Most of China’s dams were built between the 1950s and the 1980s, and many have approached or even exceeded their designed lifespan. About 36% of the dams, or some 30,000 dams, are at high risk due to structural obsolescence or lack of proper maintenance. The ageing dams that do not satisfy current flood or other loading criteria and do not adhere to current state-of-the-art practices pose significant risks to downstream regions. Hence, dam renovation or decommissioning has become a growing concern.

Dams/reservoirs pose many environmental and ecological challenges by reducing sediment flux and changing the temporal pattern of river discharge to downstream and ultimately the ocean. In water-rich river basins, the impacts on sediments are more obvious than on discharges. About 45,197 dams have been built so far throughout the Yangtze River basin. While having little impact on annual river discharge, they have caused downstream channel erosion, coarsening of bottom sediment, and erosion of the subaqueous delta. The sediment discharge of the Yangtze River, as measured at Datong Station located around 600 km from the river mouth, decreased by 94% from 490 million ton/yr in the 1950s and 1960s to 29 million ton/yr in 2008, mainly as a result of the trapping effect of the human-made dams, particularly the Three Gorges Dam. The water discharge measured at the Datong Station has remained more or less constant since the 1950s, averaging about 900 km³/yr even after the construction of the Three Gorges Hydropower Plant. The inlet has experienced declining sediment loads, and a consequent decrease in coastal salt marsh accretion and net erosion in the subaqueous delta front. The sediment loads are likely to further decline, and the middle to lower river channel and delta will continue to erode as new dams are built and the South North Water Transfer Project starts the operation. The lower sediment flux to the sea resulted in significant degradation of the Yangtze delta and posed serious challenges to maintaining the geometry of the delta and protecting Shanghai and nearby wetlands. Similarly, the 387 large and medium-sized dams/reservoirs along the Pearl River did not affect the river discharge, but led to a 33% decrease in sediment flux to the ocean.

Irrigation is often cited as a main cause for unsustainable water use in many regions, e.g. sharp declines in groundwater levels. For example, nearly 40% of water used in the main wheat production areas such as Hebei, Shannxi, Henan, and Shandong provinces is from groundwater. Among these provinces, Hebei has the highest share of groundwater in total irrigation water, as high as 68 per cent. Abstraction of non-renewable groundwater for agriculture in China has reached 20 km³ yr⁻¹ since 2000. The over-withdrawal of groundwater led to sharp declines in groundwater tables, large cones of depression, land subsidence, and intrusion of sea water. The groundwater level declined rapidly from about 10 m below the surface in the 1970s to 32 m in 2001 in Luancheng County in the North China Plain.

Irrigation has been a key cause for river discharge decline in arid or semiarid areas. Supported by the construction and operation of dams/reservoirs, agricultural water abstraction from the Yellow River increased from 155.4 m³/yr in the 1950s to 294 m³/yr in the 1990s while irrigated area increased by a factor of 10 to about 10 million ha in the 2000s. In the Haihe River basin, the total annual agricultural water use in the 1990s reached 28.5 billion m³, 32 per cent higher than the total river discharge, which led to a drop in the groundwater table.

Despite the fast expansion of water-saving irrigation, wasteful water use still remains a big problem in agriculture. According to the Ministry of Water Resources, only about 45 per cent of the water withdrawal can reach irrigated fields. This low water-use efficiency of 0.45 is much lower than the level of 0.7–0.8 in developed countries. A dilemma lies between increasing investment in water conservancy projects and insufficient capital to maintain and rehabilitate existing irrigation infrastructure. Bulk of the capital channeled through the government has gone enthusiastically to new, giant water conservancy projects while channel leakage associated with old systems has often been ignored.

Irrigation is facing intense competition from the growing demand from municipal, industrial, and environmental uses, which will pose significant challenges for China to achieve its goals of increasing grain production by 50 million tons by 2020. The steadily increasing water demand of other sectors, especially the industrial sector, has posed significant pressure to divert water away from agricultural production. The higher economic value of water use in industry leads local governments to put industrial use first when facing water-use conflicts between industry and agriculture. With decreasing water supply for irrigation, agriculture needs to increase water productivity and produce more crops for each drop of water. This has posed additional challenges to the existing irrigation schemes, which were designed primarily to maximise crop yield. The decrease in irrigation water supply renders a need for the development of irrigation scheme to be redirected to optimise irrigation volume to achieve the maximised crop water productivity