Water issues and prospects for hydrological science in China

Zhong-bo YU*, Tao YANG Frank W. SCHWARTZ

1. State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, P. R. China

2. Department of Geoscience, University of Nevada, Las Vegas, NV 89154-4010, USA

3. School of Earth Sciences, Ohio State University, Columbus, Ohio 43210-1398, USA

Water issues and prospects for hydrological science in China

Zhong-bo YU*1,2, Tao YANG1, Frank W. SCHWARTZ3

1. State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, P. R. China

2. Department of Geoscience, University of Nevada, Las Vegas, NV 89154-4010, USA

3. School of Earth Sciences, Ohio State University, Columbus, Ohio 43210-1398, USA

As a country with one of the world’s most rapidly developing economies, China is home to wonderful opportunities for its people and the nation as a whole. An essential element for continued economic prosperity is a water supply of guaranteed quality and quantity, providing critical insurance for food safety, health, and political stability. However, China’s economic success has come with serious water resources problems, intensified by human activities and climate change. The nation is now facing extreme levels of water pollution, soil erosion, and sedimentation, along with floods, droughts, and urban storms. Taken together, these impacts have provided a serious headwind to socioeconomic development in China. This article discusses the problems and emerging opportunities for the coming generation of water scientists and engineers.

At first glance, China seems to possess abundant water, ranking the sixth in the world in terms of its overall water resources (2.8 × 103km3). However, because of its large population, the per capita availability of renewable freshwater, at 2.3×103m3/year, is only 25% of the world’s average. Moreover, water shortages are aggravated by the uneven temporal and spatial distributions of water resources. The inter-annual distribution of water resources is determined mainly by the annual continental monsoon. Across much of China, 60% to 70% of annual precipitation occurs during the summer. In more northern areas, summer rainfall makes up as much as 80% of the annual amount. There is also marked variability in the geographic distribution of precipitation. The largest amount of annual precipitation, exceeding 1 600 mm/year, occurs in the coastal areas of the southeast. Rainfall amounts decline markedly as one moves north and west. For example, northwestern areas of China receive less than 50 mm/year of precipitation. A significant challenge in water management is the mismatch between the distribution of water and the distributions of people and the arable land.

China’s water problems often swing between extremes. In drought years, water is in short supply, creating enormous problems (especially in crop production). In wet years, large

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*Corresponding author (e-mail: zyu@hhu.edu.cn)amounts of rainfall often occur over short time periods, bringing about flooding and losses in lives and property. Still, problems in natural water availability are only part of the story.

Water pollution and degradation of aquatic ecosystems have produced massive damage to the function and integrity of water systems. In China, an emphasis on economic growth and self-sufficiency, magnified by the country’s huge population, has created problems of a scope and severity beyond what the world has previously experienced. Not surprisingly, the solutions to the most immediate short-term challenges of providing water and food to China’s people and reducing flood losses are large-scale and expensive, essentially requiring the re-plumbing of river systems to distribute water and control flows, in order to better balance needs and opportunities. Such a strategy has required not only a massive investment of public funds in water management infrastructure around the country, but also a reluctant acceptance of the accompanying environmental problems.

China’s water resources challenges also coincide with a period of change that will add complexity. The population distribution in China is not static, with increasing migration of people from the countryside to cities, impacts related to urbanization, and renewed needs for water resources. It is also not clear yet how anthropogenic climate change will affect water resources in China. Here, we have identified the grand challenges influencing hydrological sciences and sustainable water management in China. We will now look at these in more detail.

1 Floods and droughts

Floods and droughts have been among the most visible contributors to death and destruction. According to historical records, China has experienced 1 056 large-scale droughts and 1 092 severe floods over the 2 155 years from 206 B.C. to 1949 A.D. Thus, major droughts and floods reoccur every two years on average. Local-scale impacts are observed even more frequently. Such natural events have led to the deaths of millions of people and, even now, the threats associated with floods and droughts cannot be underestimated.

Variability of the monsoon climate, topography, land cover, sedimentation, and human activities are the main factors controlling the occurrence and severity of floods. Rainstorms brought by summer monsoons and tropical cyclones or typhoons commonly produce lowland flooding. Presently, one-third of agricultural land and two-thirds of cities are under the threat of flooding, which could have severe and devastating effects since many of the flood protection works are only designed for events with recurrence intervals of 10 to 20 years. With the largest floods, even the flood-control infrastructure itself may contribute to the severity of damage.

