Dust Storm Frequency Research Articles

Isotopic constraints on the formation pathways and sources of atmospheric nitrate in the Mt. Everest region

Inorganic particulate nitrate (p-NO3−), gaseous nitric acid (HNO3(g)) and nitrogen oxides (NOx = NO + NO2), as main atmospheric pollutants, have detrimental effects on human health and aquatic/terrestrial ecosystems. Referred to as the ‘Third Pole’ and the ‘Water Tower of Asia’, the Tibetan Plateau (TP) has attracted wide attention on its environmental changes. Here, we evaluated the oxidation processes of atmospheric nitrate as well as traced its potential sources by analyzing the isotopic compositions of nitrate (δ15N, δ18O, and Δ17O) in the aerosols collected from the Mt. Everest region during April to September 2018. Over the entire sampling campaigns, the average of δ15N(NO3−), δ18O(NO3−), and Δ17O(NO3−) was −5.1 ± 2.3‰, 66.7 ± 10.2‰, and 24.1 ± 3.9‰, respectively. The seasonal variation in Δ17O(NO3−) indicates the relative importance of O3 and HO2/RO2/OH in NOx oxidation processes among different seasons. A significant correlation between NO3− and Ca2+ and frequent dust storms in the Mt. Everest region indicate that initially, the atmospheric nitrate in this region might have undergone a process of settling; subsequently, it got re-suspended in the dust. Compared with the Δ17O(NO3−) values in the northern TP, our observed significantly higher values suggest that spatial variations in atmospheric Δ17O(NO3−) exist within the TP, and this might result from the spatial variations of the atmospheric O3 levels, especially the stratospheric O3, over the TP. The observed δ15N(NO3−) values predicted remarkably low δ15N values in the NOx of the sources and the N isotopic fractionation plays a crucial role in the seasonal changes of δ15N(NO3−). Combined with the results from the backward trajectory analysis of air mass, we suggest that the vehicle exhausts and agricultural activities in South Asia play a dominant role in determining the nitrate levels in the Mt. Everest region.

A new integrated data mining model to map spatial variation in the susceptibility of land to act as a source of aeolian dust

This research developed a more efficient integrated model (IM) based on combining the Nash-Sutcliffe efficiency coefficient (NSEC) and individual data mining (DM) algorithms for the spatial mapping of dust provenance in the Hamoun-e-Hirmand Basin, southeastern Iran. This region experiences severe wind erosion and includes the Sistan plain which is one of the most PM2.5-polluted regions in the world. Due to a prolonged drought over the last two decades, the frequency of dust storms in the study area is increasing remarkably. Herein, 14 factors controlling dust emissions (FCDEs) including soil characteristics, climatic variables, digital elevation map, normalized difference vegetation index, land use and geology were mapped. Correlation and collinearity among the FCDEs were examined by the Pearson test, tolerance coefficient (TC) and variance inflation factor (VIF), with the results suggesting a lack of collinearity between FCDEs. A tree-based genetic algorithm was applied to prioritize and quantify the importance weights of the FCDEs. Thirteen individual data mining models were applied for mapping dust provenance. The model performance was assessed using root mean square error, mean absolute error and NSEC. Based on clustering analysis, the 13 DM models were grouped into five clusters and then the cluster with the highest NSEC values used in an integrated modelling process. Based on the results, the IM (NSEC = 93%) outperformed the individual DM models (the NSEC values range between 51 and 92%). Using the IM, 11, 5, 7 and 77% of the total study area were classified into low, moderate, high and very high susceptibility classes for dust provenance, respectively. Overall, the results illustrate the benefits of an IM for mapping spatial variation in the susceptibility of catchment areas to act as dust sources.

Weakening Dust Storm Intensity in Arid Central Asia Due to Global Warming Over the Past 160 Years

