2000年至2008年松嫩平原生长季蒸散量时空格局及影响因素分析

蒸散是地表能量平衡与水量平衡的重要组成部分,研究松嫩平原生长季蒸散量时空格局及影响因素对该区农作物生长环境评价、水资源高效利用具有重要意义。本研究以MODIS产品为主要数据源,通过陆面能量平衡算法SEBAL及Penman-Monteith方程估算了松嫩平原2000年-2008年生长季(5月-9月)的陆面实际蒸散量,分析了蒸散量的空间分布特征及时间变化趋势,并在月时间尺度上通过基于像元的相关分析法探讨了蒸散量与主要气候因子(降水量、平均气温、平均相对湿度、平均风速、日照时数)相关性。结果表明:①除水体、沼泽湿地等高蒸散特性地物外,松嫩平原生长季蒸散量具有从西南部向东部、东北部逐渐增加的变化趋势,呈明显阶梯状变化,松嫩平原2000年-2008年生长季蒸散量的区域平均值呈明显下降趋势(P0.05),多年平均值为612.63mm,最大值(669.31mm)出现在2000年,最小值(570.79mm)出现在2005年;②受气候条件、土壤供水状态及植被覆盖度等因素影响,松嫩平原生长季各月蒸散量差异明显,7月蒸散最强烈,高达141.60mm,9月由于降水减少、气温降低,月蒸散量仅81.35mm;③对蒸散量与主要气候因子进行基于像元的相关分析得知蒸散量与降水量、平均气温的正相关性极其明显,而蒸散量与平均相对湿度的相关性在林地、水体分布区以负相关为主,在其他区域则以正相关为主,蒸散量与平均风速、日照时数的相关性相对较弱。

Analysis of Spatiotemporal Variations in Evapotranspiration and Its Influencing Factors over the Songnen Plain in the Growing Season during the Period 2000-2008

Evapotranspiration (ET) is a critical component of the land surface energy balancesystem and hydrologic processes. Analysis of spatiotemporal variations and influencing factors ofET in the growing season is of great importance to evaluate the growing environment for crops andto effectively use water resources across the Songnen Plain, a critical base for grain production inChina. The authors made use of the Surface Energy Balance Algorithm for Land (SEBAL) and thePenman-Monteith equation (P-M) in conjunction with Moderate-resolution ImagingSpectroradiometer (MODIS) products (i.e., MOD11A1, MOD11A2, MOD13A2, MOD43B3, andMCD43B3) to estimate land surface actual ET in the growing season generally from May toSeptember during the period 2000-2008. Furthermore, spatial patterns and temporal trends in theET estimates were comprehensively analyzed, with investigating correlation of five key climaticfactors (i.e., precipitation, air temperature, relative humidity, wind speed, and sunshine hours) withET estimates. In addition to large water bodies and wetlands, the average ET in the growing seasonfrom 2000 to 2008 changed obviously, increasing gradually from the southwest to the east andnortheast of the study region. It was suggested that the average ET of the whole Songnen Plainexhibited a significant decreasing trend during the period 2000-2008, with a maximum ET value of669.31 mm occurring in 2000 and a minimum ET value of 570.79 mm in 2005. The mean annualET was found to be roughly 612.63 mm. Under a combined effect of weather conditions, soil watersupply status, and fractional vegetation cover, the monthly ET from May to September showed amarked spatiotemporal variation, with a maximum monthly ET value of 141.60 mm in July and aminimum ET value of 81.35 mm in September. This could be ascribed largely to relatively lessprecipitation and lower air temperatures. By examining responses of the ET estimates to climaticvariables, it was found that ET was positively correlated with precipitation and average airtemperature over most regions of the Songnen Plain, indicating that the two climatic variables maybe the major factors affecting ET for the growing season. Additionally, average relative humiditywas positively correlated with ET in areas covered primarily by forests and water bodies, whereasshowed negative correspondence with ET over other regions. The ET estimates showedinsignificant correlation with climatic factors, such as wind speed and sunshine hours. This workwould provide a basis for the assessment of water supply status during the crop growth stage overthe Songnen Plain, particularly over the arid and semi-arid environments. It can also facilitateassessing ecological water requirement and irrigation system functions, further strengthening waterresources management.