Meteorology and hydrology of the Pearl River system

The Pearl River Basin is located in the subtropical zone. The Tropic of Cancer crosses the central part of the basin. The climate is mild and rainy. The average temperature for many years is between 14 and 22°C. The average rainfall for many years is 1200 to 2200mm. The rainfall distribution is obviously from the east to the east. It gradually decreases toward the west, and the rainfall is unevenly distributed within the year, with large regional distribution differences and large inter-annual changes.

The average annual river runoff of the Pearl River is 336 billion cubic meters, including 238 billion cubic meters in the West River, 39.4 billion cubic meters in the Beijiang River, 23.8 billion cubic meters in the East River, and 34.8 billion cubic meters in the Delta. Runoff is extremely unevenly distributed throughout the year. The flood season from April to September accounts for about 80% of the total annual runoff, and the three months of June, July and August account for more than 50% of the annual runoff. The Pearl River is rich in water resources. The per capita water resource in the entire basin is 4,700 cubic meters, which is equivalent to 1.7 times the national average. However, large inter-annual changes and uneven spatial and temporal distribution have resulted in frequent natural disasters such as floods, waterlogging, droughts, and saltwater in the basin.

The characteristics of floods in the Pearl River Basin are high peak, large volume and long duration. The main weather systems causing floods in the basin are mainly peaks or stationary peaks and southwest troughs, followed by tropical depressions and typhoons. Annual heavy rains and floods mostly occur in June, July and August.

The dry season in the Pearl River Basin is generally from October to March of the following year. The multi-year average low water runoff is 80.3 billion cubic meters, accounting for only about 24% of the annual runoff in the entire basin. The minimum flow rate in the dry season at Xijiang Wuzhou Station is 720 cubic meters/second, Beijiang Jiaoshi is 130 cubic meters/second, and Dongjiang Boluo Station is 31.4 cubic meters/second.

The Pearl River is a river with little sediment, with a multi-year average sand content of 0.249 kg/cubic meter and an annual average sand content of 88.72 million tons. According to statistical analysis, about 20% of the sediment is deposited in the Pearl River Delta river area every year, and the remaining 80% of the sediment is exported to the South China Sea through Badakou Gate.

The tides at the Pearl River Estuary are irregular semi-diurnal tides. The Pearl River Estuary is a weak tidal estuary with a small tidal range, with an average tidal range of 0.86 to 1.6 meters and a maximum tidal range of 2.29 to 3.36 meters. The multi-year average of high tide volume at Badakoumen is 376.2 billion cubic meters, and the multi-year average of low tide volume is 702.2 billion cubic meters, with a net loss of 326 billion cubic meters.