1982-2014年青藏高原地表蒸散量时空分布及其变化影响因子分析

摘要

蒸散是地球水循环的关键驱动因子,是地表水平衡和能量平衡的重要分量,因而也体现生态系统水文调节局地热调节功能;青藏高原是长江和黄河等重要河流的发源地,该区域水量平衡对区域生态安全具有重要意义.本文对全球尺度发展的遥感蒸散双源模型ARTS,利用涡度相关观测数据进行验证和评价,以空间插值的气象数据,卫星遥感的FPAR和LAI等驱动模型,估测1982-2014年间青藏高原实际蒸散ET,分析其年际和季节动态变化特征,并采用敏感性分析法和多元线性回归分析计算各气象因子变化对蒸散量变化的贡献率,探讨影响青藏高原蒸散量变化的主导因素.结果 表明:(1)估测值能解释观测值季节变化的80％以上(复相关系数R2=0.80,显著性水平P＜0.001),表明模型具有较高的估算准确度.(2)近30多年全年、春、夏和秋季影响蒸散年际变化呈显著增加趋势;但变化趋势存在显著的区域分异,全年或夏季藏南河谷地区呈显著降低趋势(每10年降低20 rnm以上),而阿里、拉萨河谷、青海海北地区则为增加趋势(每10年增加10mm以上).(3)敏感性分析和多元线性回归分析均表明,年际变化趋势的主导因素是气候变暖,其次是降水的不显著增加;但植被变化的影响也较大,与气候因子共同能够解释蒸散趋势的56％(多元线性回归方程R2=0.56,P＜0.001);低覆盖草地多年蒸散分别是高、中覆盖度草地的26.9％和21.1％.青藏高原在显著变暖、不显著变湿的气候变化背景下,地表蒸散的增加必以冰川融水为代价而威胁区域生态环境安全,如何保护生态,维持区域社会可持续发展是难题和巨大挑战.%Evapotranspiration is the key driving factor of the earth's water cycle,and an important component of surface water and energy balances.Therefore,it also reflects the geothermal regulation function of ecohydrological process.The Qinghai-Tibet Plateau is the birthplace of important rivers such as the Yangtze River and the Yellow River.The regional water balance is of great significance to regional ecological security.In this study,ARTS,a dualsource remote sensing evapotranspiration model developed on a global scale,is used to evaluate the actual evapotranspiration (ET) in the Qinghai-Tibet Plateau from 1982 to 2014,using meteorological data interpolated from observations,as well as FPAR and LAI data obtained by satellite remote sensing.The characteristics of seasonal,interannual and dynamic changes of evapotranspiration were analyzed.The rates at which meteorological factors contribute to evapotranspiration are calculated by sensitivity analysis and multiple linear regression analysis,and the dominant factors affecting the change of evapotranspiration in the Qinghai-Tibet Plateau are discussed.The results show that:(1) The estimated values can explain more than 80％ of the seasonal variation of the observed values (R2 =0.80,P ＜ 0.001),which indicates that the model has a high accuracy.(2) The evapotranspiration in the whole year,spring,summer and autumn show significant increasing trends in the past 30 years,but have significant regional differences.Whether in the whole year or in summer,the southern Tibetan Valley shows a significant decreasing trend (more than 20 mm per 10 years),while the Ali,Lhasa Valley and Haibei areas show increasing trends (more than 10 mm per 10 years).(3) Sensitivity analysis and multiple linear regression analysis show that the main factor driving the interannual change trend is climate warming,followed by the non-significant increase of precipitation.However,vegetation change also has a considerable impact,and together with climate factors,it can explain 56％ of the interannual variation of evapotranspiration (multiple linear regression equation R2 =0.56,P ＜ 0.001).The mean annual evapotranspiration of low-cover grassland was 26.9％ of high-cover grassland and 21.1％ of medium-cover grassland,respectively.Considering significant warming and insignificant wetting in the Qinghai-Tibet Plateau,the increase of surface evapotranspiration will threaten the regional ecological security at the cost of glacial melting water.Effectively protecting the ecological security and maintaining the sustainable development of regional society are difficult and huge challenges.