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Monitoring of Vegetation Dynamics in the Mongolia Using MODIS NDVIs and their Relationship to Rainfall by Natural Zone

Vegetation plays a very important role conserving
the natural environment and improving the living environment
for humans. Thus, investigating spatio-temporal changes
in vegetation is a crucial indicator to understand natural environmental
changes. We explored the spatio-temporal trends of
changing vegetation cover in Mongolia from 2002 to 2010 by
investigating changes in the normalized difference vegetation
index (NDVI) with rainfall. The 16-day composite NDVI time
series Terra MODIS (MOD13A2) and the gridded rainfall
data of the Inter-governmental Panel on Climate Change
(IPCC) were used to identify the relationship between vegetation
dynamics and rainfall. Residual NDVI trends were
computed. Following our general procedure, monthly NDVI
and annual rainfall were correlated for each pixel. The
resulting regression equation represented the statistical association
between observed NDVI and rainfall, and the model
predicted NDVI according to rainfall. Residuals of NDVI
(differences between the observed and predicted NDVI) for
each pixel were calculated, and the trends in these residuals
was analyzed by linear regression. From the 12 months NDVI
and rainfall values they determine a linear regression line for
each pixel. The positive or negative slope of this line is
considered to reflect an increase or decrease in green biomass.
Our results show that vegetation cover changes in Mongolia
were caused by both natural factors and human activities. The
natural vegetation change, such as those in forests was influenced
by climate change, whereas human activities were the
main reason for the change in vegetation planted.