FGOALS-f2气候预测系统对西南地区持续性极端降水的次季节预测评估

Sub-seasonal Prediction of the Regional Persistent Extreme Precipitation in Southwest China by GOALS-f2 Climate Prediction System

区域持续性极端降水具有降水范围广、时间久、强度大且灾害性强的特征,亟需提高其预测时效和准确性。本文通过挑选1999—2019年西南地区发生的7个区域持续性极端降水事件,评估了FGOALS-f2 S2S模式对西南地区持续性极端降水的次季节预测性能。结果表明:FGOALS-f2对四川盆地及周边地区降水存在明显低估,导致了模式所预测的极端降水阈值在四川盆地、重庆和贵州大部分地区比观测偏低约15 mm/d,而在四川西部及云南等高海拔地区基本与观测接近。降水强度的模拟误差进一步导致在该区域发生的持续性极端降水和短时极端降水事件强度被模式低估,但偏差基本不随预测时效延长而变化。在极端降水发生概率方面,模式对区域持续性极端降水事件和短时极端降水事件的命中率、误警率和Heidke技巧评分在1~10 d内迅速下降,然后在11~30 d内基本维持不变,但区域持续性极端降水的预测性能明显优于短时极端降水。可见,该模式对区域持续性极端降水发生概率的预报技巧更好,可为西南地区极端降水的次季节预报提供科学参考。

Regional Persistent Extreme Precipitation Events(RPEPEs),characterized by wide-range,long-time and high-intensity precipitation,usually lead to severe disasters.Based on 7 RPEPEs occurred in Southwest China from 1999 to 2019,the sub-seasonal prediction performance of the FGOALS-f2 S2S model for RPEPEs in Southwest China was evaluated.The main results are as follows:FGOALSf2 underestimated the summer precipitation in the Sichuan Basin and its surrounding areas,which resulted in the predicted extreme precipitation thresholds being about 15 mm/d lower than the observations in the Sichuan Basin,Chongqing,and most of Guizhou,while the thresholds were close to observations in the high-altitude areas of western Sichuan and Yunnan.The simulation error of precipitation intensity further led to the underestimation of the intensity of RPEPEs and short-term extreme precipitation events in those regions,but the errors did not change with the prediction leading time.Regarding the occurrence probability of extreme precipitation,the probability of detection,false alarm ratio and Heidke skill score of the RPEPEs and short-term extreme precipitation events decreased rapidly within the leading 1~10 days and then remained nearly constant during the leading 11~30 days.However,the prediction performance of RPEPEs was significantly better than that of short-term extreme precipitation.It can be seen that the prediction skill of the occurrence probability of the RPEPEs is of higher scores,which can provide scientific reference for the sub-seasonal prediction of extreme precipitation in Southwest China.