Abstract:

The northern slope of the Kunlun Mountains has a complex terrain and unique diurnal variation of precipitation, which lead to low accuracy in refined precipitation forecasting. The ECMWF model has world-leading forecast performance, but its ability to predict the diurnal variation in precipitation in complex terrain is still unclear. This study used precipitation data from automatic meteorological stations during the summer of the 2020-2023 season to verify and evaluate the ECMWF model’s forecast performance for the diurnal variation of summer precipitation at various regions on the northern slope of the Kunlun Mountains. The results show the following. (1) The 24 h cumulative precipitation forecast performance of the ECMWF model initialized at 20:00 was better than that which initialized at 08:00; the model’s precipitation forecast capability for areas above 2000 m in altitude on the northern slope of the Kunlun Mountains was better than that for areas below 2000 m in altitude; the ECMWF model’s ability to capture precipitation in the Western Kunlun Mountains was superior to that in the Central Kunlun Mountains. (2) The ECMWF model’s forecasts of daily precipitation variations exhibited the greatest discrepancies from observed precipitation between 17:00 and 02:00 the following day. The model’s predicted frequency of precipitation events was much higher than the observed frequencies, but the predicted intensity of precipitation was markedly lower the observed. During periods of low observed precipitation, the model was prone to overestimating precipitation. In regions of the western (central) Kunlun Mountains, on the north-facing slopes with elevations above 2000 m (and up to 2000 m), the model’s daily variation in precipitation significantly diverged from that of the observed precipitation. (3) The ECMWF model’s precipitation forecasts were dominated by convective precipitation (CP) in the Western Kunlun Mountains and by large-scale precipitation (LSP) in the Central Kunlun Mountains. Within the ECMWF model, LSP had a better capturing ability for observed precipitation than CP, and the discrepancies between model precipitation forecasts and observed precipitation were more likely to come from CP. These findings provide a reference for improving the accuracy of summer precipitation forecasts on the northern slope of the Kunlun Mountains and for the correction of the ECMWF model’s precipitation forecasts.

Key words: ECMWF model, diurnal variation, summer precipitation, performance assessment, northern slope of the Kunlun Mountains