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Hiroshima University (2016)

Remote Sensing Based Monitoring for Land Degradation in Inner Mongolian Grassland

Gong Zhe

Titre : Remote Sensing Based Monitoring for Land Degradation in Inner Mongolian Grassland

Auteur : Gong Zhe

Université de soutenance : Hiroshima University

Grade : Doctoral Dissertation 2016

Résumé partiel
The Inner Mongolia grassland comprises more than 20% of China’s total grassland area, which made this region as the largest animal husbandry base in China. However, land degradation also occurred here, mainly due to the effects from human behaviors and climate change, threatening daily lives of the local residents. The main objective of this study is to evaluate the grassland degradation in Inner Mongolia on both quantity and quality levels using the remote sensing based methods. The dissertation has been divided into seven chapters. Chapter 1 clarifies the background and the objectives of the present study. Chapter 2, 3, and 4 study the grassland degradation dynamics on quantity level during different study periods. Chapter 5 applies nonlinear and non-stationary method for degradation trend analysis. Chapter 6 evaluates the grassland degradation on quality level. Chapter 7 makes general discussion of the whole dissertation. More detailed information are displayed below. In Chapter 2, a time series of NDVI data from 1983 to 2013, derived from the advanced very high-resolution radiometer Vegetation Health Product (AVHRR-VHP), was applied to detect linear trends, seasonal phenology transition dates, and growing seasons to assess the dynamics of the vegetation growth and phenology in the Inner Mongolia Autonomous Region in China. Overall, Inner Mongolia became warmer and drier during the study period. A significant increasing cumulative NDVI trend was found for 30.30% of the total vegetation covered area, and 21.21% of the area exhibited a significant decreasing trend. The degraded area was primarily located in the northeastern meadow and typical steppe regions. The restored area was mainly in the western desert steppe. The forest grew at a normal rate during these years. However, a severe drought during 1993–2003 was detected, when approximately 27.56% of the total vegetation covered area experienced a significant decreasing NDVI trend. The length of the growing season (LOS) in 1983–2013 shortened because of the delay of the start of the growing season (SOS) and the advance of the end of the growing season (EOS). However, this trend reversed in the more recent decade (2003–2013). The phenology was closely associated with climate change, especially precipitation. Moreover, the LOS was strongly correlated with the spring precipitation. The variability of the vegetation responses to climate change was also assessed, indicating that most of the vegetation types had recently recovered and that the restored areas had a varied spatial distribution.

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