Sensitivity analysis of convective RegCM4 schemes in simulation of precipitation for west Iran by using CSIRO-MK36 dataset

The present study was carried out in west of Iran including: Hamadan, Kurdistan and Kermanshah provinces in an area of 72336 square kilometers. The selected region is located 45 degrees, 20 minutes to 49 degrees and 36 minutes longitude, and 33 degrees, 37 minutes to 36 degrees and 30 minutes latitude. Regarding the studied period and the overlapping of recorded rainfall data in the meteorological stations, 13 synoptic stations including Hamedan, Toyserkan, Nahavand, Malayer, Kermanshah, Islamabad, Sarpol-e-Zahab, Kangavar, Sanandaj, Baneh, Bijar, Marivan and Saqez in three provinces was used. RegCM4 model has been run for 10 years by definite and constant boundary conditions for all four schemes including Grell, Kuo and Emanuel. Grell scheme itself has been divided into two different schemes of Arakawa-Schubert (AS) and Fritch-Chapel (FC). In order to investigate errors of model outcomes, simulated and observed rainfall For the 13 selected stations in Hamedan, Kermanshah and Kurdistan provinces were extracted using coding in the NCL environment. Results: In all three provinces, Emanuel Scheme has the lowest value for RMSE, and Grell A.S. Schema has the highest amount of RMSE in the provinces of Kermanshah (49.84 mm) and Kurdistan (55.35 mm), and for the Hamadan province, the Kue Scheme has the highest value (36.13 mm). In the case of Bias Error, in Hamedan and Kurdistan provinces the least amount of error is devoted to the Emanuel Scheme (about 18 mm in both provinces), but in Kermanshah province, KUE scheme has the lowest value of the Bias Error ( 24.96 mm). In winter, except the KUE scheme, the three other schemes simulated the rainfall values more than real values, and Emmanuel scheme had the highest over-estimated (about 63 mm). Also in this Season, Grell F.C. With an average of 13 mm, the difference from the actual values, showed the lowest error. In spring, Kue Scheme also simulated rainfall values for all stations less than actual values, but the other three schemes simulated the rainfall values more than real values, and the Emanuel Scheme with an average of 62 mm error was the best For the whole study area. In summer, all schemes simulated rainfall values more than real values, and KUE (1.2mm bias error) and Grell A.S. (122 mm bias error) showed the best and worst results for the whole region, respectively. In the fall, only the Kue scheme simulated the rainfall values less than actual values, and the best simulation was for the Malayer station with a 99.2 mm error. The other three schemes, like the other Season, simulated rainfall values more than real values, and Grell F.C. With an average 6 mm error in the region and Kue with an average of 143 mm bias error in the region, respectively, showed the best and worst results.
Conclusion: on an annual scale for all three provinces, Emanuel Scheme showed the least RMSE values (18.96, 28.95 and 20.69 mm for Hamedan, Kermanshah, and Kurdistan provinces respectively). In addition, Grell A.S. Scheme has highest RMSE and MBE errors for Kermanshah (49.84 mm) and Kurdistan (55.35 mm). On seasonal scale, Emanuel scheme shows the lowest RMSE for the autumn (68.76 mm) and winter (66.8 mm).