Simulation of extreme precipitation events with cold anomaly in Tehran area

:The main purpose of this research is to improve the simulation of moderate and heavy precipitation events associated with cold anomaly in Tehran. To detect extreme precipitation events along with cold anomaly in Tehran in a sufficiently long period, the results of Khansalari et al. in the study carried out in 2017 are used. In the latter study, using statistical methods, 133 days with extreme precipitation along with cold anomaly in October to May in the 1951–2013 period were identified based on which six clusters of synoptic patterns were obtained by application of the T-mode principle component analysis to the whole dataset of 133 days. In the present study, from each cluster, one day with maximum similarity with the average pattern of the cluster was selected for numerical simulation by WRF model using the ERA-Interim data. To reach the optimal prediction of extreme precipitation events in Tehran by WRF, nine configurations consisting of four convection, two boundary-layer, three microphysics, and two short waves radiation schemes, as well as one surface-layer scheme were used. For verification, in addition to visual comparison, the forecasted data of model regular network were interpolated to irregular observation stations. Then using various verification indices, the performance of different configurations in predicting rainfall was assessed quantitatively with different thresholds. Results showed that across all the ranges of rainfall, the Tiedtke convection scheme and Mellor-Yamada-Janjic boundary-layer scheme lead to greater accuracy and better prediction of precipitation. It should also be noted that for light precipitation events, in addition to the Tiedtke convection scheme, the Kain-Fritsch scheme is also suitable