The standardized precipitation evapotranspiration index (SPEI), calculated from 55 stations over the period 1961-2015, was used to analyze the spatial and temporal variability of the dry and wet climate in Xinjiang on a three and six-month time scale, so as to help to actively deal with the negative effects of climate change and reduce disaster losses. The obtained results show that precipitation and temperature in Xinjiang have an increasing trend, with rates of 8.90 mm and 0.39 ºC per decade, respectively. SPEI-3 and SPEI-6 show the same linear change trend, with a change rate of 0.005 and 0.007 per decade, respectively. Severe droughts occurred in 1997 and 2008, and particularly in 2008 considering SPEI-6, the number of meteorological stations with moderate drought and extreme drought accounted for 60 % of all stations. Analysis of Empirical Orthogonal Function (EOF) indicates that SPEI-3 and SPEI-6 have similar spatial distribution in the three EOF modes. EOF1 reflects that the overall dry and wet changes in the study area were weakening, and there was a drying trend; EOF2 was a reverse change in the northern and Southern Xinjiang; EOF3 shows that the East Tianshan had a drying trend, while the western part of Southern Xinjiang had a moistening trend. The spectra of wavelet coherence and cross wavelet transform showed that the SPEI values in Xinjiang have resonance periods of different time scales with the Atlantic Multidecadal Oscillation (AMO), El Nino Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal oscillation (PDO), but shows differences in different time-domain correlations. Among them, AMO is the main atmospheric circulation factor that affects SPEI in the region.

Drought is a complex natural hazard that has numerous negative effects on ecosystems, agriculture, and the economy. For this reason, it is difficult to provide a precise definition. Nevertheless, different conceptualizations converge in one common denominator: the deficit of precipitation with respect to an average historical value. Droughts in Mexico have been recurrent and persistent, resulting from complex interactions of the atmosphere with the oceans and the geographic and physiographic characteristic of the country. Several researchers have approached this phenomenon with indices to characterize it using features such as intensity, duration and frequency. In this study we analyze droughts in a spatiotemporal context at scales of 3, 6, 12 and 24 months with SPI and SPEI indices at 19 weather stations located in middle and upper regions of the Sonora River basin, Mexico, for the period 1974-2013. The regions were defined according to mean annual rainfall behavior, applying statistical techniques and analyzing the physiographic characteristics of the study region. Results indicate that drought intensity increased at the end of the time series analyzed, and important periods were identified in the years 1997, 1999, 2000 and 2011 to 2013. SPEI defined the drought periods and the increasing intensity trend better than SPI, demonstrating the importance of including variables such as evapotranspiration in the balance of available water.

Urban areas are important contributors to the increase of global CO2 levels due to human activities, but continuous records of CO2 concentration in cities are scarce, especially in the developing world. In this study we present five years of simultaneous, in-situ measurements at a university campus in the south of Mexico City (UNAM) and at a high-altitude station, the Altzomoni atmospheric observatory (ALTZ), 60 km apart from the first site. The characteristics of the daily cycles, seasonality, and long-term trends were extracted from both time series. The features of the daily and seasonal cycles at UNAM are dominated by the dynamics of the boundary layer growth, while the seasonality at Altzomoni is determined by both the local meteorology and the photosynthetic activity of the vegetation. Annual CO2 growth rates of 2.4 and 2.6 ppm yr–1 were estimated for UNAM and Altzomoni, respectively, in close agreement with reported global growth rates and with previous estimates of total column CO2 trends. The simultaneous monitoring at the urban and the mountain sites revealed a regular exchange of air masses between the city and its vicinities. The annual cycle at UNAM shows a secondary CO2 maximum at the end of the dry season, the source of which is yet to be determined, but likely due to incoming air parcels enriched with emissions from agricultural burnings. Likewise, the daily CO2 cycle at ALTZ during the dry season shows evidence of a daily afternoon arrival of polluted air masses from the neighboring urban areas. This study lays the foundation of an upcoming expansion in the CO2 measurement sites and capabilities in the metropolitan area of Mexico City.

Friction velocity (u*) is an important velocity scale used in the study of engineering and geophysical flows. The widespread use of 2D sonic anemometers in modern meteorological stations makes the estimation of u* from just the horizontal components of the velocity a very attractive possibility. The presence of different wind regimes (such as sea breezes in or near coastal zones) causes the turbulent parameters to be dependent on the wind direction. Additionally, u* depends on atmospheric stability, whch makes the estimation of u* from 2D measurements very difficult. A simple expression is proposed, and then tested with data from six independent experiments located in coastal zones. The results show that it is possible to estimate friction velocity from 2D measurements using the turbulence intensity as a proxy for u*, reducing substantially the sensitivity to the wind direction or atmospheric stability, with small root mean squared errors (0.06 < RMSE < 0.097) and high correlation coefficients (0.77 < r2 < 0.95).

