By Jonathan Watts, Guardian

It is hard to imagine a less fitting environment for a mollusc than the arid plain of Damoguzhen in southwest China.

There is not a drop of water in sight. The baked and fissured earth resembles an ancient desert. Yet shellfish are scattered here in their thousands; all so recently perished that shriveled, blackened bodies are still visible inside cracked, opened shells.

Far out of water, the aquatic animals are not the advance guard of evolutionary progress; but the victims of a drought that has devastated their habitat and now threatens the livelihoods of millions of people in surrounding regions. The Chinese government is so worried about the drought that it has embarked on a massive rain-making operation, involving firing thousands of shells and rockets into the sky to seed clouds.

Until last summer, Damoguzhen was home to a lake that stretched across a mile-wide expanse of water in Yunnan, a southern Chinese province famed for its mighty rivers, moist climate and beautiful views.

Today, it joins 310 reservoirs, 580 rivers and 3,600 pools that have been baked dry by a once-in-a-century drought that is evaporating drinking supplies, devastating crops and stirring up political tensions over dam construction, monoculture plantations and cross-border water management in southeast Asia. Linking specific weather events to human-caused climate change is impossible, but the drought is consistent with what climate scientists expect to see more of in future.

Hardest hit are local farmers such as Ying Yuexian, who has seen her tobacco and rice crop shrivel up over a six-month period that has seen record high temperatures and half the usual amount of rain.

"In February, the water dried up completely," said the 34-year-old, surveying the parched expanse where she once fished. "It turned into this overnight." Instead of drawing water from the lake, she now scrapes soil from its cracked bed in the hope that the nutrients can replenish the earth on her sun-blasted farmland.

Her husband, Zhu Chongqing, estimates that the family's annual income will halve this year and the situation could get worse because the wet season is not due for another month.

"We are waiting for the rain. We dare not plant rice or tobacco before that, but the drought continues" he said. "I've never experienced anything like this."

It is a similar story across the region. Older villagers say reservoirs and irrigation channels are dry for the first time in their lives. Mountain communities have to walk hours each day to secure drinking supplies. Rationing has been introduced in many areas, affecting more than 20 million people, 15 million animals and 2 million hectares of farmland.

With its mighty rivers and steep gorges, southwest China is the world's biggest hydro-electric powerhouse, but reservoir levels have fallen so low this year that 60% of dams report a decline in electricity output. This forces industrial estates and cities to burn more coal and emit more carbon to make up the shortfall.

Commodity values are also rising. In the giant rubber plantations of Xishuangbanna, farmers report a sharp fall in production that has pushed up prices by 40%.

"Less water means less rubber," said Zhang Xiaoping a rubber farmer. "In a good year, I can collect 80kg a day from these 300 trees, but I am down to half that now."

According to local media, sugar prices are up 10% because of the impact on cane fields. Rice and broad beans are also more expensive.

Wildlife is threatened because Yunnan — one of the most biodiverse regions on earth — is a last refuge for many species that are extinct elsewhere. Conservationists say birds have migrated, elephants moved to new territory and many big mammals are ranging further to secure water. Reptiles and plants are most vulnerable.

"We are hearing stories from nature reserves that amphibians are dying," said Wu Yusong of the Worldwide Fund for Nature's Yunnan office. "We are still in the process of monitoring the situation but we know that half the agricultural crops in this region cannot be harvested this year so we can imagine that other plants will be also be similarly affected."

The government says it has earmarked more than 7 billion yuan for relief projects, mobilized 7,600 water trucks and dug 180,000 wells to alleviate the impact.

It has also launched a massive weather modification operation. In a single week, the authorities fired over 10,000 silver nitrate shells and over 1,000 rockets into the clouds to induce rain, according to Zheng Guoguang, head of the China Meteorological Administration.

Short bursts of rain have mitigated the problem in some areas, but the overall picture remains grim and the causes contentious.

On stretches of the Mekong river, water levels are at 50-year lows, spurring criticism from downstream nations that China's hydropower expansion has siphoned off supplies that should be preserved for drinking water and fishing.

At the first summit this week of the Mekong River Commission, which comprises Thailand, Cambodia, Laos and Vietnam, the Chinese vice minister, Song Tao, insisted climate change rather than his country was to blame.