This volume is a collection of a selected number of articles based on presentations at the 2005 L'Aquila (Italy) Summer School on the topic of "Hydrologic Modeling and Water Cycle: Coupling of the Atmosphere and Hydrological Models". The p- mary focus of this volume is on hydrologic modeling and their data requirements, especially precipitation. As the eld of hydrologic modeling is experiencing rapid development and transition to application of distributed models, many challenges including overcoming the requirements of compatible observations of inputs and outputs must be addressed. A number...