Weakened dust activity over China and Mongolia from 2001 to 2020 associated with climate change and land-use management

Abstract

Dust cycle is actively involved in the Earth’s climate and environmental systems. However, the spatiotemporal pattern and recent trend of dust emission from the drylands in East Asia remain unclear. By calculating dust aerosol optical depth (DOD) from the newly released MODIS aerosol products, we obtain a relatively long satellite-based time series of dust activity from 2001-2020 over China and Mongolia. We identify pronounced interannual variability of dust activity that is consistent with ground-based meteorological observations in the study area. A substantial reduction in spring dust activity in northern China is also found, which seems in accordance with the long-term weakening trend since the 1970s that has been attributed to the wind speed decline by previous studies. However, the spatial pattern of the trends in both annual mean and seasonal dust activity during the last twenty years is divergent, and the most significant dust diminishing is found over north-central China where large-scale vegetation restoration projects have been implemented. It indicates that in addition to the potential contribution of wind speed change, land-use change also plays an important role in the recent inhibition of dust emission. The current results show that dust activity occurs most intensively in spring, followed by summer and relatively weaker in autumn and winter. However, dust activity in autumn and winter have been increased significantly in NW China despite the overall decreasing trend in other two seasons, probably associated with different seasonal atmospheric and land surface conditions. Finally, the DOD distribution reveals that the Tarim Basin, Gobi and Qaidam Basin Deserts are three major dust sources in East Asia. Compared to ground observations which are spatially limited and distributed unevenly, remote sensing provides an important complement, and it can serve as reference for identification of dust sources using other methods such as geochemical fingerprint and modeling.

Impact of Sea Surface Temperature Variability at Different Ocean Basins on Dust Activities in the Gobi Desert and North China

“…This decreasing trend has been documented by previous studies (Qiu et al, 2001;J. Yang et al, 2021) and can be attributed to a large-scale wind speed decline (Guan et al, 2017; S. S. Wang et al, 2021) and ecological restoration programs (Long et al, 2018; S. S. Wang et al, 2021) in North China. The seasonal cycle of DAF in these two regions exhibits similar features, with a significant peaking in spring (MAM) and a secondary peak in late fall (SON), consistent with previous studies (Guan et al, 2017; T. G. Yuan et al, 2016).…”

“…The dust activities affecting North China mainly come from the Gobi Desert (Tong et al., 2022; T. G. Yuan et al., 2016; K. Zhang et al., 2005), where dust optical depth is over 0.1 (S. S. Wang et al., 2021). Considering the different underlying surface types, climate types, most‐related meteorological elements, and mechanisms of sand emission in the Gobi Desert and transport in North China (Merrison, 2012), we separately consider the dust source area and dust transport area in this study by defining the dust source area that primarily lies in the central part of the Gobi Desert (37°N‐48°N, 95°E−110°E) and the dust transport area that covers North China (35°N‐45°N, 110°E‐125°E).…”

Drivers of recent decline in dust activity over East Asia

“…Dust activity in this region has decreased greatly since the 1970s 5 – 8 . The decline has been more remarkable in the last two decades after the dusty period of 2000-2002 9 – 12 . This decrease in dust activity has been beneficial to Chinese, enabling the People’s Republic to focus more on combating the anthropogenic air pollution in the 2010s 13 .…”

“…These programs have resulted in improved vegetation cover in some dust source regions, as evidenced from satellite observations 14 , 15 . Despite the synchronous occurrence of reduced dust activity and ecological restoration, there has been a debate on whether the ecological restoration programs have played a critical role in reducing the dust activity 12 , 16 – 18 . While it is expected that ecological restoration can reduce the dust activity, to what extent this effect is compared to the broad effect of climate change remains unclear.…”

“…For the attribution of the decline in dust activity, a quantitative assessment of the impacts from the various influencing factors is necessary. While several statistical analyses 5 – 7 , 11 , 12 suggest that several factors, including surface wind speed, vegetation cover, and soil wetness, influenced dust variations in the past decades in East Asia, it has been difficult to quantify the contributions of the individual factors as they are intermingled together 18 . For a quantitative assessment, it is vital to rely on numerical models as they represent the non-linear impacts of relevant factors on the movements of dust particles in a physical manner 2 – 4 , 8 , 9 .…”