Dust storms occur frequently in arid central Asia (ACA) and greatly influence the regional ecology/environment, human health and security, as well as the global climate. To date, neither the patterns nor the underlying mechanisms of dust storms in ACA are fully understood, partly due to the lack of long term historical records. Here we reconstruct a dust storm history of the past ~160 years in northwest China, based on high resolution sedimentary proxies retrieved from Lake Karakul (located in the core zone of ACA). We find that changes in the sedimentary coarse fraction (grainsize >64μm) in Lake Karakul are correlated with both historical and modern observed dust storms. The reconstructed dust storm intensity shows a decreasing trend since AD 1850s, with three high occurrence intervals at AD 1870s-1910s, AD 1930s-1940s, and AD 1960s-1980s. We contend that changes in temperature and wind speed could have dominated the frequency and intensity of dust storms in northwest China during the record periods: temperature controls the wind speed and then the dust storm frequency/intensity; lower temperature corresponding to higher wind speed, and higher dust storm frequency/intensity, and vice versa. The observed anthropogenic global warming could have led to decrease in atmospheric temperature gradients and decline in wind speed, and then decreasing dust storm frequency/intensity. Providing this stands, less and weaker dust storms are expected under a continuously anthropogenic warming scenario.

Classification of aerosols over Saudi Arabia from 2004–2016

Knowledge of aerosol size and composition is very important for investigating the radiative forcing impacts of aerosols, distinguishing aerosol sources, and identifying harmful particulate types in air quality monitoring. The ability to identify aerosol type synoptically would greatly contribute to the knowledge of aerosol type distribution at both regional and global scales, especially where there are no data on chemical composition. In this study, aerosol classification techniques were based on aerosol optical properties from remotely-observed data from the Ozone Monitoring Instrument (OMI) and Aerosol Robotic Network (AERONET) over Saudi Arabia for the period 2004–2016 and validated using data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). For this purpose, the OMI-based Aerosol Absorption Optical Depth (AAOD) and Ultra-Violet Aerosol Index (UVAI), and AERONET-based AAOD, Ångström Exponent (AE), Absorption Ångström Exponent (AAE), Fine Mode Fraction (FMF), and Single Scattering Albedo (SSA) were obtained. Spatial analysis of the satellite-based OMI-AAOD showed the dominance of absorbing aerosols over the study area, but with high seasonal variability. The study found significant underestimation by OMI AAOD suggesting that the OMAERUV product may need improvement over bright desert surfaces such as the study area. Aerosols were classified into (i) Dust, (ii) Black Carbon (BC), and (iii) Mixed (BC and Dust) based on the relationships technique, between the aerosol absorption properties (AAE, SSA, and UVAI) and size parameters (AE and FMF). Additionally, the AE vs. UVAI and FMF vs. UVAI relationships misclassified the aerosol types over the study area, and the FMF vs. AE, FMF vs. AAE and FMF vs. SSA relationships were found to be robust. As expected, the dust aerosol type was dominant both annually and seasonally due to frequent dust storm events. Also, fine particulates such as BC and Mixed (BC and Dust) were observed, likely due to industrial activities (cement, petrochemical, fertilizer), water desalination plants, and electric energy generation. This is the first study to classify aerosol types over Saudi Arabia using several different aerosol property relationships, as well as over more than one site, and using data over a much longer time-period than previous studies. This enables classification and recognition of specific aerosol types over the Arabian Peninsula and similar desert regions.

An Investigation of Vertically Distributed Aerosol Optical Properties over Pakistan Using CALIPSO Satellite Data

The vertically distributed aerosol optical properties are investigated over Pakistan utilizing the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Level 2 products from 2007 to 2014. For a better understanding of the spatiotemporal characteristics of vertical aerosol layers, the interannual and seasonal variations of nine selected aerosol parameters such as the AOD of the lowest aerosol layer (AODL), the base height of the lowest aerosol layer (HL), the top height of the highest aerosol layer (HH), the volume depolarization ratio of the lowest aerosol layer (DRL), the color ratio of the lowest aerosol layer (CRL), total AOD of all the aerosol layers (AODT), the number of aerosol feature layers (N), the thickness of the lowest aerosol layer (TL), the AOD proportion for the lowest aerosol layer (PAODL) for both day and night times are analyzed. The results show AODT increased slightly from 2007 to 2014 over Pakistan, and relatively high AODT exists over the Punjab and Sindh (southern region), which might be owing to the high level of economic development, frequent dust storms, and profound agricultural activities (anthropogenic emissions). AODT increases from north to south. The reason may be that the southern region is rapidly urbanized and is near the desert. The northern region is dominated by agricultural land, and cities are usually semi-urbanized. The highest AODT appears in summer compared to the other seasons, and during daytime compared to nighttime. The HL and HH vary significantly, owing to the topography of Pakistan. The N is relatively large over Punjab and Sindh compared to the other regions, which might be caused by relatively stronger atmospheric convections. The spatial distribution of the TL showed an inverse relationship with the topography as lower values are observed over elevated regions such as Gilgit-Baltistan and Jammu-Kashmir. The value of the PAODL indicates that 77% of the total aerosols are mainly concentrated in the lowest layer of the atmosphere over Pakistan. The higher values of DRL and CRL indicate non-spherical and large particles over Balochistan and Sindh, which might be related to the proximity to the desert. This study provides very useful information about vertically distributed aerosol optical properties which could help researchers and policymakers to regulate and mitigate air pollution issues of Pakistan.

