For Tibetan yak herder Bugye, the grassland in Nagqu prefecture, Lhoma County is much greener this year.

"The animals have more fresh grass, especially this summer," Bugye, 68, said, watching over his herd of 70 yaks and 200 sheep grazing under blue sky and bright sunshine this early autumn.

The rainy season came a month earlier and lasted longer. Herdsmen like Bugye, who endured a severe drought last year, were very pleased. But it is proving to be a mixed blessing.

Scientists consider this kind of weather fluctuation testimony of global warming and worry that herders will face more extreme weather conditions and degradation of the grassland in coming years.

An immediate consequence is that herders now face a severe shortage this winter of what is traditionally used for heating fuel- dried yak dung. With the prolonged rainy season, Bugye and other herding families have had trouble getting yak dung dried this year.

Each the size of an adult man's palm, dried yak dung is an indispensable fuel for herders in using cooking and heating during chilly winters.

The problem is so severe that the government of Tibet Autonomous Region is coming to their aid. Local meteorologists are tasked to keep a close monitor on weather in coming days, especially precipitation.

Bugye earns more than 40,000 yuan (US$5,840) a year selling his yaks and sheep. He and his nine-member family of three generations are well-off. They live in a brick house and use solar power, in addition to electricity from a power grid. Even so, Bugye's family needs at least 7,000 pieces of the dried dung to get through the winter. For other nomadic families who live in tents, the need is greater.

It is estimated that some 420,000 people living in Nagqu prefecture burn at least 2 million of dried yak dung one year.

"If the rain continues, it will result in a severe shortage of fuel for herders," said Tenzin Dondrup, deputy director of the Tibet Meteorological Bureau.

Winter on the Qinghai-Tibet plateau is particularly cold. What makes Tenzin even more worried is that there will be more snowstorms this winter. In past years, such as in 1998, more rainfall in the spring and summer has meant more snowstorms in winter, he said.

"I am very nervous about heavy snowstorms hitting the plateau this coming winter, especially when the herders have not prepared enough fuel, such as dried yak dung," he added.

According to the figures from Tibet Meteorological Bureau, the temperature on the plateau has risen 0.25 C every decade, about three times the global rate of temperature rising.

In Nagqu, the annual average temperature has risen by 0.6-1.5 C over the past 40 years. Annual precipitation has doubled from 78mm to 150mm over the same period, according to local weather records.

With an average altitude of 4,500m above sea level, Nagqu in northern Tibet is dubbed "the ridge of the roof of the world". Covering 446,000 sq km, the prefecture accounts for 37 percent of the autonomous region's territory.

Nagqu has the largest pastoral area, and the highest productivity in the region. Breeding livestock accounts for 70 percent of the prefecture's gross domestic product, and more than 90 percent of Nagqu residents make a living at it. It accounts for one-third of the region's animal husbandry.

But a chilly winter with fuel shortages and snowstorms are not the only consequences of global warming in this region. Flooding has also become a major threat.

After the Arctic and Antarctic, the Qinghai-Tibet plateau has the third largest number of glaciers. However, in the past 50 years, 82 percent of the plateau's glaciers have melted. The plateau has lost 10 percent of its permafrost layer in the past decade, according to the Chinese Academy of Sciences.

With the increased snow and glacier melt, the water levels of some 117 lakes in Nagqu alone have been rising. The water level of Tibet's second biggest lake, the Serling Co Lake, has risen 20 cm a year since 1997. At present, its water surface area reaches about 1,620 sq km. Compared with the coverage in 1997, the lake has expanded 5km to the west, 18km to the north, 23km to the southwest and 3km to the south.