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. Data assimilation is an effective tool in improving high-resolution rainfallof the numerical weather prediction (NWP) systems which always fails inproviding satisfactory rainfall products for hydrological use. The aim ofthis study is to explore the potential effects of assimilating differentsources of observations, i.e., the Doppler weather radar and the GlobalTelecommunication System (GTS) data, in improving the mesoscale NWP rainfallproducts. A 24 h summer storm occurring over the Beijing–Tianjin–Hebeiregion of northern China on 21 July 2012 is selected as a case study. TheWeather Research and Forecasting (WRF) Model is used to obtain 3 km rainfallforecasts, and the observations are assimilated using the three-dimensionalvariational (3DVar) data assimilation method. Eleven data assimilation modesare designed for assimilating different combinations of observations in thetwo nested domains of the WRF model. Both the rainfall accumulative amountand its distribution in space and time are examined for the forecastingresults with and without data assimilation. The results show that dataassimilation can effectively help improve the WRF rainfall forecasts, whichis of great importance for hydrologic applications through therainfall–runoff transformation process. Both the radar reflectivity and theGTS data are good choices for assimilation in improving the rainfallproducts, whereas special attention should be paid to assimilating radialvelocity where unsatisfactory results are always found. The assimilation ofthe GTS data in the coarser domain has positive effects on the radar dataassimilation in the finer domain, which can make the rainfall forecasts moreaccurate than assimilating the radar data alone. It is also found that theassimilation of more observations cannot guarantee further improvement of therainfall products, whereas the effective information contained in theassimilated data is of more importance than the data quantity. Potentialimprovements of data assimilation in improving the NWP rainfall products arediscussed and suggestions are further made.

hydrology and earth system sciences

Evaluation of Doppler radar and GTS data assimilation for NWP rainfall prediction of an extreme summer storm in northern China: from the hydrological perspective