植被恢复影响下黄河上游北川河流域蒸散发量变化及成因分析

针对黄河上游水源涵养区植被恢复的水循环影响问题，结合北川河流域的植被覆盖和蒸散发遥感数据以及土壤蒸发野外观测数据，分析植被恢复影响下蒸散发这一关键水循环要素的变化趋势及成因，阐明高寒山区植被恢复对流域蒸散发量变化的潜在影响途径。结果表明：2000-2019年，随着北川河流域植被覆盖度的持续增加，流域年蒸散发量减少了33.23 mm,其中，7、8月份植被主要生长季内蒸散发量减少最为明显，对年蒸散发量的降低具有决定作用；2019年6-9月期间，典型植被恢复区林下土壤蒸发量为207.38 mm,比林外土壤蒸发量减少了157.73 mm,林下土壤蒸发量减少是引起流域蒸散发量减少的一个重要因素，植被作用于地表风速、辐射强度等气象因子而引起的变化对减小流域潜在蒸散发强度具有促进作用。高寒山区蒸散发量随植被恢复而减少的变化趋势与黄土高原及东部地区存在一定差异，这与其寒冷的气候特征及以针叶林为主的植被类型具有一定关系，体现了黄河上游生态涵养林建设的水源涵养功能。

Changes of evapotranspiration and the causes in the Beichuan River Basin of the upper Yellow River under the influence of vegetation restoration

Targeting the effect of vegetation restoration on the water cycle in the upstream of Yellow River, based on the vegetation coverage, remote sensing and field observation data of the evapotranspiration in the the Beichuan River Basin, the evolution trend of evapotranspiration and the causes of its changes were analyzed to investigate the potential influencing path of the vegetation restoration in alpine mountainous area on the changes of evapotranspiration on the basin scale. The results show that the evapotranspiration decreased by 33.23 mm in Beichuan River Basin from 2000 to 2019 due to the continuous increase of the vegetation coverage. The reduction of evapotranspiration in July and August, which is the main vegetation growth season, dominated the annual reduction. During the period of June to September, 2019, the soil evapotranspiration in the forest was 207.38 mm, which was 157.53 mm lower than that outside the forest, this was also conducive to the decrease of evapotranspiration in the basin. Meteorological factors such as surface wind speed, which were greatly influenced by vegetation, played an important role in the reduction of the potential evapotranspiration strength in the basin. The variation trend of evapotranspiration in alpine mountainous area in the background of vegetation restoration was different from that in the Loess Plateau and the eastern region, which was associated with its cold climate characteristics and the dominant vegetation type (coniferous forest). Furthermore, it fully reflected the water conservation function of ecological conservation forest in the upstream of the Yellow River.