"Our understanding and ability to predict and respond to changes in the hydrologic environment cannot be properly addressed in the absence of reliable precipitation information. Proposed research aims at investigating ways to improve the quantitative precipitation estimation (QPE) associated with hydrological forecasting. Our research is facilitated by multi-instrument observations available from field campaigns in North Italy and Athens associated with complex terrain and urban environment. The scientific merit of this proposal is the synergistic use of rainfall observations from the multiple sensors available from the field experiment, which will uniquely support investigations on rainfall and precipitation classification estimation from X-band dual-polarization radar observations. The research questions to be addressed are: What is the dependence of X-band dual polarization rainfall estimation on scale and radar range? What is the relative accuracy of X-band polarimetric rain estimates to standard lower frequency (C-band) operational radar systems? How do improvements in rain estimation by X-band propagate in flood simulations and what is the dependence on scale, basin size and the complexity of the hydrological model used in the rainfall-runoff transformation? Our research questions are consistent with some of the European Research Area (ERA) priorities on QPE. X-band radar could be an economically affordable solution to the problem of filling up critical gaps in current operational radar networks. Furthermore, this project is aligned to the ERA's area of interest on “sensors and sensor networks.” X-band dual-polarization radar could be an attractive sensor for use in planed hydro-meteorologic observatories for flash flood applications."