Abstract: Cities in the world’s developing countries are experiencing dramatic growth. The United Nations estimates the world’s urban population will increase from about half to nearly 60% of the world’s population within just two decades. This growth is stressing the ability of resource infrastructure needed to support that growth. Despite the extension of improved water supplies to more than a billion urban residents over the past two decades, the development of water resources infrastructure is lagging the explosive population growth, particularly in Africa and Asia. This is true especially for sanitation and waste water management, but also for both domestic water quantity and quality. Furthermore, droughts and floods disproportionately affect cities in the developing world, with impacts falling most heavily on the poor because slums are frequently located in flood-prone areas and not connected to centralized water supply and waste-water networks. Water supplies for many of these cities are also vulnerable to international boundary water resource management issues where multiple countries have jurisdiction over a watershed or an aquifer. Trans-boundary water resource management issues, exacerbated by population growth, geographic redistribution, and climate change, add a layer of complication to problems faced by cities of developing and developed nations. Further, water resource management challenges are exacerbated by extremes and changes in weather and climate, such as changes in evapotranspiration and in the frequency and intensity of precipitation. Improved understanding and predictions of these changes are key to addressing better water resource management. The Hydrological Ensemble Prediction Eperiment (HEPEX), an international project to advance technologies for hydrological forecasting, has the potential to provide needed forecasts to mitigate problems suffered by urban populations in developing countries and others. The AMS science community could support this growing population with the science enterprise it represents. Application of environmental forecasts and data such as atmospheric and hydrologic variables has considerable potential to inform sustainable water management and effective infrastructure investment in these areas This session invites presentations in the above areas, specifically forecasting and mitigating impacts of floods and droughts faced by urban poor, HEPEX products and services, and trans-boundary water management issues. Both U.S. and non-U.S. authors are encouraged to submit abstracts.