Assessing uncertainties in quantitative precipitation estimates from polarimetric radar in complex terrain and their impacts on simulated streamflow

Developing reliable spatially-distributed quantitative precipitation estimates (QPE) over complex terrain regions remains a fundamental challenge in hydrometeorological science and in making accurate streamflow forecasts. Polarimetric radar has demonstrated a significantly improved capability to provide quantitative precipitation information compared to single polarization, single reflectivity-based radar precipitation estimates. This study extends previous work on this topic by examining the performance of a few different quantitative precipitation estimate products from single reflectivity and multi-polarization methodologies over the complex terrain region of the Colorado Front Range. We assess retrieval methodologies and QPE products from 3 different radar platforms against a fairly dense network of surface precipitation gauge stations and for several different warm season precipitation events. Our results demonstrate that the principle advantages in the use of polarimetric-based products is that they have improved rainfall discrimination (rain/no rain and rain versus hail) capabilities which appears to better represent the actual structure of local convective precipitation events. While single reflectivity QPE products can be tuned to eliminate the mean bias in estimated precipitation, they can not be corrected for this lack of spatial discrimination capability. Applying these rainfall products to a physics-based distributed hydrological model shows that simulated streamflows that are driven by polarimetric-based QPE products tend to result in result in more realistic streamflow responses. However, hydrological models can often be calibrated to compensate for errors in forcing data which can confound the assessment of precipitation products. Hence, we also show that use of polarimetric-based products tends to result in the selection of more physically-plausible hydrological model parameters which supports the notion that polarimetric-based QPE products provide somewhat superior information quality than single reflectivity products.