Dust storm frequency change in relation to climate drivers

AbstractClimate variability and change in arid regions are important factors in controlling emission, frequency and movement of dust storms. This study provides robust statistical methods including univariate Mann‐Kendall block bootstrapping method and three bivariate trend assessment methods, Covariance Inversion Test, Covariance Sum Test and The Covariance Eigenvalue to detect trends in dust storm frequency across arid regions of Iran in relation to climate variability and trend in recent decades. In this regard, the annual number of dust storms from 25 stations in central arid and semi‐arid regions of Iran were selected. In addition, five major climatic variables including annual rainfall, annual maximum and average wind speed, annual maximum and average temperature were also collected. The univariate trend test indicates both increasing and decreasing trend in dust storm frequency and climate variables. The bivariate trend test shows a strong and statistically significant relationship between trend of climate variables and dust storm frequency for most of the stations across the region. Among climate variables, rainfall change has an inverse impact on dust storm frequency while wind speed and temperature have direct covariance structure with dust storm frequency. The wind speed also seems to be the most effective climate driver on dust storm frequency in arid regions of Iran, followed by temperature. The results also shows that local conditions that are not considered in this study may also play a significant role in dust storm emission in some parts of the region.

Using composite fingerprints to quantify the potential dust source contributions in northwest China

Dust storms have a profound impact on the atmospheric environment, global climate change, and human health, so it is of great importance to strengthen related research. The main areas of occurrence and frequency of dust storms in northwestern China were distinguished by measuring the concentration of geochemical elements in the topsoil and atmospheric dust samples, combined with the HYSPLIT backward trajectory model, MODIS true-color satellite images, and PM10 real-time monitoring data. On this basis, the composite fingerprints method was used to establish an end-member model between the concentration of dust storm samples and topsoil samples, and then to trace the sand and dust sources in northwest China and quantify their source contributions. The results showed that the main potential source areas causing sandstorms were located in the Kumtag Desert, Hexi area, and the Gobi Desert in the central and western parts of Inner Mongolia. Overall, the contributions from natural sources were greater than those from anthropogenic sources, especially at Alxa League. In addition to natural sources, anthropogenic dust sources contributed highly to dust storms, with a contribution rate of approximately 40% in cities. The main dust source in Zhangye City was from agriculture areas. The contribution of the potential dust sources in the west of the study area showed a decreasing trend from west to east because of the distance effect. Because of the influence of the prevailing westerly winds in the east, the sources of dust were relatively extensive. The Badain Jaran Desert and Tengger Desert were not the main dust sources in the study area because of artificial sand control measures and the low amounts of fine-grained components in sandy deserts. These methods and results are of great importance for sustainable development in northwest China.

Source routing and detection of dust storm in the Salt Lake basin of Qom in Iran

In the last decades, the frequency of dust storms has increasingly emerged in the central regions of Iran. This study investigated the SDS sources in the Salt Lake basin of Qom using daily visibility, wind speed, dust weather codes and NCEP/NCAR data, and MODIS and Sentinel-1 sensor datasets. Sample SDS days were selected by daily visibility and dust weather codes with 3-h interval ranging from 2000 to 2017. These sample SDS days were related to the 19 synoptic stations of the Salt Lake basin. Dust entry trajectories were determined through the HYSPLIT model and evaluated with the MODIS Deep Blue aerosol optical depth and atmospheric patterns. SDS sources were identified using Sentinel-1 radar images of IW mode and SLC type through radar interferometry technique. Analysis of variability and frequency in dusty days and wind speed indicated that in high wind speed and dusty days, frequency increases in the second half of the course. SDS entry trajectories indicated that the SDS mainly entered in the study area during April and May from Iraq and eastern Syria and also during June and July from the east of Iran and the study basin. Study of the regional atmospheric circulation represented that the thermodynamic relationship between the thermal low pressure and trough at 500 hPa in spring provides instability and ascending air in Iraq and eastern Syria. In summer, the pressure gradient between thermal low pressure in the east of Iran and the Caspian high pressure intensifies the wind in the eastern part of Iran from the surface to 850 hPa level. Investigation of the dust pickup areas with radar interferometry technique revealed that as far as Iraq and eastern Syria were concerned, the eastern part of Al-Anbar province in the western desert of Iraq was the first source, desert areas in central and southern Iraq were the second source, and the eastern part of Syria ranked the third source of dust. In Iran, the main sources of SDS are located in the eastern regions of the Salt Lake basin as newfound region, the southeastern areas of Semnan province, the northwest of Yazd, and the northeast of Isfahan in the central desert of Iran. In recent years, there has been more abundance of dust originated from the eastern SDS trajectories.

