Skillful Seasonal Forecasts of Summer Surface Air Temperature in Western China by Global Seasonal Forecast System Version 5

Variations of surface air temperature(SAT) are key in affecting the hydrological cycle,ecosystems and agriculture in western China in summer.This study assesses the seasonal forecast skill and reliability of SAT in western China,using the Glo Sea5 operational forecast system from the UK Met Office.Useful predictions are demonstrated,with considerable skill over most regions of western China.The temporal correlation coefficients of SAT between model predictions and observations are larger than 0.6,in both northwestern China and the Tibetan Plateau.There are two important sources of skill for these predictions in western China:interannual variation of SST in the western Pacific and the SST trend in the tropical Pacific.The tropical SST change in the recent two decades,with a warming in the western Pacific and cooling in the eastern Pacific,which is reproduced well by the forecast system,provides a large contribution to the skill of SAT in northwestern China.Additionally,the interannual variation of SST in the western Pacific gives rise to the reliable prediction of SAT around the Tibetan Plateau.It modulates convection around the Maritime Continent and further modulates the variation of SAT on the Tibetan Plateau via the surrounding circulation.This process is evident irrespective of detrending both in observations and the model predictions,and acts as a source of skill in predictions for the Tibetan Plateau.The predictability and reliability demonstrated in this study is potentially useful for climate services providing early warning of extreme climate events and could imply useful economic benefits.