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Refections on the catastrophic 2020 Yangtze River basin flooding in southern China
Category: Commentary
Author: Chaojun Ouyang, PhD


Concept map of hydrological regulation change

During the summer of 2020, southern China suffered from catastrophic flooding, the massive basin flood mainly occurred in the Yangtze River's middle and lower reaches. As of July 20, 2020, the cumulative precipitation since the rain season started exceeded 500 mm over most of the Yangtze River Basin, reaching >1,200 mm in some areas of the lower reaches, exceeding the same period in 1998, the severest flood year in the past 60 years. Several water gauge stations at Poyang Lake and Chaohu Lake exceeded their historical record values. The water levels in the Wuhan section of the Yangtze River were among the highest ever recorded. As of July 22, 2020, 45.5 million people had been affected by the floods, with 142 people having died or were missing, and the direct economic losses expected to be around 116 billion RMB (~16.5 billion US dollars). However, the losses from this flood are much lower than those of previous major floods. For example, the catastrophic 1998 flooding led to 1,526 deaths and economic losses of 255 billion RMB (~36.4 billion US dollars). The reasons behind this are worthy of further study and discussion, and may be used for reference in the future and for other countries.

After the historic floods in 1998, China accelerated the construction of large-scale water conservancy projects on the Yangtze River's mainstream and its tributaries, including the Three Gorges, Xiangjiaba, Xiluodu, Wudongde, and Ertan dams, in addition to another ~100 large reservoirs. This increased the total flood control storage capacity to ~80 billion m3. Meanwhile, flood control levees along the Yangtze Rivers and affiliated lakes were updated and strengthened, with the levees on both sides of the Yangtze River mainstream now 2 m higher than the highest recorded water levels. Such an infrastructure has dramatically improved the flood control capacity of this region, and played a crucial role in responding to the catastrophic 2020 flooding in southern China.

In addition to the conventional human-engineered solutions (gray infrastructure), which depend on large-scale projects of canals, dams, levees, and other flood control facilities, concerted actions with eco-friendly solutions (or green infrastructure) to increase water resilience, have been undertaken over the past two decades. For example, in Dongting Lake, the implementation of the Converting Farmland to Lake policy has increased the areas of lakes by around 800 km2. Since 2015, it has become a national policy to create ¡°sponge cities,¡± which involves improving the water storage capacity of lakes, parks, wetlands, and beaches. This has changed the nation's strategy dealing with rainwater harvesting and utilization, and potentially provides hydrological regulation services for precipitation interception, filtration, and absorption, while helping to reduce the flood peaks.

It is worth noting that great technological progress over the past decade has been made with regard to making accurate weather forecasts within 5¨C7 days, as well as improvements in hydrological modeling, resulting in more accurate flood predictions. Real-time flood peak forecasting for planning operational responses has been used regularly for large basins. Such progress allows pre-disaster preventive measures to be proposed before floods occur, and to make the optimal use of large-scale water conservancy projects on the river's main and tributary streams to reduce flood peaks and to allow the safe passage of floodwaters.

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