Temporal fluctuations of PM2.5 and PM10, population exposure, and their health impacts in Dezful city, Iran.

Morbidity and mortality impacts of particulate matter (PM) are globally important health critical parameters. In this ecological-descriptive study, the health impact of PM10 and PM2.5 associated with there temporal variations in Dezful city were assessed from 2013 to 2015. AirQ+ software handles the PM air pollutants by addressing impact evaluation and life table evaluation. We used a new method to analysis fine particles feature by using regular daily observations of PM10. In this method, relationship between PM2.5 and PM10 mass concentrations were analyzed and calculated. The annual average concentrations of PM10 were 147.1, 114.3 and 158.8μg/m3, and the annual average concentration of PM2.5 were 57.8, 50.7 and 58.2μg/m3 in 2013, 2014 and 2015, respectively. PM10 also had obvious diurnal variations with highest hourly concentrations in 13:00 and 22:00 but the lowest concentrations often occurred in 05:00 and 16:00. Unexpectedly, in weekends the concentration of PM pollutants appeared to have increased from 18:00 to midnight. The daily based analysis showed that there are 147 dusty days in the study period during which the most severe dusty day occurred in 2014. Over the study period, mean levels of PM10 and PM2.5 in both conditions were higher in 2015 compare to 2013 and 2014, which probably is due to higher frequency of dust storms in 2015. Hence, during 2015 and 2013 they're were higher morbidity and mortality compare to 2014 due to exposure to higher polluted air with PMs in all cases except lung cancer (LC).

Air pollution characteristics and human health risks in key cities of northwest China

Air pollution events occur frequently in northwest China, which results in serious detrimental effects on human health. Therefore, it is essential to understand the air pollution characteristics and assess the risks to humans. In this study, we analyzed the pollution characteristics of criteria pollutants in six key cities in northwest China from 2015 to 2018. We used the air quality index (AQI), aggregate AQI (AAQI), and health-risk based AQI (HAQI) to assess the health risks and determine the proportion of people exposed to air pollution. Additionally, on this basis, the AirQ2.2.3 model was used to quantify the health effects of the pollutants. The results showed that PM10 pollution occurred mainly in spring and winter and was caused by frequent dust storms. PM2.5 pollution was caused mainly by anthropogenic activities (especially coal-fired heating in winter). Because of a series of government policies and pollutant reduction measures, PM2.5, SO2, NO2, and CO concentrations showed a downward trend during the study period (except for a small increase in the case of NO2 in some years.). However, O3 showed high concentrations due to the high intensity of solar radiation in summer and inadequate emission reduction measures. The air quality levels based on their classification were generally higher than the Chinese ambient air quality standard classified by the AQI index. We also found that the higher the AQI index was, the more serious the air pollution classified based on the AAQI and HAQI indices was. The HAQI index could better reflect the impact of pollutants on human health. Based on the HAQI index, 20% of the population in the study area was exposed to polluted air. The total mortality values attributable to PM10, PM2.5, SO2, O3, NO2, and CO, quantified by the AirQ2.2.3 model, were 3.00%, 1.02%, 1.00%, 4.22%, 1.57%, and 0.95% (Confidence Interval:95%), respectively; the attributable proportions of mortality for respiratory system and cardiovascular diseases were consistent with the change rule of total mortality, because the number of deaths attributable to the latter was greater than that for the former. According to the exposure reaction curves of pollutants, PM10 and PM2.5 still showed a large change at high concentrations. However, the tendencies of SO2, NO2, CO, and O3 were more obvious under low concentration exposure, which indicated that the expected mortality rate due to lower air pollution concentrations was much higher than the mortality due to high air pollution concentrations.

