1990—2021年西藏“一江两河”流域湿地时空变化分析研究

Analysis on Spatial and Temporal Changes of Wetlands of Yarlung Zangbo River and Its Two Tributaries in Tibet from 1990 to 2021

为了研究30年来西藏“一江两河”流域湿地时空变化,采用1990—2021年Landsat TM影像作为数据来源,应用随机森林和支持向量计算法提取西藏“一江两河”流域各年份的湿地数据,分析西藏“一江两河”流域湿地时空分布、面积变化和形状变化等特征。研究结果表明:湿地的时空变化受到人类活动与自然因素的双重制约,高原湿地尤其容易受到人类活动扰动,随着人类区域经济开发活动强度的不断加深,高原湿地发生了较大的变化;湿地形态变化明显,河流所占的比例减少,湖泊和滩涂比例上升,沼泽所占比例下降最为明显;湿地面积在近30年里呈现出波动上升,前20年湿地面积变化不明显,之后11年湿地呈现急剧增加状态。研究区湿地的空间变化以稳定型和增加型为主,其主要分布于流域河谷周边,这里人类活动相对较少,且东部地区大于中西部地区;减少型主要分布于“一江两河”流域的河谷区域,这里往往是人类活动的中心区域,表明湿地总面积虽然不断增加,但是人类活动对局域湿地扰动依然存在。

In order to study the spatial and temporal changes of wetlands in the Yarlung Zangbo River and its two tributaries in Tibet in the past 30 years,based on data extracted from Landsat TM images between 1990 and 2021 with random forest and support vector machine,the temporal and spatial changes in wetlands of Yarlung Zangbo River and its two tributaries in Tibet were analyzed from these three aspects:temporal and spatial distribution,area changes and shape changes.The results showed that the temporal and spatial changes of wetland were restricted by human activities and natural factors,and the plateau wetland was especially vulnerable to human disturbance.With the deepening of the intensity of human regional economic development activities,the plateau wetland had also undergone great changes.The inter-annual fluctuation of precipitation was significant,leading to the increase trend of fluctuation in wetlands.However,the wetland morphology changed obviously,with its proportion of rivers decreasing,proportion of lakes and tidal flats increasing,and proportion of marshes decreasing most obviously.In the past 30 years,the wetland area fluctuated.In the first 20 years,the wetland area did not change significantly,while in the next 11 years,it increased sharply.The spatial changes of wetlands in the study area were mainly stable and increasing,which mainly distributed around the valley basin,and where human activities were relatively less,and the eastern region was larger than the central and western regions,and the decreasing type was mainly distributed in the valley area of Yarlung Zangbo River and its two tributaries in Tibet valley basins,which was often the center area of human activities,indicating that although the total area of wetlands increased,the local disturbance of wetlands was still affected by human activities.