土地利用/覆被变化扎龙湿地蒸散发量及生态需水量的遥感估算

Abstract

地表蒸散发量是影响湿地水热平衡的主要因素，也是水分损失的主要途径，对湿地生态需水量的合理确定和水资源的有效管理具有重要意义。借助遥感和GIS技术，利用2002、2010、2016年34景Landsat影像，基于时序NDVI数据对湿地下垫面物候特征的定量表征，准确获取了扎龙湿地保护区3个时期土地利用/覆被的动态变化信息。选用物理基础较好且应用广泛的SEBAL模型，估算了湿地的瞬时蒸散发量，并结合站点气象数据，实现了湿地蒸散发量在时间尺度上的扩展，分别得到日、月、年尺度的湿地蒸散发量，深入探究了扎龙湿地蒸散发的时空分布特征；最后从湿地湖泡需水量、植物需水量及生物栖息地需水量3个方面，定量估算出扎龙湿地3个时期的现状生态需水量。研究发现：扎龙湿地的土地覆被类型主要以芦苇沼泽、草地和耕地为主，其中芦苇沼泽分布占绝对优势，且2002-2016年持续增加了205.82 km²；草地、耕地呈持续减少态势，分别减少了119.35 km²和95.96km²，表明2002-2016年扎龙湿地生态系统呈恢复态势；湿地保护区蒸散发量年内均大致呈单峰型分布，符合夏季 > 春季 > 秋季 > 冬季的规律，在年际上呈现明显的递增趋势，年蒸散发量由2002年的518.87mm增加到2016年的625.98mm，增加了20.64%。为满足湿地内的生态消耗，总体上2002-2016年湿地的生态需水量也相应的增加，保护区适宜生态需水量的变动范围为5.40亿-7.08亿m³，可以维持湿地湖泊、植被、动植物栖息地的健康态势。维持核心区健康状态的最小生态需水量变化范围为2.71亿-3.32亿m³。随着遥感数据时空分辨率的提高，基于蒸散发量反演的湿地生态需水量估算将更加实用和准确，为湿地保护区制定科学合理的补水方案提供有效的技术支撑。;Surface evapotranspiration is a main factor influencing wetland water-heat balance and a main way of water loss. It has important significance for the reasonable determination of ecological water demand in wetlands and the effective management of water resources. With the help of remote sensing and GIS technology, the quantitative characterization of the phenological characteristics of the underlying surface of Zhalong wetland based on temporal NDVI data was made by using Landsat images of 34 scenes in 2002, 2010 and 2016. At the same time, the dynamic change information of land use/cover in three periods of the wetland reserve was obtained accurately. The SEBAL model with good physical foundation and wide application was selected to estimate the instantaneous evapotranspiration of the wetland. By combining with the meteorological data of nearby hydrographic stations, the temporal expansion of evapotranspiration of the wetland was realized. The daily, monthly and annual evapotranspiration of Zhalong wetland was obtained, and the spatio-temporal distribution characteristics of evapotranspiration in Zhalong wetland were deeply investigated. At last, the present ecological water demand of Zhalong wetland in three periods was quantitatively estimated from three aspects:water demand of wetland lake bubble, water demand of plants, and water demand of biological habitat. The results indicated that the land cover types of Zhalong wetland were mainly reed marshes, grasslands and cultivated land, among which reed marshes occupied the absolute dominance, increased by 205.82 km² continuously from 2002 to 2016. Grassland and cultivated land decreased by 119.35 km² and 95.96 km², respectively, indicating that Zhalong wetland ecosystem showed a recovery trend from 2002 to 2016. The annual evapotranspiration of the wetland reserve presented a roughly single-peak distribution in the three years, which was consistent with the summer > spring > autumn > winter. The annual evapotranspiration increased significantly from 518.87 mm in 2002 to 625.98 mm in 2016, by an increase of 20.64%. In order to meet the ecological consumption in the wetland, the total ecological water demand of the wetland increased correspondingly from 2002 to 2016. The range of the appropriate ecological water demand of the wetland reserve was 540 million m³ -708 million m³, which could maintain the health of the lakes, vegetation, animal and plant habitats in the wetland. The minimum ecological water demand for maintaining the health of the core area varied from 271 million m³ to 332 million m³. With the improvement of spatial and temporal resolution of remote sensing data, the estimation of wetland ecological water demand based on evapotranspiration inversion will be more practical and accurate, providing effectively technical support for the formulation of scientific and reasonable water rehydration schemes in wetland reserves.