USDA: China - Flood warning

Originally published

Heavy Rain Returns to the Yangtze River Basin

In May and June, torrential rain and localized flooding killed about 800 people and damaged crops and infrastructure in parts of western, central and southern China. Drier and warmer weather in July eased the threat of further flooding and allowed the affected areas to recover. However, the return of very heavy rain in late-July has revived the possibility of flooding in the Yangtze River Basin that could be as serious as the catastrophic floods of 1998.

Precipitation in the Yangtze River Basin - 2002 vs. 1998

Rainy Season Starts Early

China's 2002 summer rainy season started about a month early and came on strong. Very heavy rainfall covered a broad section of central and southern China from April through June and caused locally-serious flooding in many areas. Hundreds of deaths and millions of dollars in economic losses were attributed to the flooding. The impact on wheat production was minor since very little is produced in the affected region, but rapeseed yield was lower than expected. The wet weather also hindered cotton planting in central China, particularly in Hubei province, where up to 30 percent of the crop reportedly had to be replanted. Some of the early rice crop in low-lying areas was washed out, and persistent heavy rain caused planting delays and germination problems for single rice, cotton, and other summer crops in the affected area.

Fortunately, several weeks of hot and mostly dry weather in July allowed water-logged areas to start drying out and rivers to recede, easing the threat of flooding in the region. AVHRR low-resolution satellite imagery indicates that lakes and rivers in the Yangtze Basin were at full capacity in mid-July but were not spilling out beyond the floodplain. [Image 1 and Close-up]. Dongting Lake (Hunan province) and Poyang Lake (Jiangxi province) stayed within their limits, and there were no apparent breaks in the dike system. In contrast, during China's last great flood of 1998, officials were forced to deliberately divert floodwater in the midsection of the Yangtze Basin to protect cities and industries downstream [Image 2] The danger was especially great for the city of Wuhan in eastern Hubei, which is divided by the Yangtze River and thus very vulnerable to flooding. One of the reasons why flooding was more serious in 1998 was the difference in the timing and distribution of the rainfall. In 1998, the heaviest rain occurred in July and August and covered a wide area of eastern China, while the rainfall in 2002 accumulated more slowly and covered a smaller geographic area.

Heavy Rain Returns in Late July

During the week of July 21 to 27, a slow-moving storm front dumped very heavy rain across central China, particularly in Hunan and Hubei provinces. The largest amounts were reported near Yueyang, which received nearly 400 mm during the period. Wuhan and Yichang also received significant rainfall in the latest storm. In the case of Yueyang and Yichang, total rainfall for the season now exceeds the totals of 1998, and the pattern of rainfall is nearly identical [Graphs]. The latest satellite imagery [Image 3] clearly shows very wet soils and standing water in Hunan, major rivers and tributaries at flood stage, and runoff flowing into already-brimming Dongting and Poyang lakes. However, the flooding is still not as serious as it was in 1998, particularly in the Dongting Lake region [Image 4]. Heavy rain also covered Anhui and Jiangsu provinces last week and raised water levels in the Huai River system to dangerous levels. Drier weather returned to the region this week and the forecast calls for near to below-normal rainfall for the next 6 to 10 days. This break in the weather will give the region a chance to recover from last week's heavy rain, but the flood danger will remain very high, especially if this summer's wet pattern continues in August.

Flooding usually causes minor crop losses in China, since the amount of cropland directly damaged by water is typically much smaller than the cropland which benefits from the additional rainfall. China posted record rice yields in 1998/99 despite the flooding that occurred, and it's possible that 2002/03 rice yields may have not been affected. However, below-normal yields are expected from the region's cotton crop which was hit by cool and wet weather last spring and excessive rainfall this summer.