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西藏位于素有“世界屋脊”之称的青藏高原西南部,自然条件极其特殊:海拔高,平均海拔4 000米以上,山高且多无绿色植被;气压低,缺氧严重,平均含氧量和气压仅为海平面的60％;日照时间长,紫外线强烈,年日照时间为2 000～3 400小时。紫外线辐射强度较海平面高50％;降水少,气候寒冷、干燥。年平均降雨量在50～5000毫米不等,终年湿度小、蒸发大,年最高气温29℃,最低气温-45℃,昼夜温差达10℃～20℃;交通不便,交通以公路运输为主,兼有少量航空运输,无铁路运输。公路多蜿蜒在冰山雪地的高山峡谷之间。冬季遇有大风雪或雪崩,极易封山堵道。夏季雨量集中,易塌方断路,时有冰川解体,泥石流倾泻而下,淹没道路,冲垮桥梁,有的地段长达数月不能通行。
Tibet is located in the southwestern part of the Qinghai-Tibet Plateau, which is called “roof of the world.” Its natural conditions are extremely special: at an altitude of over 4,000 meters above sea level, with high mountains and no green vegetation; low atmospheric pressure, severe hypoxia, Air pressure is only 60% of the sea level; long sunshine time, strong ultraviolet radiation, the annual sunshine time of 2 000 to 3 400 hours. UV radiation intensity 50% higher than the sea level; less precipitation, the climate is cold and dry. Annual average rainfall in the range of 50 to 5000 mm, small annual humidity, evaporation, the maximum annual temperature of 29 ℃, the minimum temperature of -45 ℃, the temperature difference between day and night up to 10 ℃ ~ 20 ℃; traffic inconvenience, traffic mainly road transport, Both a small amount of air transport, no rail transport. Winding road in the snow-capped mountains and valleys. In case of snowstorm or avalanche in winter, it is easy to seal off the blockage. Concentrated rainfall in the summer, collapsing easily broken road, sometimes when the glacier disintegrated, debris flow pouring down, flooding the road, breaking the bridge, and some sections can not pass for months.