Application of an interannual increment method for summer precipitation forecast in Southwest China

Based on monthly precipitation observations collected at 80 stations in Southwest China and NCEP/NCAR reanalysis data, the method of annual increment is implemented to investigate interannual increment of atmospheric circulation in the preceding winter and spring, which influences interannual increment of summer precipitation in Southwest China. Five key factors have been selected to establish an interannual incremental prediction model for summer rainfall in Southwest China by using multiple regression method. In the modeling stage from 1971 to 2010 for interannual precipitation increment forecast, the fitting rate of the prediction model is 0.78. In the post-test seven years from 2011 to 2017, the forecast is in phase with observations in six out of the seven years, and the root mean square error of percentage precipitation anomalies is 16% in the return test from 2011 to 2017. The regression equation is established station by station to investigate the prediction effect on various types of precipitation anomaly, and the PS score in the recent five years is higher than that of operational forecasts. Therefore, the establishment of the model and its application are of great significance for the improvement of summer precipitation forecast in Southwest China.