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ABSTRACT (Maximum 200 words)This final report dociments the results obtained through the final phase of the research study. It consists of two papers that have been submitted for publication based on the research. THe objective of this project is to quantitatively evaluate the worth of radar-rainfall estimates for physicallybased hydrologic modeling. These two papers contain valuable results. To sunnarize, our study has shown that the physical relationship between radar reflectivity and rainfall rate begins to disappear at a range of approximately 60 km from the radar site for radars with approximately 1 degree beam width. At farther ranges, radar returns are significantly affected by the horizontal and vertical gradients of cloud water. This result was verified through careful testing using a simulation methodology wherein convective rainfall is simulated using the Advanced Regional Prediction Model (ARPS), a radar simulator, and the two-dimensional hydrologic model CASC2D. Techniques to correct runoff predictions for likely errors using a Bayesian approach are suggested. The primary advantage of radar observations of precipitation compared with traditional rain gauge measurements is their high spatial and temporal resolution and large areal coverage. Unfortunately, radar data require vigorous quality control before being converted into precipitation products that can be used as input to hydrologic models. In this study, a physically-based atmospheric model of convective rainfall is coupled with an active microwave radiative transfer model to simulate radar observation of thunderstorms. Radar observations of these storms are generated and used to evaluate the propagation of radar-rainfall errors through distributed hydrologic simulations. This physically-based methodology allows one to directly examine the impact of radar-rainfall estimation errors on land-surface hydrologic predictions and to avoid the limitations imposed by the use of rain gauge data. Results indicate that the geometry of the radar beam and coordinate transformations, due to radar-watershed-storm orientation, have an effect on radar-rainfall estimation and runoff prediction errors. In addition to uncertainty in the radar reflectivity vs. rainfall intensity relationship, there are significant range-dependent and orientation-related radar-rainfall estimation errors that should be Hatim Osman Sharif-University ...