Spatial And Temporal Variations Of Vegetation Phenology In China

There is no doubt that global warming has happened since 20th century. And climate change has had a significant influence on vegetation phenology. It is helpful to indicate the response of biosphere to seasonal and interannual variations of climate, hydrology, soil and anthropogenic factor by vegetation phenology. Grasping its phenological variation in crop yield estimation, and forecasting farming season, monitoring, protecting the ecological environment, and prediction of climate change trends have important theoretical and practical significance, which has important meaning in the study of global climate change and ecosystem as well.Lots of methods are used to produce vegetation phenology product and analyses its spatial and temporal variations using time-series MODIS EVI data in the paper. The research achievements in this paper are concluded as follows:1. Wavelet transform is applied to time series of MODIS EVI data in order of generate intra-annual vegetation pattern for exploring vegetation changes during 2001-2012. We get a better curve is called V-curve which is more fit to study vegetation phenology based on discrete wavelet. For this work, natural vegetation phenology and crop phenology are characterized by 5 and 6 key transition dates respectively. First, cycle number is determined. Then all key transition dates should be extracted in each vegetation life cycle. Vegetation phenology is included cycle number, start of green, fast start of green (only in crop lands), heading date, end of green and length of growing season. The key transition dates are not all the same.2. Generally consistency between Remote-sensing phenology key transition dates and vegetation growing development, especially in crop lands. The results have high precision and reliability through 1097 validation samples. And heading date and end of green of vegetation phenology has higher accuracy than start of green.3. This work analyzed spatial and temporal variations of vegetation phenology in China. By and large, vegetation phenology has a very significant spatial character, but not the same in temporal variations (only 10% has a significant trend in study area). And only end of green of vegetation has a more significant trend in these places, delay an average 1 day in a year.4. Average temperature change presents a decreasing trend in many zones of China. This paper discussed the influence responding of vegetation phenology and temperature. Results indicated that average of temperature and vegetation phenology have significant correlation. A mathematical formula among the trend of environmental factors, correlation and the trend of vegetation phenology is proposed based on the study.