Spatio-temporal Variations in Drought with Remote Sensing from the Mongolian Plateau During 1982–2018

The Mongolian Plateau is one of the regions most sensitive to climate change, the more obvious increase of temperature in 21st century here has been considered as one of the important causes of drought and desertification. It is very important to understand the multi-year variation and occurrence characteristics of drought in the Mongolian Plateau to explore the ecological environment and the response mechanism of surface materials to climate change. This study examines the spatio-temporal variations in drought and its frequency of occurrence in the Mongolian Plateau based on the Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) (1982–1999) and the Moderate-resolution Imaging Spectroradiometer (MODIS) (2000–2018) datasets; the Temperature Vegetation Dryness Index (TVDI) was used as a drought evaluation index. The results indicate that drought was widespread across the Mongolian Plateau between 1982 and 2018, and aridification incremented in the 21st century. Between 1982 and 2018, an area of 164.38 × 10⁴ km²/yr suffered from drought, accounting for approximately 55.28% of the total study area. An area of approximately 150.06 × 10⁴ km² (51.43%) was subject to more than 160 droughts during 259 months of the growing seasons between 1982 and 2018. We observed variable frequencies of drought occurrence depending on land cover/land use types. Drought predominantly occurred in bare land and grassland, both of which accounting for approximately 79.47% of the total study area. These terrains were characterized by low vegetation and scarce precipitation, which led to frequent and extreme drought events. We also noted significant differences between the areal distribution of drought, drought frequency, and degree of drought depending on the seasons. In spring, droughts were widespread, occurred with a high frequency, and were severe; in autumn, they were localized, frequent, and severe; whereas, in summer, droughts were the most widespread and frequent, but less severe. The increase in temperature, decrease in precipitation, continuous depletion of snow cover, and intensification of human activities have resulted in a water deficit. More severe droughts and aridification have affected the distribution and functioning of terrestrial ecosystems, causing changes in the composition and distribution of plants, animals, microorganisms, conversion between carbon sinks and carbon sources, and biodiversity. We conclude that regional drought events have to be accurately monitored, whereas their occurrence mechanisms need further exploration, taking into account nature, climate, society and other influencing factors.