China's second-longest river has for centuries been referred to as "China's Sorrow" because of the millions of people killed in disastrous flooding. These days, it manages still to offer the potential for devastating seasonal floods, while also suffering from too little water the rest of the time.
Over the next week, the Yellow River is set to break the record for the number of days during which it has run completely dry along its lower section, leaving farmland parched and threatening the autumn's harvest.
Rising high upon the Qinghai plateau in western China, the Yellow River - in reality an orange-brown colour - is a 3,000-mile lifeline through eight provinces before reaching the Bohai Sea off Shandong Province. Some 180 million people live along its path.
The problem is that for several months of the year the river now dries up hundreds of miles before it gets anywhere near the sea. And the dry periods are getting progressively longer; last year's record of 136 dry days in the lower reaches is about to be broken, threatening the livelihoods of 52 million people and seven million hectares of crops, the China Daily said this week. This year the dry river bed has reached further than ever, all the way up into Henan province. Just 20 years ago, the dry river period in Shandong would normally last only a couple of weeks or so.
At the Qinghai Province Weather Modification Centre, in Xining city, the rain engineers have taken direct action this year, for the first time turning their rain-making arsenal towards the skies above the headwaters of the Yellow River. Six years of below-average rainfall in north-west China has reduced the inflow into the upper reaches of the river, exacerbating the problems caused further downstream where the flow is being exhausted by the increased irrigation and industrial demands of a growing population.
The rainmen of Qinghai sit before a row of computers showing cloud densities and air flow patterns above the mountains of Qinghai as they decide whether or not to strike. Zhao Shixiong, the senior engineer, is on the lookout every day during spring and summer for dense cloud at least 2.5km thick. "I read all this data and see all the conditions are met, and then I can send the aircraft," Mr Zhao said.
Between April and mid-June this year, Mr Zhao despatched aircraft six times to the skies above the upper reaches of the Yellow River, armed with liquid nitrogen. They sprayed it inside the clouds to create small ice droplets which fell as rain. From late June, they switched to using land-based anti-aircraft guns, which fired silver iodide crystals into the clouds to seed the rainclouds. As a result of these onslaughts, there was an estimated net inflow of man-made rain into the Yellow River of 260 million cubic metres, about 1.2 per cent of the river's annual flow in Qinghai.
Until this year, Qinghai's rain-making had taken place only above its eastern farmlands, to water the crops which often died because of lack of natural rain. The new target clouds above the upper reaches of the Yellow River were not, however, assaulted out of benevolence for downstream compatriots. The pilot 1 million yuan (pounds 77,000) project was financed by the Qinghai electricity Bureau, worried about falling water levels behind the dam at Qinghai's Longyangxia hydro-electric station.
It is not, sadly, within the powers of the Qinghai rainmen to solve the problems of the Yellow River. The Chinese government has belatedly woken up to the need to encourage water conservation, and the search is also on in north-west China for viable new underground water supplies. In the most ambitious plan, one massive scheme has been mooted to divert water northwards from the upper reaches of the Yangtze River hundreds of miles through vast tunnels and aqueducts into the Yellow River. Whether such an expensive engineering project ever gets off the drawing board remains to be seen.
For the time being, Mother Nature still has the final laugh. The amount of water coursing through the Yellow River is much less than in earlier decades, but the river level is considerably higher because of the huge amounts of silt deposited on the river bed. The height of the river therefore rises by about 10cm a year, and in the northern China plains it flows high above the surrounding land, held back by 800km of artificial dikes. The possibility of unusually heavy rains, or a breach in a large dike, means that vast areas are short of water for much of the year but also live under threat from devastating seasonal floods.
While millions of farmers along the Yellow River are hit by drought every year, the Chinese government must still spend vast sums of money on flood prevention schemes along the river. To this end, it plans to construct more than 20 dams along the waterway over the next three decades.
For 57-year-old Mr Zhao and his rain-makers, it all too often seems like a cruel joke. Just hours after he showed off his computers to The Independent and explained that as the crops were being harvested rain was not wanted, the heavens opened above eastern Qinghai; a torrential downpour started and did not stop for two days.