This year, China has experienced numerous and long-lasting heavy rainfall events, with river floods occurring early and developing rapidly, creating a severe and complex flood control situation. In flood prevention and preparedness, "forecasting" comes first—flood monitoring, forecasting, and early warning are crucial.

"Digital rivers" going online, "aerial sentinels" on duty, rain-measuring radars put into use... During this year's flood season, localities have strengthened "technical defense" capabilities and accelerated the building of a "smart flood control" system, providing strong technical support for winning the modern flood control battle.

Digital twin simulates flood processes in advance

In Guiping City, Guangxi Zhuang Autonomous Region, the Datengxia Water Conservancy Hub Project lies across the Nutan site at the exit of the Datengxia Gorge. It is a controlling flood control hub project in the Pearl River Basin.

From late June to early July, affected by continuous heavy rainfall, an obvious flood process occurred in the upper and middle reaches of the Xijiang River in the Pearl River Basin. The Xijiang River experienced four numbered floods in succession, and the Datengxia Water Conservancy Hub Project faced flood control pressure and challenges.

At the Datengxia dispatch center, Li Ying, a water regulation engineer at Datengxia Company, kept her eyes fixed on the monitoring screen. Facing the menacing floods, a new technology gave her more confidence: "During this year's flood control process, the digital twin water conservancy system played an important role."

Digital twin water conservancy refers to the deep integration of information technologies such as big data, cloud computing, and artificial intelligence with water conservancy operations, real-time mapping of rivers, lakes, and water conservancy projects into the digital world, thereby simulating flood evolution trends and effectively supporting precise decision-making. The Digital Twin Datengxia is equipped with a self-developed full-chain forecast and dispatch model of "rainfall—runoff generation—confluence—evolution."

The large screen displayed information on the Datengxia project basin and hydrological stations. Li Ying carefully checked the real-time satellite cloud images as well as upstream and downstream water levels and flows. Suddenly, on the observed rainfall map, a patch of purplish red appeared in the Liujiang area, indicating that an extreme rainstorm of more than 400 millimeters had occurred in the region, which meant that a new round of water level rise was about to occur in the basin.

Based on meteorological and hydrological data, Li Ying began using the digital twin model to simulate the water level rise trend. In less than half a minute, the model calculated that the flood flow would rise to more than 30,000 cubic meters per second in the next 48 hours, indicating a severe flood control situation.

The dispatch center immediately notified relevant departments to hold consultations. During the consultation, Li Ying used the digital twin model to conduct dynamic simulations of different flood interception and peak-shaving dispatch schemes. The simulation results showed that different dispatch schemes had considerably different impacts on relevant areas and personnel.

Participants discussed the safety risks and dispatch effectiveness of different schemes, selected the best dispatch scheme, and promptly communicated with the Pearl River Water Resources Commission of the Ministry of Water Resources. Under the unified command of the Pearl River Flood Control and Drought Relief Headquarters, upstream reservoirs such as Longtan intercepted floodwater in advance, reducing the peak inflow to Datengxia; the Datengxia Water Conservancy Hub precisely controlled discharge and intercepted floods, effectively alleviating flood control pressure in the middle and lower reaches of the Xijiang River.

"Digital twin water conservancy has effectively promoted the realization of the 'four forecasts' functions of forecasting, early warning, simulation, and contingency planning. During this year's flood season, when responding to the four numbered floods on the main stream of the Xijiang River, we basically achieved a 10-day advance forecast of floods and an accurate judgment of the water level rise process 48 hours in advance," Li Ying said.

In recent years, the construction of digital twin water conservancy has continued to advance. The seven major river basins, including the Yangtze, Yellow, and Huai rivers, have accelerated the building of digital twin platforms, strongly supporting flood control dispatch management in the basins.

On June 28, the Yangtze River's No. 1 flood of 2024 formed and continued to develop and evolve. After analysis and judgment using the digital twin flood storage and detention space platform, the Yangtze River Water Resources Commission of the Ministry of Water Resources issued a "call-and-response" reminder for Guiliangzhou (a single-retreat polder) in Jiayu County in the Chenglingji reach of the Yangtze River. Local authorities promptly evacuated people from the polder, and because of early detection and early warning, flood losses were effectively reduced.

On July 18, the Weihe River's No. 1 flood of 2024 formed. The Xiaolangdi Water Conservancy Hub used the digital twin system to simulate changes in reservoir water level and inflow and outflow, as well as the timing of sediment release and the process of sediment concentration changes, and calculated and generated the optimal hub dispatch scheme, making full preparations for flood discharge and sediment flushing at the Xiaolangdi Water Conservancy Hub.

Drones open an "all-knowing" perspective

At 10 a.m. on July 3, an urgent phone rang in the office of Jiangxi Air Future Technology Innovation Group (referred to as "Air Future"). The emergency management department called, asking Air Future to send a drone flight team to Hukou County, Jiangxi Province, to conduct emergency inspections of the Yangtze River dike.

In late June and early July, the water level of the Jiujiang section of the Yangtze River in Jiangxi continued to exceed the warning line, threatening dike safety. After receiving the task, the Air Future drone flight team immediately rushed to Hukou County.

"There's no road ahead!" Li Shurui, a member of the flight team, sat in the vehicle, frowning as he looked at the flooded road in front of him. At that moment, there were still about 4 kilometers to the target polder dike. "We can't get through, but the drone can," Li Shurui said as he got out of the vehicle and, together with his colleagues, placed the drone in an open area.

The flight team controlled the drone to take off and fly toward the dike. The drone flew along a preset route and, after reaching the sky above the dike, began taking photos and videos of the dike from multiple angles.

