唐代长安、洛阳作为都城和陪都的气候原因

本文从气候角度探讨唐代以长安为都城、以洛阳为陪都的缘由。唐代由于气候温暖湿润，降水量增大，水灾增多。洛阳因为经度地带性作用、降雨季节分配不均及洛阳河流的特殊情况。使得水灾情况比长安更严重：一是降水量大、水灾次数多，二是水势大、灾情重。尽管唐政府注意治水修堤坝，但中桥被冲毁、雨水断路乃至宫城被淹之事仍屡屡发生。长安虽然旱灾较洛阳严重，但水灾对都城的危害更直接、更严重，灭顶之灾的威胁使洛阳不宜作都城，所以建都长安。

On the Climatic Factor in Determining Chang An and Luo Yang as the Capital and the Alternate Capital Respectively in the Tang Dynasty

Since the climate in the Tang Dynasty was warm and humid,the amount of rainfall became much more than ever and floods increased.Affected by its latitude,unbalanced seasonal distribution of rainfall and its distinct rivers,floods in Luoyang were more serious and harmful than in Chang'an.First,the amount of rainfall in Luoyang was larger and the times of floods was more;second,the flow of water was higher and the effect of floods were more destructive.Although the Tang governments concerned about the construction of dams,such events as bridges,roads and even royal palaces being destroyed by great water often happened.Droughts did more severe harm to Chang'an than Luoyang,but in Luoyang it was flood which endangered the city more directly and intensely.The hovering danger of being drowned made Luoyang an inappropriate site for capital,so was Chang'an selected.