Data from: Exacerbated grassland degradation and desertification in Central Asia during 2000-2014

Grassland degradation and desertification is a complex process, including
both state conversion (e.g., grasslands to deserts) and gradual
within-state change (e.g., greenness dynamics). Existing studies hardly
separated the two components and analyzed it as a whole based on time
series vegetation index data, which however cannot provide a clear and
comprehensive picture for grassland degradation and desertification. Here
we proposed an integrated assessment strategy, by considering both state
conversion and within-state change of grasslands, to investigate grassland
degradation and desertification process in Central Asia. First, annual
maps of grasslands and sparsely vegetated land were generated to track the
state conversions between them. The results showed increasing grasslands
were converted to sparsely vegetated lands from 2000 to 2014, with
desertification region concentrating in the latitude range of 43-48°N. A
frequency analysis of grassland versus sparsely vegetated land
classification in last 15 years allowed a recognition of persistent desert
zone (PDZ), persistent grassland zone (PGZ), and transitional zone (TZ).
The TZ was identified in southern Kazakhstan as one hotspot which was
vulnerable and unstable for desertification. Furthermore, the trend
analysis of Enhanced Vegetation Index during thermal growing season
(EVITGS) was investigated in individual zones using Linear Regression and
Mann-Kendall approaches. An overall degradation across the area was found;
moreover, the second desertification hotspot was identified in the
northern Kazakhstan with significant decreasing in EVITGS, which was
located in PGZ. Finally, attribution analyses of grassland degradation and
desertification were conducted by considering precipitation, temperature,
and three different drought indices. We found persistent droughts were the
main factor for grassland degradation and desertification in Central Asia.
Considering both state conversion and gradual within-state change
processes, this study provided reference information for identification of
desertification hotspots to support further grassland degradation and
desertification treatment, and the method could be useful to be extended
to other regions.