"Through these photos and videos, we found that the water level was too high at some dikes, and we also discovered a landslide disaster," Li Shurui said. The flight team reported the findings to the emergency management department.

The images and videos captured by the drone were uploaded in real time to Air Future's back-end working team, which quickly generated a 3D model from the data. After a series of operations such as noise reduction and coordinate calibration, the final high-precision 3D model was transmitted to the emergency management department.

"The 3D model can be zoomed in and out at scale and switched between angles so that the detailed conditions of the dike can be clearly viewed," Li Shurui said. The model can also compare real-time data uploaded by the drone with historical data, thereby predicting potential risks, discovering hidden dangers, and providing technical support for flood situation assessment and response strategy formulation.

After participating in many drone flood control missions, Li Shurui said that drones have become "aerial sentinels" for monitoring flood conditions. Compared with traditional dike patrol methods, drones have significant advantages in mobility and safety.

On the front lines of flood control and emergency rescue, drones, with their efficient, flexible, and precise characteristics, are increasingly becoming an important technological force.

In late June, during large-flow flood discharge at Qingshan Reservoir in Hangzhou City, Zhejiang Province, intelligent cruise drones carried out inspections of blind zones in front of the gates, comparison of reservoir shoreline conditions, and AI automatic analysis of monitoring images, allowing reservoir managers to "control the reservoir area situation on a single screen" in the central control room. "Drones have opened an 'all-knowing' perspective for us and helped us collect first-hand data such as the inundation range of the reservoir shoreline and the operating conditions of flood discharge gates," said the person in charge of Qingshan Reservoir.

On July 18, above Suokou Reservoir in Jiuzhi Town, Hejiang County, Sichuan Province, a drone flew at a constant speed, collecting 3D oblique photography data of Suokou Reservoir. The high-definition images captured by the drone aerial survey will be used to produce VR panoramic images and 3D real-scene modeling of flood control and disaster reduction risk points.

On July 28, a breach occurred at Sixin Dike in Yisuhe Town, Xiangtan City, Hunan Province. At the emergency rescue site, workers operated surveying and mapping drones to conduct tactical mapping of the breach site and surrounding areas from above and to collect 360-degree panoramic images, providing data support for the subsequent breach closure operation.

Rain-measuring radar monitors "rain in the clouds"

Near the Lugouqiao Flood Diversion Hub on the Yongding River in Fengtai District, Beijing, stands a 45-meter-high iron tower. At the top of the tower, a water conservancy rain-measuring radar rotates at a constant speed, scanning once every 40 seconds and continuously outputting real-time rainfall data.

Before this year's flood season, the Beijing Municipal Water Authority built three rain-measuring radars in Baicaopan, Dongdatuo, and Lugouqiao within the Guanting Mountain Gorge section of the Yongding River in Beijing and applied them in a network, achieving full coverage of "rain in the clouds" monitoring in the Guanting Mountain Gorge section of the Yongding River.

Wang Lin, chief hydrological forecaster of the Ministry of Water Resources, introduced that traditional flood forecasting systems are mainly based on observations of "rain that has fallen to the ground" for flood forecasting, and the lead time is relatively limited; rain-measuring radar, however, can monitor "rain in the clouds" and extend the flood forecast lead time.

Water conservancy rain-measuring radar is also clearly different from traditional meteorological weather radar. Wang Lin introduced that rain-measuring radar observes liquid water in the near-surface atmosphere within the range from the ground to an altitude of 2 kilometers, while meteorological weather radar observes all meteorological elements in the atmosphere from the ground up to the tropopause, within an altitude range of 20–30 kilometers. Rain-measuring radar has relatively obvious advantages in time efficiency of rainfall monitoring, spatial resolution, and the accuracy and stability of networked monitoring, and can provide more comprehensive and reliable data support for flood forecasting.

On July 12, a heavy rainfall process occurred in Beijing, and the networked monitoring effect of the three rain-measuring radars began to show. Compared with observed rainfall, the 1-hour and 2-hour extrapolated rainfall forecasts from the rain-measuring radars achieved hit rates of 82% and 79%, respectively.

Since last year, various regions have accelerated the advance construction of a batch of rain-measuring radars in areas where rainstorms and floods are concentrated in important river basins, at major water conservancy projects, and in areas prone to mountain torrent disasters, so as to accurately monitor and forecast rain and water conditions.

On a high mountain in Longmen Town, Lushan County, Sichuan Province, a spherical facility attracts attention. This is the first rain-measuring radar built and put into use in Sichuan Province. Information such as the 3D structure and rainfall intensity of rain clouds is detected by the rain-measuring radar and transmitted in real time to the computer screen in the flood control duty room of the Lushan County Water Resources Bureau. In August 2023, Lushan County used water conservancy rain-measuring radar to accurately predict mountain torrents and issued early warnings to evacuate more than 100 people from dangerous areas in advance.

Since the start of this year's flood season, Hunan Province has, based on rainfall monitoring and forecast conditions from water conservancy rain-measuring radars, effectively issued SMS warnings of flood-causing and disaster-causing risks, successfully warned of water level changes in small and medium-sized rivers such as Jinjing River and Guitang River, and seized the initiative for decision-making by water conservancy departments.

Wang Lin said that next, the Ministry of Water Resources will focus on promoting the application and construction of rain-measuring radars in small and medium-sized rivers and areas prone to rainstorms and floods, fully leverage the "rain in the clouds" monitoring capability of rain-measuring radars, and further extend the flood forecast lead time and improve forecast accuracy.