Clare Nuttall in Astana -

Tajikistan says it will wait for the results of an independent study before starting to build the world's tallest dam at the Rogun hydropower plant. Even so, it is likely to press on with construction whatever the result of the study, inflaming tensions in an already jittery region where water is an increasingly precious resource and earthquakes a constant worry.

Relations might be tested sooner. Part of Tajikistan's controversial Rogun hydroelectric power plant could be put into operation in the very near future before the dam is built. In August, Tajik state television showed engineers at Rogun saying that the first two units of the hydro plant could be put into operation using low-pressure water, and work to block the Vakhsh river, a tributary of the Amu Darya, has already started, according to local press reports.

For the dam, Dushanbe has agreed to wait for an expert assessment of Rogun's social and environmental impact commissioned by the World Bank, in the hope of securing finance from international financial institutions. However, Uzbekistan, the fiercest opponent of the project, claims that construction is already underway.

Tajikistan's autocratic leader, President Emomali Rakhmon, appears determined to go ahead with the dam, appealing to Tajik nationalism as he tries to raise funds from the impoverished population. In an address to the parliament on April 26, Rakhmon pointed out that power shortages are scaring investors away. "Who wants to invest in a country that experiences acute power shortages during six months of the year?" he asked rhetorically, Asia Plus reported. Tajikistan's largest enterprise, the Tajikistan Aluminium Company (Talco), also relies heavily on cheap power.

Not very neighbourly

The plans have caused a serious rift between Tajikistan and Uzbekistan, which lies downstream on Central Asia's two great rivers, the Amu Darya and Syr Darya. This threatens to disturb the fragile balance of water management that has existed between the five Central Asian republics since the breakup of the Soviet Union. Uzbekistan also claims such construction is foolhardy in an earthquake-prone area.

Uzbekistan periodically uses the threat of cutting off gas supplies to its upstream neighbours to deter them from letting too much water through their dams in winter, which causes flooding and reduces the amount of water available for irrigation. The failure to renew the gas export agreement between Uzbekistan and Tajikistan this year has been a further incentive to Tajikistan to pursue hydropower investments. Dushanbe has also accused Uzbekistan of holding up rail freight at the border in an attempt to force the Tajik government to abandon its construction plans. In early 2012, the Tajik embassy in Moscow warned these tactics had pushed Tajikistan to the brink of a "humanitarian crisis".

Uzbek officials have gone so far as to warn that Rogun could cause war to erupt. In more conciliatory moments, they have appealed to Dushanbe to build smaller dams instead, though such appeals have fallen on deaf ears, perhaps because Rakhmon regards the giant dam as a monument to his rule as much something that will benefit the population. "The question of Rogun is too often politicised. The impact depends on the scale of the dam. The smallest size being considered would have no effect on Uzbekistan, the medium has very little effect, and there might be some effect from the largest size," says Kai Wegerich of the International Water Management Institute. "Uzbekistan's fear is that Tajikistan will release water only in the winter, but this is not correct, because Tajikistan is more diversified in terms of industry, and wants to benefit from selling electricity to Pakistan in summer."

Water is a huge issue in Central Asia, where five states, all with fast-growing populations, depend on shared resources. In the 1960s, a fatal decision by the Soviet government to prioritise cotton production over the Aral Sea fishing industry resulted in the massive diversion of the Amu Darya and Syr Darya, causing the Aral Sea - a lake lying between Kazakhstan in the north and Uzbekistan in the south - to lose around 60% of its volume between 1963 and 1987. Salt and sand storms have destroyed surrounding agricultural land, and had devastating consequences for the local population's health.

Not deterred by causing the world's greatest manmade disaster, Soviet planners continued to mull plans to divert the Ob and other Siberian rivers from the Arctic Ocean to the Central Asian cotton fields. The idea was dropped when the Soviet Union started to disintegrate, but even recently top officials including Kazakhstan's President Nursultan Nazarbayev and Uzbekistan's Islam Karimov have refloated the idea.

Dam the status quo

Since the breakup of the Soviet Union, the five Central Asian states have used a complex web of agreements, and regular ministerial-level meetings, to share the region's limited water resources. Each state has a quota for water use, similar to those allocated during the Soviet era. "Central Asia's water resources are very heavily used, even over-used. Water sharing works in years with normal or above normal flow, but things get tense in low flow years. Everybody has to cut back when there isn't enough water," says Philip Micklin, author of "Desiccation of the Aral Sea: A water management disaster in the USSR". There is also conflict within states, when powerful regional leaders take more than their share.

However, the massive scale of the Rogun dam threatens to disturb the status quo in a way that the ongoing bickering over water sharing and Kyrgyzstan's more modest construction plans have not.

Despite the angry rhetoric, the high level of Russian engagement - including military bases in Kyrgyzstan and Tajikistan - makes armed conflict between the states unlikely. Following Putin's visits to the region in 2012, Moscow has ensured its long-term military presence in both countries.

Russia has also latched onto the water issue, providing funds for the pro-Moscow government of Almazbek Atambaev in Kyrgyzstan to build the Upper Naryn Cascade and Kambarata-1 hydropower plants. Russia also plans to provide $500m for the CASA-1000 project to build an electricity transmission line from Central Asia to Afghanistan and Pakistan.

However, Moscow has stopped short of financing Rogun, a decision likely based on the incendiary effect this would have on relations with Uzbekistan. Instead, shortly after his 2012 visits to Central Asia, Putin invited Kazakhstan and Uzbekistan to join the Kyrgyz hydropower projects in an attempt to resolve water use disputes.

The other superpower vying for influence in Central Asia, China, has already helped rebuild Tajikistan's dilapidated roads, but again no concrete offers to support Rogun appear forthcoming. Despite its own controversial domestic projects such as the Three Gorges Dam, which displaced 1.2m people, Beijing seems reluctant to take a similar step in Central Asia. While state-owned SinoHydro is active in Tajikistan, the company backed off from a project to build a dam on the Zerafshan river after opposition from Tashkent. With both Uzbekistan and Turkmenistan now supplying gas through the Central Asia-China pipeline, support for Rogun is looking less likely.

Even without deliberate provocations, there are other factors contributing to increased pressure on the Central Asian region's limited water resources, and threatening to raise tensions.

All five republics have expanding populations, as does Afghanistan, the fourth state in the Amu Darya river basin. Soviet concerns that Kabul could also demand its share of the river's waters were never realised due to the outbreak of war, but if north Afghanistan remains stable, there could be more competition within the Amu Darya basin. To the east, China's fast-developing Xinjiang region is also increasing water use.

The consequences of climate change are already being felt in Central Asia, where temperatures are steadily rising and weather patterns becoming less predictable. The glaciers that feed the Amu Darya and Syr Darya rivers are shrinking by a rate of between 0.2% and 1% a year, which in the long-term will result in a significantly lower flow of water to be shared among the five states.

Despite being aware of the climate change threat, the region's governments have not yet banded together to tackle the issue. "The countries are still trying to be independent, and because of this mindset, it is difficult to face the question and say that in the end they need each other. Only after they satisfy their mission to be independent, can they decide to integrate again," Wegerich says.

For the time being at least, Central Asia's water problems show no signs of improving, with the need for the regions' governments to find a practical solution to sharing limited resources often overshadowed by both economic need and nationalistic posturing. Rogun and other new projects are putting more pressure on an already difficult situation.