Evaluation of radar precipitation estimates near gap regions: a case study in the Colorado River basin

Radar precipitation estimation is very useful for hydrological and climatological studies. However, radar precipitation has inherent difficulty in estimating precipitation in mountainous regions. In developed countries such as the United States where there are extensive precipitation radar networks, gaps in the radar precipitation field are usually due to radar beam blockage by mountains. The goal of this study is to evaluate the performance of a daily radar precipitation field (Stage-II) against rain gauge measurements near radar gap areas in the Colorado River basin of the United States (southwestern Colorado, southeastern Utah, northeastern Arizona and northwestern New Mexico). We evaluated daily precipitation data for the years spanning from 2007 to 2009. Statistical score skills including correlation and bias are used for evaluation. Compared to gauge measurements, Stage-II fails to capture the altitude dependence of precipitation in the region. Bias analysis shows that Stage-II underestimates precipitation at higher elevation. Seasonal evaluations of Stage-II indicate that it underestimates cold season precipitation in the study area. Overall, the results show that the error in Stage-II precipitation estimates made within 100km from the gap area, as measured against rain gauge measurements, is considerable, and caution is warranted for its use in hydrological and water management applications.