This study explored the nature of health risks in the population of three municipalities within the Metropolitan Area of the Valley of Mexico (MAVM) by means of an empirical analysis of health effects associated with air pollution and temperature variation. Based on the environmental justice theory, we asked whether, in unequal socioeconomic municipalities of the MAVM, the association between PM10 concentrations and mortality depends on socioeconomic disparities. We differ from previous studies that have established a relationship between PM10 and mortality based on a state-space model instead of the Poisson regression model. The state-space model allows estimating the size of the unobserved at-risk population, its hazard rate, the life expectancy of individuals in that population, and the effect of changes in environmental conditions on that life expectancy. Our results show a lower hazard rate in a wealthy municipality, as compared to a higher hazard rate in a poor one. The lower hazard rate of the wealthy municipality extends life expectancy and enhances the likelihood of inhabitants staying long-lasting within the population at risk, thus increasing the size of that population, as compared to the population at risk in the poor municipality, whose members show a lower life expectancy. Thus, the smaller the at-risk population, the sicker its average member and the smaller the impact on long-term mortality. Our study examines how regional health disparities could provide information for public health policy initiatives which might improve living conditions among different communities.

The city of Eskişehir is located in the Central Anatolia Region of Turkey, where harsh continental climatic characteristics are prevalent (i.e., cold winters and hot summers). In recent years, quality and quantity of studies on bioclimatic comfort have increased both all over the world and in Turkey. Outdoor bioclimatic comfort conditions are counted amongst the indicators of human quality of life in urban environments, together with other physical, social and economic features such as air quality, GDP, and possibilities of social activities. The calculated values representing bioclimatic comfort conditions have been used instead of individual mean values of some climatic elements, in order to provide an insight of the liveability of a city. The aim of the present research study is to determine: (1) hourly bioclimatic comfort conditions in the Eskişehir city center during sultry summer days, considering bioclimatic comfort values calculated according to 12-year data from urban, sub-urban and rural areas using the physiological equivalent temperature (PET) index and RayMan software for the calculation of solar radiation fluxes on individuals in the hottest five months of the year; (2) the spatial distribution of these comfort values in decades (10-day intervals) using Geographic Information Systems and raster maps, taking into consideration elevation and land use; and (3) which urban design and planning principles could be adopted to deal with adverse thermal comfort conditions triggered by the urban heat island (UHI) effect. The results of the study indicate that the poorest comfort conditions are provided in urban areas, while rural areas are more advantageous in terms of comfort conditions. New bioclimatic-sensitive urban design principles are taken into consideration to create more comfortable areas from the bioclimatic perspective (i.e., windier and less humid sites open to the prevalent wind direction and out of heat stress).

This study simulates an unusual extreme rainfall event that occurred in Salvador city, Bahia, Brazil, on December 9, 2017, which was named subtropical storm Guará and had precipitation of approximately 24 mm within less than 1 h. Numerical simulations were conducted using the Weather Research and Forecasting (WRF) model over three domains with horizontal resolutions of 9, 3, and 1 km. Different combinations of seven microphysics, three cumulus, and three planetary boundary layer schemes were evaluated based on their ability to simulate the hourly precipitation during this rainfall event. Statistical indices (MB = –0.69; RMSE = 4.11; MAGE = 1.74; r = 0.55; IOA = 0.66; FAC2 = 0.58) and time series plots showed that the most suitable configurations for this weather event were the Mellor-Yamada-Janjić, Grell-Freitas, and Lin formulations for the planetary boundary layer, cumulus, and microphysics schemes, respectively. The results were compared with the data measured at meteorological stations located in Salvador city. The WRF model simulated well the arrival and occurrence of this extreme weather event in a tropical and coastal region, considering that the region already has intense convective characteristics and is constantly influenced by sea breezes, which could interfere in the model results and compromise the performance of the simulations.

Biomass burning (BB) is a common activity in developing countries and has been identified as a serious air pollution threat. The present work for the first time evaluates the air quality of the largest town in the extensive Colombian savannas (250,000 km2), from measurements over three consecutive years (2017-2020). Although the air quality in Villavicencio is good in terms of PM10 and O3 for most of the year, pollution levels for both pollutants exceed the World Health Organization recommended limits during the dry season (February to April). The combination of the Orinoco low-level jet (OLLJ) and BB emissions from the Venezuelan and the Colombian savannas was identified as the main cause of poor air quality episodes during the dry season in this city. Organic carbon derived from reanalysis was identified as the main component of the high PM10 concentrations during the dry season. However, mineral dust and sea salt particles were also found to play an important role in the poor air quality observed in Villavicencio and likely along the Orinoco river basin region. Finally, between November and March, the OLLJ was found to be an efficient mechanism for the transport of air pollutants from the Atlantic Ocean and the savanna regions in the Orinoco River Basin in Venezuela and Colombia towards southern regions of Colombia, and in some cases even reaching Ecuador.

