Aeolian dust in Central Asia: Spatial distribution and temporal variability

Highlights

• Blowing dust and dust storm dominated the dust weather in Central Asia.

• Dust event frequency around the Aralkum, Caspian Depression and Kara-Bogaz-Gol region increased from the 1980s–2010s.

• Aeolian dust is gradually active in the Aralkum Desert from 1984 to 2018.

Abstract

Aeolian dust is a significant factor influencing the atmospheric environment in arid and semi-arid areas, and one which deeply involves biogeochemical cycling, energy exchange, and the global carbon balance. In this study, we investigated the synoptic features of atmospheric dust in the inland region of Central Asia and analyzed its spatiotemporal variation using meteorological observation records, satellite products from the Multi-angle Imagine SpectroRadiometer (MISR), and land use and land cover (LULC) data. Results showed that aeolian dust in Central Asia is particularly significant in the arid Aral Sea region where annual average dust event frequency reached 56 d during 1984–2018. Blowing dust and intense dust storms dominated the aeolian dust weather in Central Asia, which may severely affect the regional atmospheric environment and local inhabitants' health. Dust events occurred frequently in the Aralkum Desert, Kyzylkum Desert, Caspian Depression, Kara-Bogaz-Gol and, generally, along the southern and southeastern borders of Central Asia in spring, summer and autumn seasons; such events resulted in both high particulate matter (PM) concentrations and high dust deposition rates. Meanwhile, aeolian dust event frequency around the Aralkum Desert area, Caspian Depression, and Kara-Bogaz-Gol region increased gradually from the 1980s–2010s. The Aral Sea region's Aralkum Desert is the chief dust source in the Central Asian region, emitting vast quantities of saliferous mineral dusts that are then transported into East Asia by strong westerly jets.

Introduction

Mineral dust is of great significance to the Earth's biogeochemical cycle and carbon balances (Shao et al., 2011; IPCC, 2013; Huang et al., 2017; Mahowald et al., 2017). Over the past several decades, Asian dust has been an environmental concern which has received increased attention (Liu et al., 2004; Uno et al., 2009; Shao et al., 2013; Huang et al., 2014; Kaskaoutis et al., 2015; Rashki et al., 2018). Concrete evidence indicates that Asian dust, originating from the Gobi and other deserts, can be transported across both the North Pacific and North America in a global circuit (Wake et al., 1994; Mahowald et al., 2005, 2006; Uno et al., 2009; Zhang et al., 2018). These transport processes also influence atmospheric ice cloud nucleation and radiation balance (Carslaw et al., 2013; Yuan et al., 2019). However, our understanding of the variation in aeolian dust emissions in Central Asia and other arid and semiarid regions is still inadequate (Xi and Sokolik, 2016; Rashki et al., 2018; Shi et al., 2019; Yuan et al., 2019). At present, this inland continental area of Central Asia is at risk of severe desertification, due to global climate change, and consequently is at risk for more intense sand and dust storms (Ge et al., 2016; Li and Sokolik, 2018; Shi et al., 2019). Therefore, a detailed spatiotemporal analysis of Central Asian atmospheric dust is a timely contribution to promote a better understanding of the global dust cycle and its potential role in, and response to, climate change.

Aeolian dust storms are common weather phenomena in arid and semi-arid regions (Huang et al., 2017; Rashki et al., 2017). Fine dust particles emitted from desert sources can readily be suspended in the atmosphere and thus transported to distant areas by strong winds (Shao, 2000; Shao et al., 2011; Rashki et al., 2013; Issanova et al., 2013). Central Asia is an inland arid and semi-arid area which, as a region, suffers frequent wind-blown dust events (Indoitu et al., 2012; Miller-Schulze et al., 2015). The Aralkum, Karakum, Kyzylkum, Pre-Balkhash, and Caspian Lowland (Caspian Depression) deserts and the Kara-Bogaz-Gol region are the main dust sources of the Central Asian region (Indoitu et al., 2012; Shen et al., 2016; Issanova and Abuduwaili, 2017). It has been estimated that the above dust sources in Central Asia may contribute to 17–20% of global dust emissions (Xi and Sokolik, 2015). These dust events have mainly occurred in spring and summer, and resulted in aeolian dust event frequency of over 40 d yr⁻¹ (Indoitu et al., 2012). According to the trend analysis made by Indoitu et al. (2012), dust event frequency over Central Asia varied significantly, showing a high level during 1936–1960, then decreasing to 1980, and decreasing further into the late 20th century. Table 1 lists recent studies observing aeolian dust in Central Asia. Dust event frequency, dust deposition, and dust concentration were monitored and observed. It is notable that the observed dust depositions in Central Asia can approach as high as 8.4 kg m⁻² yr⁻¹, which is the highest recorded around the world (Groll et al., 2013; Zhang et al., 2017).

