Abstract
The variation in net primary productivity (NPP) and its controlling factors are crucial for understanding the mechanisms that maintain terrestrial ecosystem under ongoing climate and land cover change. However, such knowledge is still deficient in Central Asia where vegetation may be subjected to different drought stress. To achieve this goal, our study quantitatively explored the NPP variations and the mechanisms under different drought stress in Central Asia from 1990 to 2020 using Google Earth Engine with the Landsat datasets and environmental data. And a new method was introduced using NPP model to distinguish climate NPP (CNPP), and land cover NPP (LCNPP), affected by climate change, and land cover change, respectively. The results showed that vegetation productivity exhibited an increasing trend from 1990 to 2020, with the value of 473.61 Tg C and 522 Tg C in 1990 and 2020, respectively. The NPP in semi-arid, and dry sub-humid zones respectively increased by 12.94% and 33.78%, while NPP change in arid zones was not significant. The CNPP and LCNPP in Central Asia were -2.84×103 t C and 102.4×103 t C, respectively. In particular, land cover change significantly accumulated terrestrial productivity in the semi-arid zones, with the value of 66.44×103 t C. Climate conditions in arid and dry sub-humid zones respectively contributed 1.85×103 t C and 0.7×103 t C, but led to a decrease of 5.39×103 t C in dry sub-humid zones. NPP change in Central Asia was more sensitive to precipitation (R=0.72) than to temperature (R=-0.06) and solar radiation (R=-0.44). Additionally, the major limiting conditions in arid, and semi-arid zones both were precipitation, while the temperature was the key factor for vegetation growth in dry sub-humid ecosystems. In general, the impact of land cover change on vegetation productivity was higher than that of climate variations in Central Asia between 1990 and 2020.
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