基于MODIS和CLCD数据的黄土高原土地利用变化检测及其对植被碳吸收模拟的影响

Land-Use and Land-Cover Change(LUCC)Detection Based on MODIS and CLCD Data and Its Impact on the Simulation of Vegetation Gross Carbon Assimilation in the Loess Plateau

该文选取MODIS LULC产品(MCD12Q1)和精度较高的CLCD LULC产品分析2001—2019年黄土高原LUCC的时空变化格局,并进一步利用陆面生态过程模型(FGM)模拟分析黄土高原陆地生态系统总初级生产力(GPP)变化以及MCD12Q1时序产品分类误差对GPP模拟结果的影响。结果表明:MCD12Q1数据错误显示2001—2019年黄土高原地区呈“耕地增加、草地减少”的LUCC格局,主要由MCD12Q1数据对耕地和草地分类混淆导致,而CLCD LULC数据则正确捕捉到黄土高原地区“耕地减少、草地和林地增加”的LUCC变化规律;基于CLCD LULC产品驱动的FGM模拟结果显示,黄土高原陆地生态系统GPP年总量约为5210.2 Tg C a^(-1),退耕还林还草实施20年来其植被碳吸收能力显著增强(变化趋势为6.4 Tg C a^(-2),P<0.001);若采用长时序MCD12Q1数据驱动FGM模型,会造成GPP年总量高估约9.6%、GPP年际变化趋势高估22.7%。研究结果对于科学认识黄土高原陆地生态系统植被的结构和功能变化、国家重大生态工程策略制定和可持续发展具有参考意义。

Significant land-use and land-cover change(LUCC)has occurred in the Loess Plateau in recent 20 years,which has made an important contribution to the carbon sink of the terrestrial ecosystem.The accuracy of the representation of the temporal variation in LUCC is one of the most important factors affecting the accuracy of estimation of carbon exchange between terrestrial ecosystem and atmosphere.In this paper,the MODIS LULC product(i.e.,MCD12Q1)and the CLCD LULC product with relatively high accuracy were introduced for comparative study.Firstly,the temporal and spatial change pattern of LUCC in the Loess Plateau from 2001 to 2019 was analyzed based on MCD12Q1 and CLCD LULC products.Then,the spatial and temporal variations in GPP in the Loess Plateau from 2001 to 2019 were simulated by a process-based terrestrial biosphere model named Farquhar GPP model(FGM).Finally,the impact of classification errors of the MCD12Q1 time series data on GPP estimation was analyzed quantitatively.The results indicated that MCD12Q1 data incorrectly displayed a LUCC pattern of"increase of arable land and decrease of grassland"in the Loess Plateau region from 2001 to 2019.This could possibly be explained by the confusion in classifying arable land and grassland in MCD12Q1 data.In contrast,time-series CLCD LULC data correctly captured the LUCC variation pattern of"decrease of arable land,increase of grassland,and increase of forest land"in the Loess Plateau.The FGM simulation results based on CLCD LULC data showed that the annual total GPP of the terrestrial ecosystem in the Loess Plateau was about 5210.2 Tg·C·a^(-1).From 2001 to 2019,the annual total GPP of the Loess Plateau has increased significantly(6.4 Tg·C·a^(-2),P<0.001)under the implementation of the Grain for Green Project.If the MCD12Q1 time-series data from 2001 to 2019 is used to drive the FGM model,it will cause an overestimation of approximately 9.6%of the annual total GPP and an overestimation of nearly 22.7%of the interannual variation trend of GPP.The research results are of great significance for scientific understanding of the changes in the structure and function of vegetation in the terrestrial ecosystem of the Loess Plateau,formulation of strategies for major national ecological engineering and sustainable development.