Joint Modeling of Severe Dust Storm Events in Arid and Hyper Arid Regions Based on Copula Theory: A Case Study in the Yazd Province, Iran

Natural disasters such as dust storms are random phenomena created by complicated mechanisms involving many parameters. In this study, we used copula theory for bivariate modeling of dust storms. Copula theory is a suitable method for multivariate modeling of natural disasters. We identified 40 severe dust storms, as defined by the World Meteorological Organization, during 1982–2017 in Yazd province, central Iran. We used parameters at two spatial vertical levels (near-surface and upper atmosphere) that included surface maximum wind speed, and geopotential height and vertical velocity at 500, 850, and 1000 hPa. We compared two bivariate models based on the pairs of maximum wind speed–geopotential height and maximum wind speed–vertical velocity. We determined the bivariate return period using Student t and Gaussian copulas, which were considered as the most suitable functions for these variables. The results obtained for maximum wind speed–geopotential height indicated that the maximum return period was consistent with the observed frequency of severe dust storms. The bivariate modeling of dust storms based on maximum wind speed and geopotential height better described the conditions of severe dust storms than modeling based on maximum wind speed and vertical velocity. The finding of this study can be useful to improve risk management and mitigate the impacts of severe dust storms.

Dust storm susceptibility on different land surface types in arid and semiarid regions of northern China

Dust storm originates from arid and semiarid areas and could cause worldwide lasting effects along varying trajectories. As an extreme weather hazard, dust storm is usually induced by strong winds. In this paper, an aerodynamic parameter, defined as the ratio between dust storm frequency (DSF) and strong wind frequency (SWF), was calculated for quantifying dust storm susceptibility (DSS). The characteristic value and temporal change of DSS in five typical land surface areas, including cultivated land, grassland, sand desert, Gobi desert, and salt crust, were analyzed with dust storm and strong wind records at 15 weather stations. The spatial distribution of DSS in the arid and semiarid regions of northern China was described using dust storm and strong wind records at 102 meteorological stations. There are positive correlations between SWF and DSF for any identical land surface type. Land surface conditions have a great influence on dust storm susceptibility. According to DSS value, the five land surface types can be divided into two categories: (1) Cultivated land and sand desert, with DSS between 0.64 and 0.53, about 2.6–10 times higher than that of the other three land surfaces, are prone to forming dust storm under strong wind conditions; (2) Gobi desert, grassland and salt crust, with average DSS from 0.06 to 0.2, exhibit lower probability of dust storm occurrence under strong wind conditions. The DSF in the surrounding areas of the arid Taklimakan desert in Xinjiang are much larger than SWF, and dust storms take place readily even at normal erosive wind conditions. The areas with high DSF are not spatially consistent with SWF distribution but more coincide with high DSS areas where sand deserts and farmland are concentrated. In the nearly four past decades, the DSS showed an overall increasing trend on different ground surfaces which may be related to local human activities and climatic warming.

Gaseous and heterogeneous reactions of low-molecular-weight (LMW) unsaturated ketones with O3: Mechanisms, kinetics, and effects of mineral dust in tropospheric chemical processes

Mineral dust has a significant effect on the atmospheric heterogeneous chemistry and environmental risk prediction of VOCs. In this work, a comprehensive theoretical study for the gaseous and heterogeneous reactions process of four Low-Molecular-Weight (LMW) unsaturated ketones with O3 has been provided for the first time. SiO2 is the main component of mineral dust, which shows better adsorption performance of these ketones and represents a good sinking of atmospheric LMW oxygenated VOCs. The gaseous reactions of LMW unsaturated ketones with O3 are closely related to the formation of some strong oxidants and air pollution behaviors. The heterogeneous reactions of these ketones onto the surface of available mineral aerosols may compete with the corresponding gas phase reactions, especially in arid and semi-arid areas with frequent dust storms. Organic hydroperoxides and LMW carbonyl compounds generated in the title reactions may change the properties of aerosols, which have essential impacts on tropospheric chemistry and climate. The presence of SiO2 could accelerate the reactions of LMW unsaturated ketones with O3 without changing their degradation mechanism. It also should be emphasized that the promoting effect of SiO2 clusters to CH2OO + H2O has been found in our computation. This may explain the high product yields of HMHP and H2O2 detected on SiO2 particles in the experiment. The effect of mineral particles on the O3-initiated reactions has been probed at the molecular level and the pollution mechanism of VOCs has been better understood.

