近19年干旱半干旱过渡区气温降雨变化特征分析

针对西北干旱半干旱区生态环境各要素的过渡特性,文章以位于干旱半干旱典型过渡区的定西市为例,通过整理其地面观测站1991-2009年较为完整的气温和降水资料,分析了定西地区气温、降水的年平均变化趋势和年代际变化特征。结果表明:近19年来,年平均气温总体呈上升趋势,突变时间为1996年;年均降水量呈下降趋势,突变时间为1995年。造成定西气候变化的主要原因有:(1)定西市所处的地理位置和地形条件的汇聚特征,由其引起的焚风效应和夏季青藏高原上空下沉气流的影响,叠加近十几年定西地区人为活动温室气体排放量的增加,是引起地面温度增高主要原因。(2)定西地区处于印度洋、太平洋和欧亚大陆三大环流的汇聚位置,既受夏季青藏高原高空辐散气流的控制,还受全球尺度大气环流振荡的影响,高空环流脊槽移动转换和深浅变化会给当地带来大范围的干湿变化。温度升高地表蒸发加大也是影响当地降水减少的原因之一。

Analysis on Variation Characteristics of Temperature and Precipitation in Recent 19 Years in Arid and Semi-Arid Transition Region

Aim at the transition properties of ecological environment factors in Northwest arid and semi-arid areas,this paper take Dingxi City that located at the arid and semi-arid typical region as an example,by classify the data of temperature and precipitation collected from surface meteorological station from 1991 to 2009,the annual mean variation tendency of temperature and precipitation and the interdecadal variations are analyzed.The results showed that during recent 19-years,the Dingxi City’s annual mean temperature totally demonstrate a rising trend and the temperature mutation time is in 1995;annual mean precipitation display a falling trend and the precipitation mutation time is in 1996.The main reasons that cause Dingxi’s climate change as followed:(1)The foehn effect and the Tibetan Plateau sinking airflow in summer which are caused by the gathering characteristics of Dingxi’s geographical position and terrain conditions,superadd recent tens years the growth of greenhouse gas emissions due to human activity are the main reasons lead to the temperature increases.(2)The city is located in the gathering place of Indian and Pacific Oceans and Eurasia circulation,so,not only the summer Tibetan Plateau divergence airflow,but also the global scale atmospheric circulation oscillation influence Dingxi’s climate.In addition,upper air circulation ridge moving conversion and trough depth change will bring to the city a large-scale drought-wet change.Also,rising temperature,increasing surface evaporation are all the reasons for decreasing precipitation.