Assessment of changes in the normalized difference vegetation index (NDVI) of farmlands of Stavropol Territory, Russia, during the period of active vegetation in 2020 based on medium spatial resolution images

Aim. Assess changes in the NDVI of agricultural land in Stavropol Territory under the influence of weather and climate conditions.

Methods. Based on earth remote sensing data, the spectral/vegetation index NDVI was calculated. We used data from the Meteor‐M satellite with a spatial resolution of 60 m for the active vegetation period of 2020 (May to September), which made it possible to calculate the NDVI value at different times of the active vegetation period of the main types of agricultural land in the Stavropol Territory. To explain the spatial and temporal variability of NDVI, an analysis of the conditions of heat and moisture supply was carried out using Walter's climatograms at weather stations located in the steppe and semi‐desert landscapes of Stavropol Territory.

Results. In 2020, the period of active vegetation in the steppe and semidesert landscapes of Stavropol Territory began in the first ten days of April, when the air temperature rose above +10°С, and ended in mid‐October. In accordance with the change in heat and moisture supply, the NDVI value changed: in general, maximum values were observed in spring and early summer and, as aridity increased, the areas corresponding to low NDVI values increased everywhere. In the steppe zone, where the main crops of winter wheat are located, the NDVI value decreased from 0.45–0.3 at the beginning of the active vegetation period to 0.15 at the end. NDVI values of 0.15–0.30, corresponding to different types of herbaceous vegetation, prevailed at the end of the active vegetation period.

Conclusion. The spatial and temporal distribution of the NDVI value over the territory of the Stavropol Territory reflects, first of all, changes in the conditions of heat and moisture supply. The timing of the course of the phenological phases of natural and cultivated vegetation depends on the latter. 2020 was characterized by sufficient moisture at the beginning of active vegetation, as reflected in the high density of seedlings, and, accordingly, a large area of NDVI, corresponding not only to herbaceous, but also to shrubby vegetation within the steppe landscapes. The increase in moisture deficit and harvesting in the second half and end of summer leveled the differences between the steppe and semi‐desert landscapes, since the maximum areas were occupied by territories with NDVI values of 0.15–0.3.

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