2016年汛期气候预测效果评述及主要先兆信号与应用

Overview of Climate Prediction of the Summer 2016 and the Precursory Signals

2016年汛期预测较好把握了"全国气候年景状况总体差,降水偏多,涝重于旱,洪涝灾害比1983年重,但比1998年轻"的总趋势,准确预测了长江流域降水异常偏多和严重的汛情,对2016年东部地区季节内雨季进程"华南前汛期开始早,南海夏季风5月第5候爆发,长江中下游入、出梅晚且雨量明显多,及华北雨季开始晚、雨量接近常年到略偏多"的预测与实况也一致。对台风强度强,活跃程度前弱后强的预测与实况基本吻合,对夏季全国大部气温正常到偏高,尤其是我国西北大部气温异常偏高及盛夏江南华南阶段性高温热浪的预测也接近实况。但对我国北方地区降水的预测存在较大偏差,未能正确预测华北降水异常偏多和7—8月东北地区明显少雨。2016年汛期预测中重点考虑了冬季超强El Nino事件及其衰减后热带印度洋海温接力作用对夏季风环流的影响,认为夏季尤其是夏季前期西太平洋副热带高压强度异常偏强,位置明显偏西,东亚副热带夏季风强度弱,这些都直接造成长江中下游地区降水明显偏多。

In summer 2016, climatic condition in China was worse than normal. The average precipitation all over China was more than normal and floods were more severe than droughts. The disasters caused by floods in 2016 were much heavier than the flood disasters in 1983, but weaker than those in 1998. Extreme heavy rainfall occurred along the Yangtze River valley, leading to severe flood disasters. The pre-flood sea- son in South China began earlier. The South China Sea summer monsoon started in the 5th pentad of May. Both the beginning and the ending dates of the Chinese Meiyu in the Yangtze River were later than normal, but its intensity was much stronger than normal. The rainy season in North China ended also later and the rainfall during the period was slightly more than normal with a positive percentage of 20%. All these fea-tures were forecasted well in the climate prediction issued in March 2016. The forecasts captured the facts that the mean intensity of all the typhoons during the year was stronger and they became more active after July. The forecasts also provided a correct prediction that it was warmer in most regions of China in summer 2016, especially in the northwestern China. The heat waves that occurred in late July in southern China were also predicted well. However, obvious errors appeared in the precipitation forecasts for northern China, especially the extreme flood in North China in July and the droughts in Northeast China in July and August. In making the forecasts, the potential influences of the super El Nino event and the possible roles of the tropical Indian Ocean were considered in great detail. Influenced by the tropical sea surface temperature anomaly, the western Pacific subtropical high was thought to be stronger than normal and extend more westward, and the East Asian summer monsoon would be weaker than normal. These prediction results were consistent with the observations, revealing the main causes for the floods along the Yangtze River.