Time and intensity-specific very short-term forecasting or nowcasting is the biggest challenge faced by an aviation meteorologist. Ground-based microwave radiometer (MWR) has been used for nowcasting convective activity and it was established that there is a good comparison between thermodynamic parameters derived from MWR and GPS radiosonde observations, indicating that MWR observations can be used to develop techniques for nowcasting severe convective activity. In this study, efforts have been made to bring out the efficacy of MWR in nowcasting thunderstorms and fog. Firstly, the observations of MWR located at Palam, New Delhi, India have been compared with the nearest radiosonde data to ascertain the variation in respective profiles. Large differences were found in relative humidity (RH), whereas temperatures from MWR were found to be close to radiosonde observed temperature up to 3.5 km. Subsequently, the scatter plots and correlation coefficients of thermodynamic indices/parameters indicated that most of the parameters are either not correlated or have moderate correlation only for 12:00 UTC profiles. The superepoch technique of lagged composite for various thermodynamic indices/parameters to obtain a combined picture of all the thunderstorm and dense fog cases on the time series could not determine any pattern to predict thunderstorm and dense fog with lead time of 2-4 hours. MWR profile for a case of occurrence of thunderstorm was analyzed. No significant variation was observed in most of the indices (as calculated from MWR observed parameters) prior to the occurrence of thunderstorm. RH at freezing level and between 950 and 700 hPa levels were the only parameters, which increased four hours prior to the occurrence.

A split-window algorithm has been used in the Ilam dam watershed to determine the relationship between land surface temperature (LST) and types of land use. Landsat satellite images of the TM sensor for 1990, 1995, 2000, 2005 and 2010 and Landsat 8 (OLI Sensor) for 2015 and 2018 are used. After geometric and radiometric corrections of satellite images, land use maps are extracted by using the fuzzy ARTMAP method. An accuracy assessment showed that the highest value of the kappa coefficient was 94% with a total accuracy of 0.95 for 2015, and the lowest kappa coefficient value was 87% with a total accuracy of 0.9 for 1990. The high values of these coefficients indicate the acceptable accuracy of using Landsat’s remote sensing data for land use detection. The most important land use change is related to dense forest and sparse forest land uses, with decreases of 20.07 and 17.04%, respectively. The minimum LST measures in 1990, 2010, and 2018 in dense forest are 21.27, 30.55 and 33.82 ºC, respectively. The maximum LSTs for the sparse forest land use in 1990 and 2010 are 52.48 and 56.09, and 56.10 ºC for the dense forest land use in 2018. As a result, the average LST in agricultural lands was lower than in sparse forest and rangeland;, which is mainly due to the high moisture content and the greater evapotranspiration rate. Land use/land cover variations from 1990 to 2018 show that all land uses have experienced an increase in LST.

Air pollution in towns adjacent to and downwind of large cities can be similar or even higher than in the city itself. In the case of towns constituting the greater Bogotá area, with more than half a million inhabitants and strong industrial activity, little is known about the factors that affect their poor air quality. This work investigated the incremental excess of the composition and source contribution to PM2.5 in two sites near Bogotá (Soacha: 4º35’4.59” N, 74º13’11.62” W; and Mosquera: 4º42’9.75” N, 74º13’54.94” W), using the Chemical Mass Balance receptor model with organic molecular markers, and back trajectory analysis. Simultaneous sample collection was carried out for two-months. Organic matter was the major component of the PM2.5 mass (66 ± 14% and 61 ± 12%), while secondary inorganic ions (sulfate, nitrate, and ammonium) constituted 13 ± 8 % and 10 ± 2 %. The main anthropogenic sources contributing to PM2.5 at Soacha were wood combustion (23%), diesel vehicles (19%), and coal combustion at small facilities (11%). At Mosquera, they were gasoline vehicles (26%), diesel vehicles (19%), and coal combustion at small inefficient facilities (15%). The contribution of regional secondary organic aerosol to PM2.5 was significant (19% and 15%), arriving mostly from the Orinoco basin but higher in air masses arriving from the Amazon rainforest. The regional contribution to secondary inorganic aerosols was higher with winds from the Magdalena Valley. The methods presented in this manuscript will be useful in other megacities and large cities to better manage impacts of local and regional air pollution sources.

