THE SEVEN SORROWS OF YUNNAN - Tambora: The Eruption that Changed the World - page 54

the last territories to be brought under the Chinese banner, the mountainous province of Yun-
nan in the southwest had long been integrated within the Indian Ocean trade zone and en-
joyed close cultural ties to the lands of the Mekong delta to the south: modern-day Burma,
Laos, and Vietnam. A key transit point along the ancient silk road, Yunnan has served as a
crossroads of cultures for millennia. 4 When the legendary Mongol emperor Kubla Khan sent
Marco Polo to the capital Kunming in the 1280s, the intrepid Italian marveled at its diversity
of peoples and religions. He also noted its abundance of rice and wheat fields, scattered across
some two thousand valleys nestled in the mountains. Despite its elevation and rugged topo-
graphy—the arable land is only 6% of its surface area—Yunnan is highly favorable to agricul-
ture thanks to these fertile, intramontane lowlands, called bazi , which range in size from less
than a kilometer to hundreds of kilometers across.
Until the disastrous upheavals of the nineteenth century, Yunnan enjoyed a more peaceful
history than might be expected given its geographical circumstance, perhaps on account of
its equable climate, which is likewise defined by convergence of differences.5 5 The extremes of
China's monsoonal climate are felt least in Yunnan, which acts as a buffer zone between the
spectacular Indian monsoon and the rival Asian monsoon that largely dictates China's weath-
er east of 105°E. The province's famously pleasant climate depends first on topographical dis-
couragement of the southwest monsoon out of the Bay of Bengal. These grandiose storms are
drained of their humid rage by their mountainous overland journey and enter Yunnan as no
more than a mild, encouraging breeze and scattered rain showers. In a normal summer, the
Tibetan plateau to the northwest—the “roof of the world”—acts as an enormous thermal en-
gine, driving heat upward and depressurizing the atmosphere. The scale of this Himalayan
warming is sufficient to offset even the effect of Yunnan's lofty elevation. In Kunming, T-shirts
are de rigeur at 1,500 meters above sea level. The southeast trade wind, too, an antiphon-
al presence, never fully yields to the Indian monsoon, ensuring that Yunnan experiences the
fewest summer gales of any region in China.
Yunnan is likewise spared the worst of winter's nick. Its mountains, running north-south,
act as a vertical shield against the prevailing cold-air masses spilling down from Mongolia.
The upward draw of the steep hillsides maintains a stationary high-pressure system, insulat-
ing the region like a meteorological version of the “pleasure dome” Coleridge imagined in
“Kubla Khan,” his opium-soaked fantasy of medieval China written in 1816. Even in Janu-
ary, the highland Yunnanese benefit from the thawing effects of southwesterly winds. Indeed,
Kunming enjoys the least variation in diurnal temperature anywhere in China: rarely below
10°C in winter or above 22°C at the height of summer. Awed by this moderation, Chinese
folklore has it that there is no summer or winter in Yunnan at all, only spring and autumn.