Data from: Exacerbated grassland degradation and desertification in Central Asia during 2000-2014
Zhang, Geli et al. (2017), Data from: Exacerbated grassland degradation and desertification in Central Asia during 2000-2014, Dryad, Dataset, https://doi.org/10.5061/dryad.12bd9
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.