NDVI‐indicated long‐term vegetation dynamics in Mongolia and their response to climate change at biome scale

Abstract

Based on the vegetation map of Mongolia, Global Inventory Monitoring and Modelling Studies (GIMMS) normalized difference vegetation index (NDVI) (1982–2006), the Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI (2000–2010), and temperature and precipitation data derived from 60 meteorological stations, this study has thoroughly examined vegetation dynamics in Mongolia and their responses to regional climate change at biome scale. To ensure continuity and consistency between the two NDVI datasets, the MODIS NDVI was first calibrated to the GIMMS NDVI based on the overlapping period of 2000–2006. Good calibration results with R2 values of 0.86–0.98 between the two NDVI datasets were obtained and can detect subtle trends in the long‐term vegetation dynamics of Mongolia. The results indicated that for various biomes, although NDVI changes during 1982–2010 showed great variation, vegetation greening for all biomes in Mongolia seem to have stalled or even decreased since 1991–1994, particularly for meadow steppe (0.0015 year−1), typical steppe (−0.0010 year−1), and desert steppe (−0.0008 year−1), which is an apparent turning point (TP) of the vegetation growth trend in Mongolia. A pronounced drying trend (from −4.399 mm year−1 in meadow steppe since 1990 to −2.445 mm year−1 in alpine steppe since 1993) occurred between 1990 and 1994, and persistently warming temperatures (0.015 °C year−1 in alpine steppe to 0.070 °C year−1 in forest and meadow steppe) until recently have likely played a major role in this NDVI trend reversal. However, the NDVI TP varied by biome, month, and climate and was not coupled exactly with climatic variables. The impact on climate of both same‐time and lagged‐time temperature and precipitation effects also varied strongly across biomes and months. On the whole, climate‐related vegetation decline and associated potential desertification trends will likely be among the major sources of ecological pressure for each biome in Mongolia, which could intensify environmental problems like sandstorms in other East Asian regions.

Response of seasonal soil freeze depth to climate change across China

“…A significant climate indicator, SFD is influenced by many variables including climatic and environmental factors. These factors are often integrated to affect SFD (Lachenbruch and Marshall, 1986;Brown et al, 2000;Frauenfeld et al, 2004). Our results can be summarized as follows.…”

“…The increasing thickness of the active layer has been indicated by many observations in permafrost regions at high latitudes and altitudes (Brown et al, 2000;Frauenfeld et al, 2004;Zhang et al, 2005;Fyodorov-Davydov et al, 2008;Wu et al, 2010;Zhao et al, 2010;Callaghan et al, 2011;Liu et al, 2014a, b;Stocker et al, 2014). Less research has focused on SFG areas Frauenfeld et al, 2004;Frauenfeld and Zhang, 2011;Wang et al, 2015), although the near-surface soil freezethaw status has been investigated using satellite passive microwave remote sensing (Zhang and Armstrong, 2001;Zhang et al, 2003Zhang et al, , 2004Li et al, 2008;Jin et al, 2015).…”

“…Because climate change controls the spatial distribution of vegetation, most studies report vegetation increases as impacted by temperature and precipitation increases (Bao et al, 2015;Huang et al, 2016). Similarly, Fig.…”

Ecohydrological optimality in the Northeast China Transect

“…Previous studies suggest there are lagged relationships between NDVI and climate factors, and the time lags are different in different regions or different biomes (Braswell et al, 1997;Piao et al, 2003;Li et al, 2011;Hu et al, 2011;Bao et al, 2015). Figure 4 shows that, in the grassland area, the variation amplitude of M is smaller than M * , and the delay usually happens within a year, while in the forest area, there is a trend delay across the years.…”

Ecohydrological Optimality in Northeast China Transect

“…Previous researches suggest there are lagged relationship between NDVI and climate factors, and the time lags are different at different region scales or different biomes (Braswell et al, 1997;Piao et al, 2003;Li 15 et al, 2011;Hu et al, 2011;Bao et al, 2015). Fig.…”