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A great dust storm occurred in Tehran on 2 June 2014 and caused severe damage to properties and involved loss of human life. From the visual evidence available, it can be regarded as a case of haboob. As a lower latitude phenomenon, its occurrence in Tehran was unprecedented in the last 50 years. This paper aims to present a detailed analysis of the weather conditions, the pathways by which dust particles were ingested by the haboob, as well as the impact of the urban boundary layer on the intensity and propagation of the dust storm. Using numerical simulation carried out by the WRF-Chem model and various observational techniques, the coupling of a low-level small-scale deformation field with a lower-tropospheric cold pool produced by precipitating mid-tropospheric clouds is identified as the main process involved in shaping this rare dust storm. [ABSTRACT FROM AUTHOR]

Climate 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. [ABSTRACT FROM AUTHOR]

The Aral Sea basin (ASB) is one of the most environmentally vulnerable regions to climate change and human activities. During the past 60 years, irrigation has greatly changed the water distribution and caused severe environmental issues in the ASB. Using remote sensing data, this study investigated the environmental changes induced by irrigation activities in this region. The results show that, in the past decade, land water storage has significantly increased in the irrigated upstream regions (13 km³ year-1) but decreased in the downstream regions (-27 km³ year-1) of the Amu Darya River basin, causing a water storage decrease in the whole basin (-20 km³ year-1). As a result, the water surface area of the Aral Sea has decreased from 32,000 in 2000 to 10,000 km² in 2015. The shrinking Aral Sea exposed a large portion of the lake bottom to the air, increasing (decreasing) the daytime (nighttime) temperatures by about 1 °C year-1 (0.5 °C year-1). Moreover, there were other potential environmental changes, including drier soil, less vegetation, decreasing cloud and precipitation, and more severe and frequent dust storms. Possible biases in the remote sensing data due to the neglect of the shrinking water surface area of the Aral Sea were identified. These findings highlight the severe environmental threats caused by irrigation in Central Asia and call attention to sustainable water use in such dryland regions. [ABSTRACT FROM AUTHOR]

Determination of dust loading in the atmosphere is important not only from the public health point of view, but also for regional climate changes. The present study focuses on the characteristics of two major dust events for two urban areas in Iran, Kermanshah and Tehran, over the period of 4 years from 2006 to 2009. To detect extreme dust outbreaks, various datasets including synoptic data, dust concentration, reanalysis data and numerical results of WRF and HYSPLIT models were used. The weather maps demonstrate that for these events dusts are mainly generated when wind velocity is high and humidity is low in the lower troposphere and the region is under the influence of a thermal low. The event lasts until the atmospheric stability prevails and the surface wind speed weakens. The thermal low nature of the synoptic conditions of these major events is also responsible for deep boundary layer development with its thermals affecting the vertical dust flux over the region. Trajectory studies show that the dust events originated from deserts in Iraq and Syria and transported towards Iran. The main distinction between the two types of mobilizations seems to affect the dust concentrations in the Tehran urban area. [ABSTRACT FROM AUTHOR]

Based on dust storm records and meteorological data from six stations in the area surrounding the Tengger Desert over the period 1960-2007, the diurnal, monthly and interannual variation of dust storms and severe dust storms, as well as their relation to wind speed, precipitation and temperature, are analyzed and discussed. Statistical analyses demonstrate that such storms occur more frequently from 9:00 to 21:00 local standard time and much more frequently between March and May, especially April. Dust storm frequency (DSF) and severe dust storm frequency (SDSF) show a significant linear decreasing trend from 1960 to 2007. For monthly variability, winds (especially strong ones with speeds 10-20 m/s) are the main factor controlling both dust storm types. Precipitation and temperature have an indirect effect on DSF and SDSF by controlling vegetation growth. For interannual variability, strong wind is still the main control, with precipitation a relatively important cofactor. Temperature has an irregular but somewhat negative relationship with dust storms. Precipitation and especially temperature have likely been important in the increase of DSF since 2000. [ABSTRACT FROM AUTHOR]

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