hydrologic change in human-impacted watersheds is essential for sustainable management of regional water resources. Studying two distinct watersheds allows us to make inferences about general hydrological relationships in human-impacted watersheds. The study also provides preliminary evidence of governmental controls on the hydrologic cycle. The Canadian and Chaobai River basins have similar drainage areas and climate. The basins also serve as the primary source of drinking water for economically important cities. The two river basins have different institutions governing land and water use. The total annual streamflows entering Miyun Reservoir in the CBRB and Lake Meredith in the CRB have decreased very significantly since the 1950s. Dramatic changes in streamflow occur immediately after the construction of large dams along the Canadian River. Precipitation has decreased slightly in the CBRB, while it has not changed significantly in the CRB. Both basins have experienced temperature increases since the 1950s. The model used to simulate naturalized flows requires precipitation, temperature, and other meteorological variables on a daily basis. Daily meteorological data in the United States is freely available and abundant; however records for individual gages are full of gaps. The evapotranspiration (ET) computer program developed for this project handles discontinuous data from multiple gages by searching on a day-by-day basis for gages with available data. The major accomplishments during the NSF East Asia and Pacific Summer Institutes (NSF-EAPSI) program include gathering all the necessary data to build models for the Canadian and Chaobai River basins, analyses of historical data for both basins, building models for the basins, and development of the ET computer program. The NSF-EAPSI program gave the authors the opportunity to use an understanding of hydrology to enhance river basin management. The case studies illustrate how hydrologic models can be used to assess and adaptively manage water resources. The project enhances collaboration between Prof. Yangâ€™s group and Prof. Caiâ€™s group, and between Tsinghua University and the University of Illinois, which will serve the global water resources community for years to come. Going forward, we plan to be actively involved in the exchange of ideas and people between these two countries thanks to the connections made through the EAPSI program. The NSF-EAPSI Program enabled the authors to conduct successful collaborative research at Tsinghua University, China during June-August 2011. The research will end with a high-quality peer-reviewed journal paper. An abstract of the paper was accepted to a major national conference. A Userâ€™s Manual regarding the preparation of input files for the hydrologic model was translated into English. To date, five presentations have been delivered to disseminate the results of this study. At the annual University of Illinois (UIUC) engineering open house in March 2012, we plan to present the basic principles of river basin management to elementary school students in an educational and entertaining manner.