西藏近35年地表湿润指数变化特征及其影响因素

Climatic change of terrestrial surface humid index and its impact factorsover Tibet in recent 35 years

中文关键词:  最大潜在蒸散，地表湿润指数，影响因子，变化趋势，西藏高原

英文关键词:Maximum potential evapotranspiration, Surface humid index, Impact factor, Linear trend, Tibet Plateau

中文摘要:

      利用1971—2005年西藏25个气象站月平均最高气温、最低气温、风速、相对湿度、日照时数、降水量等资料，应用Penman Monteith模型计算了最大潜在蒸散、地表湿润指数，分析了其空间分布、年际变化特征及季节差异，并讨论了影响地表湿润指数变化的气象因子。研究表明：近35年，西藏年降水量表现为显著的增加趋势，增幅为15.0 mm/(10 a)；年最大潜在蒸散呈不同程度的减小趋势，为-4.6—-71.6 mm/(10 a)。阿里地区西南部、聂拉木年地表湿润指数为不显著的减小趋势，其他各地均呈增大趋势，增幅为0.02—0.09。就西藏平均而言，年地表湿润指数以0.04/10 a的速率显著增大，尤其是近25年增幅更为明显。各季节地表湿润指数也表现为增大趋势，以夏季增幅最明显。20世纪70年代到80年代主要表现为以低温低湿为主的年际变化特征，进入90年代后，气温持续升高，地表湿润指数明显增加，呈现出暖湿型的气候特征。降水量和相对湿度的明显增加，以及平均气温日较差的显著减小是地表湿润指数显著增加的主要原因，平均风速和日照时数的明显减少，在湿润指数增加趋势中也起着重要作用。

英文摘要:

      Based on 25 observational station's data of monthly maximum temperature, minimum temperature, precipitation, wind speed, relative humidity and sunshine duration over Tibet from 1971 to 2005, the data of the maximum potential evaporation was computed by Penman Monteith Model. The surface humid index is the ratio of rainfall to maximum potential evapotranspiration (ET0). The distribution, inter-annual change and the seasonal difference of ET0 and surface humid index were analyzed, also the impact climatic factors for the change trend of surface humid index were discussed. The main results were as follows: In recent 35 years, the annual precipitation trend increased significantly and the rate of increasing was 15.0 mm/(10 a) in Tibet, the respective decreasing trend of annual ET0 was prevailing and its decrease were -4.6--71.6 mm/(10 a). The decrease of annual surface humid index was insignificant in southwestern Ngari district and Nyalam county, annual surface humid index was increasing at the rate of 0.02-0.09/(10 a) in others district of Tibet. On an average in Tibet, the increasing trend of annual humid index was significant, and its increase was 0.04/(10 a), especially in last 25 years (1981-2005). Also, the increasing trend of seasonal surface humid index was overwhelming, particularly in summer. From the 1970s to the 1980s, the inter-annual characters behaved lower temperature and lower humidity. In the 1990s, the air temperature rose steadily, and surface humid index increased obviously. The phenomena indicated warm and wet climate over Tibet. It is thus obvious that the increase of the surface humid index is mainly caused by the remarkable increasing of precipitation and relative humidity as well as the significant decreasing of the daily temperature range, declining of the sunshine duration and wind speed may also played an important role in increasing of humid index.