Ephemera and ephemeroid plants form a short-term but relatively developed herbaceous cover during spring in South Kazakhstan. This important component of vegetation of arid territories develops in early spring due to moisture accumulated during the cold period. Satellite monitoring of vegetation states allows assessing the reaction of ephemera and ephemeroids to long-term weather variations. In this research, the direction of monotonous NDVI (Normalized Difference Vegetation Index) trends is estimated for the territory of South Kazakhstan. The MOD13Q1A1(NDVI) 500-m resolution data for 2000–2022 and the nonparametric Mann–Kendall (M-K) test are used. The South Kazakhstan growing season from March to October is described by 15 separate 16-day time windows of the MOD13Q1 product. The M-K test is used to determine whether a time series has a monotonic upward or downward trend. The M-K test values, in the format of the difference between the number of concordant and disconcordant pairs of samples, are used. By threshold values of +3.5 and –3.5, the time series are ranked to three types of monotonous trends: ascending (>+3.5), descending (<–3.5), and uncertain. The received values are grouped into seasonal (spring, summer, autumn) sets. Each set includes five 16-day assessments: spring from March 5 to May 23, summer from May 24 to August 11, and autumn from August 12 to October 30. The end result for each 500 × 500-m elementary section is an average assessment of the trend direction of the 16-day MOD13Q1A1(NDVI) values during the 80‑day period of the analyzed time of year (spring, summer, autumn). The obtained values of the average trend direction range from –100 to +100%, which corresponds to either five downward or five upward trends. Previously, a test site has been allocated in South Kazakhstan, with an area of about 50 thousand km2, which, according to NDVI (160 scenes from Sentinel‑2 of March–October 2018–2022), was dominated by vegetation of the spring period. It is found that the spring vegetation of the period from March 5 to May 23, attributed by the terms of vegetation to the development of ephemera and ephemeroid plants, has an average assessment of monotonous trends for the analyzed contour equal to –21.95%; for summer vegetation, –48.63%; and for autumn vegetation, –53.13%. Thus, in South Kazakhstan, during 2000–2022, a dominance of negative trends in the vegetation state in the zone of prevailing ephemera and ephemeroid plants is recorded. At the same time, the trends in spring vegetation appear somewhat better than the trends in summer and autumn vegetation with more pronounced downward slide.
Terekhov et al. (2025) studied this question.