作 者 ：奚歌,刘绍民*,贾立
期 刊 ：生态学报 2008年 28卷 11期 页码：5356~5369
Keywords:Yellow River Delta wetland, evapotranspiration, ecological water requirement, remote sensing,
摘 要 ：蒸散量（ET）是黄河三角洲湿地水资源的主要消耗项，包括植被蒸腾、水面蒸发以及裸土蒸发等。植被生态需水是为了保证植被生态系统能够健康维持并确保其生态服务功能得到正常发挥而必须消耗的一部分水量。准确地估算湿地蒸散量、研究植被生态需水量对于保护湿地生态环境是十分必要的。应用MODIS的地表反射率、地表温度数据与常规气象数据以及土地利用/覆盖图，利用蒸散量的遥感估算模型SEBS模型估算了晴天条件下的黄河三角洲湿地日蒸散量，采用HANTS算法插补了非晴天条件下的日蒸散量，从而得到2001～2005年的该湿地年蒸散量的时间序列，并对蒸散量进行验证和分析。结合该地区典型植被生态需水量与植被蒸散耗水量，估算了2001~2005年的生态补水量。结果表明：与实测值相比，遥感估算月蒸散量的均方差RMSD为16.4mm，平均绝对百分比误差MAPD是11.9%，两者基本一致。黄河三角洲湿地的蒸散量在空间分布上以水体及周围地区、滨海滩涂、黄河故道以及黄河两岸沼泽湿地等的蒸散量较高，居民地蒸散量较低。蒸散量的年际变化不大，季节变化呈单峰型，以5、6、7月份蒸散量最大，月蒸散量在110~120mm之间。2001~2005年期间，每年至少有40%面积的芦苇沼泽和60%面积的芦苇草甸水分供应不足，植被的正常生长受到影响，尤其2002年较为严重，2004年以后情况有所改善。2002年芦苇的生态补水量最大，在9.9×107~3.19×108m3之间，而2004年的生态补水量最小，在3.0×107~2.39×108m3之间。
Abstract:Evapotranspiration (ET) from the wetland of the Yellow River Delta (YRD) is one of the important components in the water cycle, which represents the water consumption by vegetation and evaporation from land surfaces such as the water and bare soil. Water shortage reduces photosynthesis and, therefore, the growth rate of vegetation. Healthy and abundant vegetation is necessary to protect the wetland ecosystem. Reliable estimates of the total amount of water required and of actual water consumption by the wetland are necessary to protect the YRD wetlands. In this study, the SEBS (Surface Energy Balance System) model based on the Energy Balance method was used to calculate daily ET using conventional meteorological data and instantaneous observations of land surface reflectance and temperature from MODIS when the data were available on clouds-free days. A detailed vegetation classification map was used to identify different vegetation types to parameterize surface roughness. An algorithm based on the Fourier transform was then applied to generate a time series of daily ET over a year period by filling the gaps in the calculated daily ET time series due to clouds. Annual ET between 2001 and 2005 was calculated after filling the gaps in the daily ET for each yearly data set. The estimated daily ET was validated by comparing the ET over open water bodies with the pan evaporation observations at meteorological stations. The error of estimate of the monthly ET was 16.4mm or 11.9%, which is comparable with the accuracy of ground measurements. The ecological water demand by Phragmites australis including Phragmites australis-swamp and Phragmites australis-meadow which is the dominant wetland vegetation and the amount of water supply to maintain Phragmites australis in a good growth condition, were evaluated for the period between 2001 and 2005. The ET in the areas around water bodies, by the sea shores and the Yellow River former channel and in the swamps near the banks of Yellow River shows higher values, while the ET in residential areas is rather low. The yearly ET over different wetland vegetation types shows varying values ranging between 671 mm and 1017 mm. The interannual variation of the total ET is not very significant. The highest monthly ET is observed in May, June and July, ranging between 110mm and 120mm. Most of Phragmites australis wetland was affected by water shortages, with evident impacts on growth, from 2001 to 2005. The situation in 2002 was the worst due to less precipitation while it was improved after 2004 since higher precipitation was observed in 2004. The amount of the required water supply in 2002 was the highest between 0.099 billion m3 to 0.319 billion m3, while it was the lowest in 2004 between 0.03 billion m3 to 0.239 billion m3.
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