Climatology of Iraqi dust events during 1980–2015

Mesopotamia in Iraq is exposed to dust events of different intensity because of adjacent extended desert or semi-desert areas. This study investigates the spatial–temporal distributions of dust events (including suspended dust, rising dust and dust storms) in Iraq by analysing dust observations based on visibility from seven meteorological stations supplied by the Iraqi Meteorological Organization (IMO) during 1980–2015. The annual and seasonal evaluation of all dust event frequencies is examined. The findings show that Iraq has been exposed to the maximum number of dust events in spring and summer seasons over the past 35 years. The dust was more active in summer compared with other seasons for the northern region of Iraq, while the south and central parts of Iraq are exposed to the largest frequency of dust storms in spring and summer. The cities near desert areas (e.g. Nasiriya, Basra and Baghdad) suffer from the greatest frequency of dust storms compared to the northern and eastern regions. According to the annual average during 1980–2015, the frequency of major dust storm activity in Nasiriya was 7.8 days, in Baghdad 3.1 days) and in Basra 2.3 days. Suspended dust is more frequent in Iraq compared with rising dust or dust storms. There was a greater frequency of dust events associated with high temperatures and wind speeds in the central and southern areas during summer. All three types of dust events show similar time trend distributions with three periods: increased frequency of dust between 1980 and 1993, decreased frequency during 1993–2001 and increased again from 2001.

Dust Events and Indoor Air Quality in Residential Homes in Kuwait.

Kuwait is a developed Middle Eastern country that is impacted by frequent dust storms from regional and/or remote deserts. The effectiveness of keeping homes tightly closed during these events to reduce dust exposures was assessed using indoor and outdoor particle samples at 10 residences within the metropolitan Kuwait City area. Specifically, this study compared indoor and outdoor levels of black carbon and 19 trace elements (Na, Mg, Al, Si, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Sr, and Zr) during dust and non-dust events and found that particle penetration efficiencies were lower during dust storm events (less than 20–30%) than during non-dust storm events (40–60%). Coarse particles had lower penetration efficiency compared to fine particles, which is due to differences in infiltration rates and settling velocities between these two size fractions. Our findings suggest that increasing home insulation could be an effective strategy to reduce indoor exposure to crustal particles from dust storm events in residential houses of Kuwait City.

Extratropical cyclones over the North Atlantic and western Europe during the Last Glacial Maximum and implications for proxy interpretation

Abstract. Extratropical cyclones are a dominant feature of the midlatitudes, as their passage is associated with strong winds, precipitation and temperature changes. The statistics and characteristics of extratropical cyclones over the North Atlantic region exhibit some fundamental differences between pre-industrial (PI) and Last Glacial Maximum (LGM) climate conditions. Here, the statistics are analysed based on results of a tracking algorithm applied to global PI and LGM climate simulations. During the LGM, both the number and the intensity of detected cyclones were higher compared to PI. In particular, increased cyclone track activity is detected close to the Laurentide ice sheet and over central Europe. To determine changes in cyclone characteristics, the top 30 extreme storm events for PI and LGM have been simulated with a regional climate model and high resolution (12.5 km grid spacing) over the eastern North Atlantic and western Europe. Results show that LGM extreme cyclones were characterised by weaker precipitation, enhanced frontal temperature gradients and stronger wind speeds than PI analogues. These results are in line with the view of a colder and drier Europe, characterised by little vegetation and affected by frequent dust storms, leading to reallocation and build-up of thick loess deposits in Europe.

Asian dust-storm activity dominated by Chinese dynasty changes since 2000 BP

The Asian monsoon (AM) played an important role in the dynastic history of China, yet it remains unknown whether AM-mediated shifts in Chinese societies affect earth surface processes to the point of exceeding natural variability. Here, we present a dust storm intensity record dating back to the first unified dynasty of China (the Qin Dynasty, 221–207 B.C.E.). Marked increases in dust storm activity coincided with unified dynasties with large populations during strong AM periods. By contrast, reduced dust storm activity corresponded to decreased population sizes and periods of civil unrest, which was co-eval with a weakened AM. The strengthened AM may have facilitated the development of Chinese civilizations, destabilizing the topsoil and thereby increasing the dust storm frequency. Beginning at least 2000 years ago, human activities might have started to overtake natural climatic variability as the dominant controls of dust storm activity in eastern China.

