China Bets on Cloud Seeding to Boost Rainfall in Tibet and Xinjiang

23 May 2018 Andrew Thomson, Research Assistant, Global Food and Water Crisis Research Programme

Background

As the likelihood of severe drought threatens China’s water security, the Chinese Government is investing increasing amounts in cloud seeding infrastructure in its Western regions of Tibet and Xinjiang. According to the latest simulations by Chinese scientists, the Tibetan plateau, known as the “water tower of Asia”, is likely to experience severe drought in the coming decades, as natural rainfall fails to replace the water lost as a result of rising temperatures.

The prospect of reduced rainfall in this region is a daunting one, as the Tibetan plateau is the source of many major rivers, including the Yellow and Yangtze in China itself, and the Mekong, Salween and Brahmaputra, which each flow through several neighbouring countries. If those rivers are unable to provide a reliable source of freshwater, the livelihoods and, in some cases, the lives, of billions of people will be put at risk.

To prevent that, the Chinese Government is constructing a large network of cloud seeding chambers across Tibet and Xinjiang. Cloud seeding is a weather modification process where scientists use silver iodide to boost precipitation, thereby creating rain and snow. The process consists of:

  1. Chambers that burn solid fuel to release particles of silver iodide into the atmosphere
  2. The chambers are situated on steep mountain ridges facing monsoons from South Asia, as the monsoon hits the mountain, it produces an upward draft and sweeps the particles into the clouds
  3. The particles act as a nucleus and water vapour collects around them forming ice particles
  4. Ice particles then fall as rain or snow

The United Arab Emirates has successfully used cloud seeding to increase rainfall by ten to 15 per cent, according to the director of the UAE National Centre of Meteorology.

At the time of writing, a state-owned defence company has built 500 chambers for experimental cloud seeding in western China. A researcher involved with the project reported to the South China Morning Post that results so far were very promising.

Comment

Tibet and Xinjiang were selected as the the sites for cloud seeding infrastructure due to their importance in ensuring Chinese water security. Climate simulations predict that rainfall will steadily reduce in these regions over the coming decades, as a result of climate change. This has the potential to cause severe drought and reduced water flow in major Chinese rivers.

The large-scale construction of cloud seeding infrastructure is possible as both Tibet and Xinjiang border the Himalayas. The numerous mountain ridges make the region a favourable site for tens of thousands of cloud seeding chambers.

Chinese officials estimate that ten billion cubic metres of additional rainfall will be produced annually from cloud seeding, equal to roughly seven per cent of the water consumed in China, over an area the size of Alaska in China’s arid western regions. As well as mitigating the effects of climate change, the added rainfall is expected to prompt further economic development in Xinjiang and Tibet. An increase in rainfall would revitalise the agricultural sector and make these dry regions more hospitable, attracting both tourists and settlers.

Despite the seemingly miraculous benefit of cloud seeding technology, there are some problems that could have harmful effects on the environment. The process of cloud seeding involves releasing significant amounts of silver iodide into the atmosphere. Currently, silver iodide is not known to have any negative health effects on humans, animals or plants, but that could change if the concentration of the compound in the environment increases substantially.

There are also questions about the effectiveness of cloud seeding chambers and little evidence to guarantee that the scheme will work. Israeli scientists have questioned whether cloud seeding is an effective mechanism for inducing additional rainfall. Their claims are hard to dismiss, because it is difficult to prove a cause and effect relationship between cloud seeding and rainfall, due to the natural variability of rainfall patterns.

Despite those claims, there are over 80 cloud seeding projects in the world, with several increasing rainfall by a significant proportion. The most successful cloud seeding operations, however, are located in regions where there is already a large amount of water vapour in the atmosphere. That suggests that all cloud seeding is doing is simply causing the rain to fall in a targeted area, rather than creating additional rainfall.

If that is the case, cloud seeding could affect weather patterns in nearby regions. Forcing water vapour to fall in Tibet is likely to take out of the air water vapour that would have fallen as rain elsewhere. Cloud seeding could, therefore, have far-reaching consequences for local weather patterns, which could harm the fragile Chinese environment and also that of neighbouring countries.

Cloud seeding is a technology that has the potential to significantly improve water security, but for that potential to be realised, it must first be established as a safe and effective way to induce rainfall. The Chinese Government believes that it is and is counting on cloud seeding to increase rainfall in the water-distressed regions of Tibet and Xinjiang.

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