Abstract
The vegetation response to climatic factors is a hot topic in global change research. However, research on vegetation in Shule River Basin, which is a typical arid region in northwest China, is still limited, especially at micro scale. On the basis of Moderate-resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) data and daily meteorological data, employing panel data models and other mathematical models, the aim of this paper is to reveal the interactive relationship between vegetation variation and climatic factors in Shule River Basin. Results show that there is a widespread greening trend in the whole basin during 2000–2015, and 80.28% of greening areas (areas with vegetation improvement) are distributed over upstream region, but the maximum vegetation variation appears in downstream area. The effects of climate change on NDVI lag about half to one month. The parameters estimated using panel data models indicate that precipitation and accumulated temperature have positive contribution to NDVI. With every 1-mm increase in rainfall, NDVI increases by around 0.223‰ in upstream area and 0.6‰ in downstream area. With every 1-°C increase in accumulated temperature, NDVI increases by around 0.241‰ in upstream area and 0.174‰ in downstream area. Responses of NDVI to climatic factors are more sensitive when these factors are limiting than when they are not limiting. NDVI variation has performance in two seasonal and inter-annual directions, and the range of seasonal change is far more than that of inter-annual change. The inverted U-shaped curve of the variable intercepts reflects the seasonal change. Our results might provide some scientific basis for the comprehensive basin management.
Highlights
Vegetation, the main component of the terrestrial biosphere, is a crucial element in the climate system [1]
Using the vegetation information obtained from Landsat Thematic Mapper (TM) images, which has a high spatial resolution of 30 m, we considered MAXNDVI5–10 ≥ 0.12 is an appropriate threshold value that denotes vegetation in Shule River Basin
Linear Trend Analysis Change in Normalized Difference Vegetation Index (NDVI) over time could be expressed as the following regression equation [47]: yi = θi + b i = 1, 2, 3, · · ·, n where yi is the NDVI value in ith year, b is the intercept, n is the number of years in the study period, and θ is the slope representing linear trend of NDVI change, which is estimated by the least square method
Summary
Vegetation, the main component of the terrestrial biosphere, is a crucial element in the climate system [1]. Understanding the relationship between the greenness of vegetation and climate is an important topic in global change research [3]. The vegetation in the arid regions in west China, which is a sensitive and fragile ecological zone, has a sensitive response to the global climate change. This region becomes one of the key areas for studying global environmental changes [4]. NDVI can be used to represent the proxy vegetation responses to climate changes since it is well correlated with the fraction of photosynthetically active radiation absorbed by plant canopies and leaf area, leaf biomass and potential photosynthesis [6]
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