近30 a拉萨河流域土地利用变化和生境质量的时空演变特征

Spatial-temporal evolution characteristics of land use change and habitat quality in the Lhasa River Basin over the past three decades

为明晰高原流域土地利用变化时空特征及其对生境质量的影响,以典型高原流域——拉萨河流域为例,基于GEE平台和随机森林分类算法,解译拉萨河流域1990—2020年土地利用信息,分析30 a间土地利用的时空动态变化特征,并结合InVEST模型评估流域生境质量,探讨流域生境质量变化特征。研究结果表明:针对高寒高海拔地区的土地利用分类问题,筛选植被生长季,用相邻年份的影像进行补充和替换缺失的数据,并去云后生成的年度合成影像,提高了地类分类效率和精度;建立了一种结合Landsat影像光谱特征、纹理特征和地形特征的最优RF分类模型,实现了对高原流域土地利用信息的提取,OA、Kappa系数和F1-score分别在88.16%、0.84和0.70以上;20世纪90年代以来,拉萨河流域土地利用变化特征整体表现为“五增三减”,草地、建设用地、林地、湿地和水域面积增加,耕地、冰川及永久积雪和未利用地面积减少,其中,建设用地的增长幅度最大,达到288.35%,而耕地缩减最多,达50.18%,且耕地减少主要是受到城镇范围扩张的挤占;未利用地面积减少最为显著,其转出部分主要转化为草地;研究期内高质量生境主要分布在流域下游、西南侧以及源头区域,以草地、水体、冰川及永久积雪和湿地等土地利用类型为主;而拉萨市市辖区、达孜区、林周县、曲水县和墨竹工卡县县城周边,以及流域中上游的未利用地等区域生境质量较差;流域整体生境质量呈“先减后增再减然后趋缓”的变化趋势,生境质量指数从0.53提升到0.57;人口增加和快速城镇化加快了城镇范围扩张和耕地的减少,但气候变化和生态治理工程对拉萨河流域的生境质量改善均起到了积极作用;本研究可为制定高原地区流域生态修复策略、促进土地利用可持续以及提升生境质量提供科学依据与参考。

This study used the Lhasa River Basin,which is a typical plateau basin to clarify the spatiotemporal characteristics of land use change and its impact on a plateau basin habitat quality.The google earth engine(GEE) platform and random forest classification algorithm were used to interpret the land use information of the Lhasa River Basin from 1990 to 2020,and to analyze the spatiotemporal dynamic changes of land use in the past30 years.The InVEST model was integrated to evaluate the habitat quality of the basin,and to explore the characteristics of its habitat quality changes.The results showed that the efficiency and accuracy of land use classification improved by selecting the vegetation growing season,supplementing and replacing missing data with images obtained in the previous and following years,and generating annual composite cloud free images for land use classification in the alpine and high-altitude areas.An optimal RF classification model combining the spectral,textural,and topographical features of Landsat images was established to classify land use information in the plateau basin.The observed OA,Kappa coefficient,and the F1-score were 88.16%,0.84,and 0.70,respectively.Since the 1990,the features of the land use change in the Lhasa River Basin have been characterized by “five increases and three decreases,” with an increase being observed in the areas under grassland,construction,forest land,wetland,and water,while the areas under cultivated land,glaciers,and permanent snow or unused land having a decrease.Among them,the growth rate of construction land had the largest increase of 288.35%,while the largest decrease was detected in cultivated land with 50.18%,which could mainly be attributed to overpopulation in the urban areas.Most significant decrease occurred in the unused land area,and the changed area was mainly converted with grassland.During the study period,high quality habitats were mainly distributed in the downstream areas,southwest,and the main source areas of the basin,included the grassland,water,glaciers,permanent snow,and wetland.Poor qualities of habitats were observed in the Lhasa municipal district,Dazi District,Linzhou County,Qushui County,and Mozhugongka County,as well as in the unutilized land in the middle and upper reaches of the basin.The overall habitat quality of the watershed showed an alternating transition pattern of initial decrease,then increase,followed by a decrease,and a slowed down transition,while the habitat quality index increased from 0.53 to 0.57.Population growth and rapid urbanization accelerated the expansion of urban areas and the reduction of arable land,while climate change and ecological engineering played a positive role in improving the quality of habitat in Lhasa River Basin.This study provides a scientific basis and reference for formulating ecological restoration strategies,sustainable land use,and habitat quality improvement in a plateau area.