Sheltering effect of a multiple-row Tamarix windbreak – a field study in Niatak, Iran

The Sistan region in southeastern Iran is one of the country's main dust storm areas. To reduce the frequency and intensity of dust storms using efficient windbreaks is critical. In a field study the sheltering effect of a multiple-row windbreak (14 rows of Tamarix aphylla) in the Niatak area was evaluated by obtaining the vertical and horizontal values of Rc(x, z) (wind reduction coefficient) upwind (x=− 100), within (x=100 and 256) and downwind (x=448 and 560) of the windbreak. A slight deflection in the vertical profiles of the sheltering effect at a height ofz/h= 0.2–0.8, a significant increase in the Rc(x, z) values was observed within the windbreak that demonstrated the roughness influence of vegetation. The sheltering effect increased within the windbreak consistent with the increasing aerodynamic roughness length (z0). The greatest Rc(x, z) values was observed at the beginning of windbreak (x= 100), where the largest values of z0 occurred. At downwind distances of x=448 and 560 the values of Rc(x, z) were respectively greater and lower than upwind values, revealing the sheltering effect of the windbreak in an area 50 h beyond the vegetation. Significant sheltered areas (50 h beyond and 1.8 h above the windbreak) and reduced wind speeds (50% at x=100) by the windbreak and the location of minimum wind speed at the beginning of the windbreak demonstrates that the efficiency of the windbreak is optimum. This is mainly attributed to the optimal porosity (39%) and structure of the windbreak (multiple-row design).

Spatiotemporal variations and driving factors of dust storm events in northern China based on high-temporal-resolution analysis of meteorological data (1960–2007)

Northern China is a significant source of dust source in Central Asia. Thus, high-resolution analysis of dust storms and comparison of dust sources in different regions of northern China are important to clarify the formation mechanism of East Asian dust storms and predict or even prevent such storms. Here, we analyzed spatiotemporal trends in dust storms that occurred in three main dust source regions during 1960–2007: Taklimakan Desert (western region [WR]), Badain Jaran and Tengger Deserts (middle region [MR]), and Otindag Sandy Land (eastern region [ER]). We analyzed daily dust storm frequency (DSF) at the 10-day scale (first [FTDM], middle [MTDM], and last [LTDM] 10 days of a month), and investigated the association of dust storm occurrences with meteorological factors. The 10-day DSF was greatest in the FTDM (accounting for 77.14% of monthly occurrences) in the WR, MTDM (45.85%) in the MR, and LTDM (72.12%) in the ER, showing a clear trend of movement from the WR to the ER. Temporal analysis of DSF revealed trend changes over time at annual and 10-day scales, with mutation points at 1985 and 2000. We applied single-factor and multiple-factor analyses to explore the driving mechanisms of DSF at the 10-day scale. Among single factors, a low wind-speed threshold, high solar radiation, and high evaporation were correlated with a high DSF, effectively explaining the variations in DSF at the 10-day scale; however, temperature, relative humidity, and precipitation poorly explained variations in DSF. Similarly, multiple-factor analysis using a classification and regression tree revealed that maximum wind speed was a major influencing factor of dust storm occurrence at the 10-day scale, followed by relative humidity, evaporation, and solar radiation; temperature and precipitation had weak influences. These findings help clarify the mechanisms of dust storm occurrence in East Asia.

Satellite Monitoring of Natural Reforestation Efforts in China's Drylands

Summary Desertification in Northern China degrades air quality in China's eastern cities by causing frequent dust storms. To stop desert expansion, China's government initiated the Three-North Shelterbelt Program, a large-scale reforestation project. Many issues with the project have been raised, from the choice of ill-adapted species to planting methods. Recently, the government implemented “natural reforestation”—closing former pastures to let vegetation regrow naturally. Unfortunately, it has been difficult to estimate the large-scale success of natural reforestation because measuring arid ecosystem productivity is a challenge for optical remote sensing. Here, we use satellite data to monitor vegetation water content and photosynthetic activity, thereby quantifying changes in vegetation biomass and productivity in Northern China. These satellite data corroborate official reforestation data. Our results show that vegetation activity is strongly correlated with both natural and traditional active reforestation, indicating opportunities for new natural reforestation techniques combined with satellite monitoring in other semi-arid regions.