呼伦贝尔植被蒸散发时空变化研究

［目的］蒸散发是影响陆地和大气系统能量交换过程的关键因素，也是评价陆地生态系统的重要指标。文章运用中分辨率成像光谱仪(MODIS MOD16A2和MOD13A1)产品数据，并结合中国气象数据共享网的气象数据，估算了2008—2017年呼伦贝尔植被的蒸散发量，并在年度和季节两个时间尺度开展了植被蒸散发时空变化分析。［方法］运用变异系数(CV)和突变检验法(Mann Kendall），研究2008—2017年呼伦贝尔地区年际和季节蒸散发时空变化趋势。使用Pearson相关分析法，对呼伦贝尔地区季节尺度的蒸散发与归一化植被指数(NDVI)、各气象要素进行相关分析。［结果］2008—2017年呼伦贝尔地区蒸散发呈上升趋势，蒸散发值较大的月份为3月、8月和11月，蒸散发主要集中在5—10月份。变异系数的空间分布较均匀，平均变异系数为038，变异系数变化幅度较大的区域主要集中在呼伦贝尔北部，CV值均在1～265。CV变化幅度较小的区域主要分布在呼伦贝尔中部和南部，CV值在041～084。从年际变化趋势来看， 2013年为一个蒸散发突变年； 根据呼伦贝尔月份变异系数的计算，从1—12月变异系数幅度变化较大，说明呼伦贝尔ET变异剧烈。呼伦贝尔月份平均CV值是1，草原区的CV平均值是096，森林区的CV平均值是104，农区的CV平均值097。植被蒸散发与气象要素关系分析表明：蒸散发与气温、水汽压、NDVI、降水、日照时数呈显著正相关关系。［结论］2008—2017年呼伦贝尔地区蒸散发总体呈上升趋势，从整个季节变化来看，蒸散发起伏变化趋势明显，波动变化较大。从空间分布上来看，总体表现为呼伦贝尔南部的蒸散发大于北部。蒸散发主要集中在4—10月份，多年的低值出现在5月。不同区划类型平均蒸散发量由大到小依次为草原区＞农区＞森林区，全区的蒸散发变化趋势与农区变化趋势较为一致。正相关性强度依次为气温＞日照时数＞NDVI＞水汽压＞降水＞风速。

ANALYSIS OF TEMPORAL AND SPATIAL VARIATION OF VEGETATION EVAPOTRANSPIRATION IN HULUN BUIR

Evapotranspiration is one of the key factors affecting energy exchange between terrestrial and atmospheric systems, and also an important index for evaluating terrestrial ecosystems. In this study, the evapotranspiration of Hulun Buir vegetation from 2008 to 2017 was estimated by using MODIS MOD16A2 and MOD13A1 product data in combination with the meteorological data from China Meteorological Data Sharing Network, the spatial and temporal patterns of vegetation evapotranspiration were then analyzed at the annual and seasonal scales. The temporal and spatial trends of evapotranspiration in Hulun Buir from 2008 to 2017 were studied by using coefficient of variation and Mann Kendall test methods, and pearson correlation analysis was used to analyze the correlation between evapotranspiration, NDVI and meteorological factors at the seasonal scale in Hulun Buir. Evapotranspiration in Hulun Buir had increased from 2008 to 2017. The largest evapotranspiration was recorded in March, August and November, and most of evapotranspiration concentrated from May to October. The average coefficient of variation was 0.38. Large variation were mainly located in the north of Hulun Buir, with CV values ranging from 1 to 2.65. The smaller CV were mainly located in the central and southern Hulun Buir, with value ranging from 0.41 to 0.84. A sudden change in the evapotranspiration was recorded in the year of 2013. The great monthly variation coefficient of Hulun Buir ET indicated that a strong fluctuation change in Hulun Buir ET. The monthly average CV value of Hulun Buir area was recorded as 1.The CV across the grassland, forest, agricultural areas averaged 0.96, 1.04, and 0.97, respectively. The results showed that evapotranspiration was positively correlated with temperature, water vapor pressure, NDVI, precipitation and sunshine hours. The annual evapotranspiration in Hulun Buir showed an increasing trend from 2008 to 2017, and the evapotranspiration fluctuated obviously as the seasonal variation. The evapotranspiration in the south of Hulun Buir is larger than that in the north. Evapotranspiration mainly occurs from April to October, and the lowest value for many years appears in May. From largest to smallest, a list of land use types ranks by the average evapotranspiration is grassland area, agricultural area, and forest area. The trend of evapotranspiration in the entire region is consistent with that in the agricultural area. The ranked order by positive correlation factors are temperature, sunshine hours, NDVI, water vapor pressure, precipitation and wind speed.