The study of the features of NDVI trends of forest-tundra in Yakutia was carried out using GIMMS data (1982-2015). Trend maps of NDVI seasonal (May-September) values was constructed. Areas with the highest NDVI linear trend (10 – 15%) are located in the northern part of Yakutia. The highest NDVI seasonal trend is mainly due to significant increase (~26%) of May values during the past 12 years (2004-2015). Evaluation of the relationship between NDVI variations (May values) and meteorological parameters in the test site showed a high correlation (R=0.9) between NDVI and air temperature of May. The analysis of temperature changes (May values) showed also a significant increase of temperature trend (~6,1°С) during 2004-2015. While the relationship between NDVI and precipitation is negligible.
The study of NDVI variations and phenology dates of Eastern Siberia vegetation on NOAA satellite data (1982-2017) is carried out. Trend maps of seasonal NDVI (May-September) and maps of correlations NDVI with air temperature and precipitation were constructed. Area with the highest NDVI linear trend (10 – 15%) is located in the northern part of Yakutia. The increasing of NDVI seasonal trend is mainly due to significant increase of NDVI in May. Correlation between NDVI (in May) in the test site and air temperature is R=0.8. While the relationship between NDVI and precipitation is negligible. For 1982-2004 NDVI trend had near-zero values, but during 2004-2015 NDVI trend showed a significant increase about ~27%. The significant increase of air temperature (~30°C) during 2004-2015 is also observed in test site. Method “NDVI 0.3”1 based on NDVI threshold 0.3 was used to calculated the start and end of vegetation season in test site. In addition, BISE<sup>2</sup> algorithm was used to reducing noise in daily NDVI time-series. Analysis of phenology variations during 1982-2017 showed: the SOS shifted by ~12 days earlier and EOS by ~4 days later. Thus, the growing season has increased. The average trend of growing season length is ~16 days. For same time, the mean values NDVI of growing season increased by ~10% and mean values NDVI of July by ~17%.
Study of spatio-temporal variations of NDVI (Normalized Difference Vegetation Index) and phenological parameters of Eastern Siberia vegetation cover under global warming was carried out on AVHRR/NOAA data (1982-2014). Trend maps of NDVI and annual variations of phenological parameters and NDVI are analyzed. A method based on stable transition of air temperature through +5°C was used to estimate the beginning, end and the length of the growing season. Correlation between NDVI and phenological parameters, surface air temperature and precipitation are discussed.
Study of NDVI (Normalized Difference Vegetation Index) in Eastern Siberia was carried out on long-term (1982-2014) satellite data. 15-days average NDVI data (GIMMS project) was used to create the maps of NDVI trends distribution and correlation of NDVI with air temperature and precipitation. Using NDVI daily data (NOAA CDR Program data) over three test sites (in Yakutia), phenological parameters of tundra vegetation and deciduous needleleaf forests were calculated. It is shown, that for past three decades there is a positive NDVI trend in Eastern Siberia. Analysis of phenological parameters shows a tendency of an earlier SOS (start of season) and later EOS (end of season) for deciduous needleleaf forests and tundra vegetation. Air temperature is the major factor that defines positive trend of NDVI vegetation index under conditions of low precipitation.