The articles we read in Europe about the Three Gorges Dam are often critical or even negative. In particular, it is feared that the dam has upset the balance of the natural environment. Criticism has also been leveled at the fact that the project necessitated the resettlement of more than 1 million people. Reports praising the positive effects of the dam are rare.

In most cases, assessments of the project are based on a very specific and sectorial perspective. However, it is essential that the impact of the dam be considered from a broader perspective.

Taking a more holistic view, the catchment area of a river resembles a tree. The cities in this river basin form its "fruit". The aim of maintaining this "tree" is to obtain fruits of high quality. So the aim of managing a catchment area is to obtain cities with a good standard of living.

The Yangtze is the longest river in China and the third longest river in the world. Although its catchment area accounts for less than one fifth of the territory of China, it is responsible for feeding one-third of the population. Hence, it affects not only the lives of the approximately 400 million people in its catchment area but also the socioeconomic development of the entire country.

The idea of attenuating the extreme flow rates of the Yangtze through the construction of an artificial lake in the area of the Three Gorges arose as far back as 1921. However, the knowledge and technology available at the time prevented the successful planning of such an ambitious project. It was not until 1954 that progress in science and technology enabled the concrete planning of the project to be initiated, and construction commenced in 1994 following careful clarification of the details.

The dam was conceived as a multipurpose installation from the outset. In addition to the main aim of influencing runoff activity, that is the retention of flood peaks to protect the downstream regions, the project also involved hydropower generation, the improvement of shipping capacity and the provision of water for irrigation systems.

With the construction of the Three Gorges Dam, an artificial lake was created which is 600 kilometers in length and 1.1 km wide on average. Since the completion of the project, 22 billion cubic meters of water storage is available for flood retention during the critical season.

In addition to improving flood protection, the far-sighted design of the dam also enables the exploitation of hydropower production. The 32 turbines can be used to generate 88.2 terawatt hours of electrical energy a year. This is more than twice the amount of electricity produced by all of Switzerland's hydropower plants. This form of energy generation saves on the burning of several million metric tons of coal each year. There is no question that this saving has a very positive impact on the air quality and the reduction of China's carbon dioxide emissions.

Thanks to the generous design of the locks and the increase in the water level in the gorge area through the damming of the Yangtze, the annual shipping capacity has been increased by a factor of five and the transport costs reduced by 35 percent. Other forms of freight transport, such as rail or road, put a greater burden on the environment.

In the event of drought, the storage capacity of the Three Gorges Dam makes it possible to increase runoff when levels are too low. This is particularly important as droughts are becoming increasingly severe due to climate change.

The exploitation of the possibilities offered by the Three Gorges Dam promotes the quality of the fruit from this tree of life, raising the standard of living in the cities in the region.

But despite all the advantages, it must not be forgotten that the construction of the dam required the resettlement of millions of people. It is easy to understand how difficult it was for farmers to move from the land worked by their ancestors. However, their sacrifices were worth it to save the fruits of the entire tree.

The Three Gorges Dam was a necessary precondition for the improvement of the quality of life in a large part of the Yangtze catchment area. Necessary does not, however, mean sufficient: the control of the lake water level and, therefore the way in which the flow is regulated, is crucially important to guaranteeing the positive effects of the dam. Due to development and global warming, it may be assumed that this flow regulation will become a more complex task and that additional artificial lakes will also be required.

Sustainable management is not possible without a very good evidence base and clear flood regulation criteria. Although the management of the flood in 2011 showed that the current regulation was successful, it is essential that the criteria be subject to constant assessment and that the instruments used be constantly improved and adapted to meet changing requirements.

The author is vice-director of Swiss Federal Office for the Environment, and president of National Platform for Natural Hazards.