Seasonal Climate Outlook of China in Summer 2017 Zhihai Zheng, Yongguang Wang Beijing Climate Center April 25, 2017

BCC-CSM forecasts + + Started from 01 April hgt500 N BCC model forecast for JJA 2017 shows a near normal anomaly western Pacific Subtropical High (WPSH) and a positive anomaly over Indian Ocean, and an anticyclonic anomaly occupies northern China, indicating a weakening monsoon, especially in northern China.

WPSH and Philippine Sea anticyclone WPSH intensity Philippine Sea anticyclone Near normal western Pacific subtropical high and the negative sea level pressure anomalies over the Philippine Sea

BCC-CSM Forecasts Started from 01 March Started from 01 April enhanced precipitation over southern China and suppressed precipitation in northern and northeast China.

Statistical correction to Dynamical model - FODAS Multi-model ensemble prediction (MODES) integrated three models (BCC-CSM, EC, and CFSV2) enhanced precipitation over southern China and suppressed precipitation in northern and northeast China More precipitation in most of China.

Based on statistical analyses: Based on dynamical models: The western North Pacific subtropical high would be near normal . More precipitation may occur from the South China to the middle and lower reaches of Yangtze River. Based on statistical analyses: Possible impacts from the external-forcings： The evolution of ENSO Tibet plateau snow cover

Prediction of ENSO evolution In March 2017, Sea surface temperatures (SSTs) were above normal in the tropical western Pacific and eastern Pacific. However, SSTs were near normal in the equatorial central Pacific, which showed an increasing trend as compared with last month. The Nino 3.4 index was 0.11℃ in March 2017. The ensemble mean of BCC-CSM1.1m (bar) indicated a warming trend of the Nino3.4 index in the following six months. BCC forecasts the SSTs will be near or above normal in spring and summer of 2017.

Impacts of the transition from cold phase to warm phase composite precipitation before 1980s after 1980s composite H500 - + After the 1980s,the transition from cold phase to warm phase favors more precipitation over southern China and less precipitation in northern China. The composite H500 suggest that positive anomaly occupies northern China.

Impacts of Subtropical Indian Ocean Dipole composite Precipitation BCC-CSM model predicts that the positive SIOD would persist, it favors more precipitation over southern China and less precipitation in northern China

Impacts of rapid increase of snow cover over the TP Feb. 2017 March 2017 cor. between snow cover in march and precip in June TP snow cover in March 2017 is the third most since 1973. TP snow cover in March has the significant positive correlation with precipitation in southern China in June. It favors a weak monsoon and more precipitation over southern China in early summer.

Impacts of the triple SST pattern over North Atlantic Correlation BCC-CSM model predicts that the positive triple SST pattern over North Atlantic would persist, it favors less precipitation in Hanjiang River Basin.

Summary Dynamic models predict a near normal WPSH , and more precipitation occur from the South China to the middle and lower reaches of Yangtze River. The transition from cold phase to warm phase in equatorial central-eastern Pacific favors more precipitation over southern China and less precipitation in northern China. The rapid increase of snow cover over the TP favors more precipitation over southern China in early summer.

Prediction of precipitation anomaly percentage in JJA 2017 A: above normal B: below normal N: near normal N B A The precipitation over China in JJA 2017 would be more than normal from the South China to the middle and lower reaches of Yangtze River.Less than normal precipitation might lie in Hanjiang River Basin, and southern Northeast China.

谢谢！