Itabira has in its territory the largest complex of opencast mining in the world, located close to residential areas of the city. The air quality monitoring network installed in the city is the main source of particulate matter (PM) emission data. However, these air quality stations only cover the areas near the mines and do not measure fine particulate matter (PM2.5). Thus, a first field campaign was carried out to characterize PM in the city and to compare high volume data from air quality stations with the dichotomous air sampler data. Results of trajectories’ cluster analysis showed a long-range transport of aerosols during the sampling days from northeast (84% of the trajectories), east-southeast (12%), and south-southwest (3%) directions. Regarding the meteorological conditions during the sampling days, negative correlations were seen between coarse particulate matter (PM10) from mostly air quality stations and all meteorological parameters (but temperature). Results of the X-ray fluorescence and principal component analyses showed that the main trace elements in the coarse (PM2.5-10) and fine modes (PM2.5) are iron and sulfur, associated with emissions from mining activities, air mass transport from regional iron and steelmaking industry activities, vehicle emissions, local and regional biomass burning, and natural biogenic emissions. This work is the first assessment of source apportionment done in the city. Comparisons with other studies, for some large metropolitan areas, showed that Itabira has comparable contributions of sulfur, iron and elements such as copper, selenium, chromium, nickel, vanadium and lead.

The occurrence of higher ground-level O3 concentrations on weekends rather than on weekdays, despite reduced anthropogenic activity in urban areas, is known as the O3 weekend effect (OWE). We present here an approach to analyse OWE spatio-temporal variations in urban areas, integrated by the trend, prediction and network representation. We used data from ten monitoring sites geographically distributed within the Mexico City Metropolitan Area (MCMA) recorded during 1994-2018. The OWE occurrence within the MCMA ranged typically between 40 and 60 % of the total weeks per year. The annual differences between weekday and weekend O3 peaks (magnitudes) showed were most significant on Sundays. Naive, Linear and Auto-regressive Integrated Moving Average models were tested for predicting the OWE annual occurrences and magnitudes. There was no single model that outperformed significantly for predicting OWE at all sites. The proposed concept of generalised OWE (GOWE) implies that at least half of the sites under study exhibited simultaneous OWE occurrence. GOWE is represented as a network and its integration with prediction models is useful to determine the OWE spread over the MCMA in the following years. The GOWE occurrence showed an increasing trend interpreted as the spread of VOC-limited conditions over most of the MCMA. Predicted data suggest that, with the current emission control policies, the GOWE will continue occurring. The integrated methodology presented provides valuable insight into the design of potential air quality control strategies.

Road transportation activities are major contributors of nitrogen oxides emissions to the air. The impact on the growth of NOx emission levels is found to be strongly correlated with the traffic intensities on highways. Various types of emission models performing emission assessment of traffic-related pollutants have been developed, but few of them were developed by using real-world measurements of NOx concentrations in ambient air. The most convenient sites to perform measurements in real-world conditions are road tunnels. This paper presents a comparison of HBEFA model NOx emission calculations and NOx emission measured in a short tunnel in the Czech Republic. Simultaneously, measured time-resolved NOx concentration and traffic activity counting were performed in the Zeleny most tunnel in the Czech Republic. The experimental work yielded reliable results of the mutual correlation of NOx level and traffic intensity in the tunnel section with statistical evidence. Emission factors from HBEFA emission model for road transport were applied and compared with the results from several measurement campaigns in the Czech Republic. It was found that calculated NOx emissions differed from measured NOx emissions due to the overestimation of light vehicles emissions and underestimation of high-duty vehicles emissions.

In studies of cloud seeding by ground-based generators, a dispersion analysis of the silver iodide (AgI) glaciogenic aerosol is a necessary tool to estimate if it reaches seeding heights. A study of the dispersion of AgI emitted by a network of generators with hypothetical locations in the eastern region of Cuba was developed using the WRF-Chem model. Two spatial distributions with different heights and distances between generators were analyzed. Two experiments were undertaken with emission rates of 10 and 30 g h–1, based on a sample of six days. The activation level was not reached for an emission rate of 10 g h–1, while for 30 g h–1 static seeding could occur but the area with seeding aerosol was not significant. The distribution in which generators were closer together turned out to be the one with smaller maximum concentrations and bigger areas occupied by the aerosol at a given level. Covered area and seeding aerosol concentrations increased for emission rates of 30 g h–1. In general, the plume follows the wind direction and its vertical rise is determined by the turbulent kinetic energy for the area where the generator is placed.