Droughts and the accompanying water shortages represent another major problem related to hydrological extremes. Droughts have significant implications for agriculture and food production, which represent a vital component of the nation’s economy, affecting about 70% of the population in rural areas. Water shortages are a particularly serious problem for urbanregions, with nearly 67% of the 660 cities in China already short of water and 108 of them under severe water stress.

2 Water pollution and degradation of aquatic ecosystems

Water pollution is a common worldwide problem contributing to the diminution of water resources. China is no exception. The careless disposal of hazardous municipal solid waste, discharges of untreated industrial and municipal wastewater, and agricultural runoff of fertilizers, pesticides, and manure have resulted in severe and widespread contamination of surface water and groundwater. A recent national water quality survey showed that only 58.3% of river reaches, 49.7% of lakes, 79.5% of reservoirs, and 38.7% of groundwater produced from wells met quality criteria for source water supplies. The most severely polluted watersheds include the Huaihe River, the Yellow River, the Haihe River, and the Song-Liao River basins, and the region around Taihu Lake, located in the lower part of the Yangtze River Basin. In rivers and streams, the most significant problem is excessive chemical oxygen demand related to the disposal of reactive organic compounds. Oxygen concentrations in surface waters fall too low to support fish and other aquatic life. Another serious problem is water pollution from toxic and accumulative organic compounds, as well as heavy metals.

The problem of water quality in lakes and reservoirs is primarily associated with elevated concentrations of nitrogen and phosphorus, leading to eutrophication. From a regional perspective, persistent organic pollution is particularly serious in urban lakes of the south and lakes across the northeastern plains. Salinization tends to be a relatively more common problem in lakes of the arid northwest. In recent years, tremendous efforts have been focused on restoring the water quality of three of the most seriously polluted lakes: Taihu Lake, located in the Yangtze River Delta, Chaohu Lake in Anhui Province, and Dianchi Lake in Yunan Province.

3 Water issues intensified by climate change and human activities

Many studies have shown that global warming is intensifying global energy and hydrologic cycles. Thus, major impacts can be expected on the hydrologic cycle, freshwater availability, and water demands in China. Global climate change is likely to increase the number of intense precipitation days and flood frequencies in the northern hemisphere and snowmelt-driven basins. In more arid settings, the frequency and severity of droughts are expected to worsen as a result of regional decreases in total rainfall, causing more frequent and longer dry spells and greater water losses through evapotranspiration at high temperatures.

Extensive infrastructure for water resources control, including dams and reservoirs, as well as large systems for inter-basin water transfer, have contributed significantly to the effective management of surface water. However, these projects themselves have given rise to a variety of new environmental problems. For example, the construction and operation of hydroelectric projects may contribute to a loss of biodiversity through landscape alteration,disruption of critical fish migration routes between downstream floodplains and upstream tributaries, salinization of soils in regions around reservoirs due to rising groundwater levels, and finally, through saline water invasion in estuary regions due to a decline in discharges from the impoundment of freshwater in reservoirs.

4 Way forward: Opportunities and prospects

Floods, droughts, and water pollution are impediments to the sustainable development and management of water resources in China. Hydrological science is playing an increasingly vital role in understanding these problems and in finding appropriate solutions. To better understand the flood and drought events in China, hydrologists need to adopt systems-based approaches to study the energy balance and water cycle at different temporal and spatial scales. Progress will require research on topics such as (1) fundamental characteristics of the hydrologic cycle at different temporal and spatial scales, (2) the inherent associations between climate variability and hydrological change, (3) hydrological consequences of human activities, (4) engineering and non-engineering measures for flood control and drought mitigation, and (5) the socioeconomic aspects of water resources management.

Considering the shortages caused by the uneven distributions of water resources and pollution, water conservation and improvements of water use efficiency in agriculture and industry will emerge as the most effective and sustainable solutions. China should develop integrated water resources management and efficiency plans based on interagency and multidisciplinary approaches. Emphasis should also be placed on the development of alternative water supplies, such as seawater and municipal wastewater, when financially possible and technically feasible. Other important foci for hydrological research include climate change impacts on water resources, flood and drought forecasting and prevention, and environmental assessment of water resources development projects (such as the Three Gorges Dam and the South-to-North Water Transfer Project). China should also begin planning to ameliorate the consequences that global warming could cause on its water resources infrastructure and should build resilience against future uncertainties.