Qun and Yang (1997) developed a method of seasonal prediction of summer monsoon rainfall in central-east China. The predictors are selected from a series of high correlation regions of the following fields for January-March preceding the summer monsoon:

1. Monthly 500 mb height fields of the Northern Hemisphere for 576 grid points (10-85^oN), 1951-1996.

2. Monthly sea surface temperature (SST) of the North Pacific for 286 grid points, 1951-1996.

3. Monthly temperature for 160 stations evenly distributed throughout China, 1951-1996.

4. Monthly precipitation for 160 stations evenly distributed throughout China, 1951-1996.

The above data were obtained from the Central Meteorological Observatory of China (Beijing)

The selected predictors were then combined to form multivariate linear regression equations. We have found that a 20-year time series is needed for training the regression equations in order to minimize the effect of interdecadal variability and climate change. The process for selecting the predictors and predictands as well as some details regarding the regression equations was described in the June 1997 issue of this Bulletin. Seasonal predictions for summer 1998 are made by using the regression equations trained on data from 1977-1996. The predictors are calculated from the four fields described above during the January-March season preceding the summer of 1998.

 The following 12 predictands were calculated by using the established regression equations and the forecast was made on April 21, 1998. The first 10 predictands listed below were shown in the forecast issued in 1997 (see the June 1997 issue of this Bulletin). Two additional predictands (Jrs67r, CL67r) using the same training period are also presented here. The prediction is in bold face.

1. Yanr68: Summer average rainfall anomaly in 10 stations in the mid-lower Yangtze basin (29.2-32.2 ^oN, east of 113 ^oE). +165.2 (flooding)

2. Meiyu: Percentage of total rainfall in 5 stations located in the mid-lower Yangtze basin during the period of Meiyu. 121%.

3. Onsemei: Date of onset of the Meiyu. Early.

4. Outmei: The first day after the end of Meiyu. Late.

5. Snmei: Percentage of total rainfall in 5 stations located in the southern part of Jiangsu province during the period of Meiyu. 167%

6. Jnmei: Percentage of total rainfall in 5 stations located in the middle part of Jiangsu province during the period of Meiyu. 146%

7. Huai67r: The average rainfall in 8 stations evenly distributed in Huaihe basin during June-July. 368 (flooding).

8. Huai78r: The average rainfall in 8 stations evenly distributed in Huaihe basin during July-August. Normal.

9. Jian78r: Averaged rainfall anomaly in 10 stations located in the south-eastern part of the Yangtze-Huaihe basin (30-33.6^oN, east of 114^oE) during July-August. -11.3 (normal).

10. Nor78r: Averaged summer (July-August) rainfall in 10 stations evenly distributed in North China (36-41^oN, east of 110^oE). -7.1% (below normal).

11. Jrs67r: Averaged rainfall anomaly in 7 stations evenly distributed in Jiannan region, south of the mid- lower Yangtze (27-29^oN, east of 112^oE). -127.1 (near drought).

12. CL67r: The central latitude of positive anomaly of monsoon rainfall in eastern China east of 112^oE) during June-July. 32.5^oN (in the middle of Yangtze-Huaihe basins).

The forecast calls for both an early onset and a later ending of the Meiyu of 1998. The central latitude of the monsoon rainy belt in eastern China is forecasted to be in the middle of the Yangtze-Huaihe basins during June-July 1998. Less rainfall is predicted in Jiannan region south of the mid-lower Yangtze. Given that present water levels of Yangtse and Huaihe River have been abnormally high due to an anomalously long rainy period since November 1997, and that the above forecast is for above normal rainfall, there is reason to expect that there will be considerable flooding in the Yangtze-Huaihe basin during June-July 1998. Positive anomalies of Meiyu rainfall are forecasted in the middle and southern parts of Jiangsu province with the threat of possible summer flooding from the upper reaches of Yangtze and Huaihe River. The positive rainfall anomalies in the Yangtze-Huaihe basin are forecasted to end by August 1998. The monsoon rain in North China will be slightly less than normal. In short, the forecast calls for considerable flooding in the Yangtze-Huaihe basin during June-July 1998.

References:

Qun, X., and Y. Qiuming, 1997: Seasonal prediction of summer monsoon rainfall in central-east China. Experimental Long-Lead Forecast Bulletin, 6(2), 74-79.