Gansu
Gansu Geography & Climate
Geography
Gansu is shaped like a bone, some 1,600 kilometres from end to end and in places barely wide enough for a road and a railway, and that shape is entirely dictated by the terrain around it.
The Hexi corridor
Between the Qilian mountains to the south and the Gobi and Badain Jaran deserts to the north lies a narrow passage of relatively flat ground. Meltwater from the Qilian glaciers runs north into the desert and creates a string of oases — Wuwei, Zhangye, Jiuquan, Dunhuang — each a green patch in gravel desert, and each a stage on the Silk Road. The corridor exists because those rivers do.
Desert
North of the corridor the Gobi and the Badain Jaran, the latter holding the tallest stationary sand dunes in the world at over 400 metres.
The Danxia landforms
At Zhangye, red sandstone and mudstone laid down in alternating layers over millions of years were tilted by the uplift of the Tibetan plateau and then eroded, exposing the strata as bands of colour running across the hillsides — rust, ochre, cream and a greenish grey from different mineral content.
South and east
The Tibetan plateau edge in the south-west, with grassland above 3,000 metres, and the loess plateau in the east around Lanzhou, deeply gullied and prone to landslides.
Crescent Lake
A spring-fed crescent of water lies among the Mingsha dunes outside Dunhuang and has done for at least two thousand years, which should not be possible — the dunes are mobile and the desert is one of the driest places in China. The prevailing wind circulates within the bowl in a way that carries sand back up the slopes rather than into the water. Groundwater extraction shrank it badly in the twentieth century and recharge schemes have since partly restored it.
The Yellow River
Cuts through Lanzhou, the only provincial capital the river passes directly through.
Climate Patterns
Gansu is dry, sunny and extreme, and the numbers vary enormously along its length.
The corridor
Dunhuang receives around 40 millimetres of rain a year — among the driest inhabited places in China. Summers are hot, above 35°C, and winters fall well below freezing. The daily range is large in every season: a thirty-degree afternoon in the desert can be followed by a night near zero, and layers matter more than a single warm coat.
The southern plateau
Xiahe sits near 3,000 metres and is cold, with snow from October and hard frosts into May. Even in July the nights are cold, and the sun at that altitude is fierce.
The loess east
Around Lanzhou, a continental climate with hot summers, cold winters and summer rain, and a persistent air quality problem — the city sits in a narrow river valley between hills that traps pollution, and it has historically been among the worst in China for it, though conditions have improved.
Wind and dust
Spring brings dust storms off the Gobi that can turn the sky orange and close roads, and the corridor is windy throughout.
Why the paintings survived
The dryness is the reason Mogao exists as it does. Pigment, silk and paper that would have rotted in a monsoon climate within a century survived for over a thousand years in air that holds almost no moisture, which is also why the sealed library cave preserved fifty thousand documents intact. It is equally why modern visitor humidity is treated as a serious threat and numbers are capped.
Sun
Very high UV across the province, extreme on the plateau.