Aeolian dust events, such as dust storms, are closely associated with atmospheric dynamics (Shao, 2000; Liu et al., 2004; Kaskaoutis et al., 2015, 2016). Several atmospheric parameters such as El Niño-Southern Oscillation (ENSO), Arctic Oscillation and North Atlantic Oscillation (AO/NAO), and Siberian High (SH) can directly and/or indirectly influence dust activity over Central Asia (Huang et al., 2011; Groll et al., 2013; Shi et al., 2019). ENSO and drought anomaly over Central Asia are correlated with more active dust events (Barlow et al., 2002; Xi and Sokolik, 2015). The teleconnection between AO/NAO and dust activity in Central Asia occurs mainly through regulation of the winter SH (Gong et al., 2006; Groll et al., 2013). The SH is weaker (stronger) if the AO/NAO was in its positive (negative) phase (Gong and Ho, 2002; Gong et al., 2006). During the winter and spring season, SH caused the cold air intrusion over Central Asia, while high pressure over the Caspian Sea controlled the dust activity in summer (Orlovsky et al., 2005; Shi et al., 2019). Kaskaoutis et al. (2018) proposed the Caspian Sea-Hindu Kush Index (CasHKI), defined as the pressure gradient between the Caspian Sea High and the Hindu Kush Low, and identified it as the main factor influencing dust activity over the Karakum Desert. Thus, CasHKI may serve as an indicator of aeolian dust over the Central/South Asian region. Also, the orographic influence of the uplift of Tibetan Plateau (TP) acting on the Central Asian circulation patterns has been confirmed, and as such may intensify aridification of Central Asia (Guo et al., 2002; Chen et al., 2008; Groll et al., 2013).

The issue of Central Asian dust has attracted broad scientific interest due to its associated interactions with socioeconomics, human health, and ecosystems (Groll et al., 2013; Goudie, 2014; Indoitu et al., 2015). For example, due to overuse of water resources, the Aral Sea, located between Uzbekistan and Kazakhstan (Fig. 1), over the last century has shrunk by >90% (Micklin, 2007; Indoitu et al., 2012; Opp et al., 2017; McDermid and Winter 2017). As a result the Aralkum Desert, one of the world's youngest deserts and another Asian dust source, has formed there (Breckle et al., 2012; Indoitu et al., 2012; Groll et al., 2013; Issanova et al., 2015; Opp et al., 2017; Shen et al., 2016; Zhang et al., 2017). Since the 1990s, the international community has recognized the demise of the Aral Sea as the largest man-made ecological disaster on the planet (Micklin, 2007; Groll et al., 2013). Incidences of respiratory diseases, such as pneumonia, have increased due to the intensification of processes of soil salinization and land degradation (Indoitu et al., 2012; Issanova and Abuduwaili, 2017). Thus, aeolian dust in Central Asia is not only of interest within the physical sciences but is also a concern for human welfare and ecological stability. In addition, land over-exploitation can exacerbate the ecological vulnerability to aeolian wind erosion. Agricultural activity is constantly expanding in Central Asia where the area under irrigation increased by 40.6% from 1918 to 1960 (Dukhovny and de Schutter, 2011). Central Asia has experienced significant land cover and land use changes, driven by both anthropogenic activity and natural forces. These changes have led to recognition of the impact of global change on aeolian dust activity as a contemporary issue.

Recently, international scientific communities and intergovernmental organizations have realized the urgency of dealing with the above problems in Central Asian regions. This study is motivated by the foregoing reasons to investigate the latest spatiotemporal characteristics of aeolian dust over Central Asia. Based upon meteorological observation records from 70 stations for the period of 1984–2018, Multi-angle Imagine SpectroRadiometer (MISR) satellite data, and land use and land cover (LUCC) data, we systematically studied the spatiotemporal variation in the frequency of dust events (defined in section 2.2), ranging from dust in suspension, blowing dust, dust storm, and severe dust storm. Further discussion of the associated potential effects of aeolian dust has been conducted. This work seeks to improve our understanding of dust mobilization, transport, and deposition in Central Asian regions.