THE ANALYSIS OF SATELLITE MEASUREMENT OF THE VEGETATION INDEX IN THE FOOTHILL AND PLAIN AREAS OF THE RSO-ALANIA

Abstract

To analyze the seasonal and long-term variability of the normalized relative vegetation index NDVI, the multichannel MODIS spectroradiometer measurements with a 10x10 km resolution over a 20-year period of time are used. On the territory of the RNO-Alania in the foothill areas and on the plains near the border of the Stavropol Territory five geographical locations are selected, located at different distances from the Northern spurs of the Caucasian Ridge. For each geographical location the sets of time series are obtained for: 16-day NDVI composites, daily temperature at an altitude of 2 m and precipitation for the 20-years period from 01.01.2000 to 31.12.2019. By calculating the integral characteristic for an annual period of time for every location, the series of 20 annual values are obtained. According to the obtained series, three 20-year trends are built and the trend parameters of a first-order polynomial are calculated using the least squares method. The NDVI trend slope switch is observed in the Mozdok-Russkoe location for transition from the time period 2000–2009 to the period 2010–2019, when the slope changes from positive to negative. Similar NDVI trend slope switches are observed for other locations. This may be due changing the level of soil moisture over time, taking into account mainly the downward trends in precipitation. The trend slope of the NDVI integral characteristic 5–15 % increases with the increasing of the distance from the mountain ridge. The temperature trends for all locations are ascending, that indicates an average increase of the number of warm days from year to year. At the same time, the maximum temperature during the summer period does not significantly increase. The trend of the integral characteristic for the amount of precipitation is mainly downward. However, its specific values have a fairly large spread, which means that the amount of precipitation varies significantly from year to year. In addition, the amount of precipitation decreases with distance from mountain ridges. These factors should be taken into account when choosing agricultural products for cultivation and planning additional land-reclamations in the flat and foothill areas on the south of the Russian Federation.