藏北牧区地表湿润状况对气候变化的响应

利用1961～2006年藏北牧区6个站月平均最高气温、最低气温、降水量、风速、相对湿度、日照时数资料,应用Penman-Monteith模型计算得出潜在蒸散,分析了地表湿润指数的变化趋势、年代际变化特征及季节差异,并讨论了影响地表湿润指数的气象因子.研究表明:近46a藏北牧区年地表湿润指数呈现增大趋势,增幅0.01～0.05/10a;四季地表湿润指数大部分牧区也呈增大趋势,春、秋季增幅明显.近26a(1981～2006年)、季潜在蒸散表现为明显的减少趋势,降水量显现增多趋势,地表湿润指数增大趋势加大,以夏季最为突出.就年平均而言,藏北牧区20世纪60年代初、中期以高湿低温为其主要气候特征;20世纪60年代后期至80年代中期,表现为冷干型的气候特征;90年代初之后,气温持续升高,地表湿润指数显著增加,呈现以暖湿为主的年代际变化特征.湿润指数对降水量、相对湿度和气温日较差的响应最为敏感,而对日照时数和风速的响应也较为明显.

Responses of climatic change on surface humid index in Northern Tibet during the period of 1961-2006

Based on the observational data of monthly maximum temperature, minimum temperature, precipitation, wind speed, relative humidity and sunshine duration of 6 stations in the Northern Tibet from 1961 to 2006, the potential evapotranspiration were computed using Penman-Monteith equation. The linear trend, inter-decadal variation and the seasonal difference of the surface humid index were analyzed, and the relationship between surface humidity index and elements such as sunshine duration, mean wind speed and diurnal temperature range were discussed. The results show that: (1) The annual surface humidity index increased during the period of 1961-2006, and the increase rate was around 0.01-0.05/10a. Also, the seasonal surface humidity index increased in most parts of the Northern Tibet, especially in spring and summer. In recent 26 years (1981-2006), the annual and seasonal potential evapotranspiration showed a declining tendency, and precipitation plays an obvious increasing trend, which resulted in the rise range of annual and seasonal surface humidity index increase, especially in summer. (2) In terms of inter-decadal variations for surface humidity index, from the early to mid 1960s, the climate showed higher wet and lower temperature in the Northern Tibet. While from the late 1960s to the mid 1980s, the climate presented colder and drier. After the early 1990s, the increasing trend of mean temperature existed, the surface humidity index increased significantly, and the climate showed warm and wetter. (3) The surface humidity index was most sensitive to precipitation and relative humidity as well as daily temperature range change, which was more sensitive to sunshine duration and wind speed change.