Response of Vegetation Photosynthetic Activity to Net Radiation and Rainfall: A Case Study on the Tibetan Plateau by Means of Fourier Analysis of MODIS fAPAR Time Series
Received date: 2006-10-23
Revised date: 2006-10-23
Online published: 2006-12-15
Climate variability has a large impact on the vegetation dynamics. To quantify this impact in the Tibetan plateau a study was carried out using time-series of MODIS fAPAR satellite data products and NCEP net radiation and rainfall re-analysis data. The data set spanned over the years between 2000 and 2005. The NCEP data are used to construct a time series of a radiational indicator of drought: daily net radiation and rainfall data for each NCEP grid are integrated over a period of eight days to match the temporal sampling interval of MODIS data products. The ratio of net radiation over rainfall for a given period of time is a measure of excess energy relative to available water and is therefore a measure of drought hazard. Fourier analysis of time series of the MODIS fAPAR provides two indicators of the response of vegetation photosynthetic activity to drought, as measured by the indicator just described. The two indicators used in this study are the mean yearly fAPAR value and its annual amplitude. The algorithm used (HANTS) fits iteratively a Fourier series to a set of irregularly spaced observations, after elimination of outliers, such as due to cloud-contaminated observations. The relationships between photosynthetic activity of vegetation and the radiational drought hazard indicator are determined and quantified spatially and temporally. The response during the wettest respectively driest year during the period covered by available observations was compared. The drier areas prove to be the most sensitive to climate impact. The analysis should be extended over a longer period of time to obtain a more robust assessment of climate impact on vegetation dynamics, particularly as regards the response of vegetation to temporal respectively spatial variability of climate.
Key words： Phenology; Fourier.; Tibetan plateau; Drough; MODIS,fAPAR; Time series
JIA Li , M. Menenti, . Response of Vegetation Photosynthetic Activity to Net Radiation and Rainfall: A Case Study on the Tibetan Plateau by Means of Fourier Analysis of MODIS fAPAR Time Series[J]. Advances in Earth Science, 2006 , 21(12) : 1254 -1259 . DOI: 10.11867/j.issn.1001-8166.2006.12.1254
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