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ABSTRACT Analysis of the long-term time-series data on aerosol parameters at Delhi, an urban city in the western part of Indo-Gangetic Plain (IGP), brought out certain interesting findings. The time-series data are observed to be a complex function of different periodicities varying from intra-seasonal to inter-annual timescales. Detailed investigations of the periodicities in conjunction with the meteorological data demonstrated the prevalence of four periodicities such as intra-seasonal (periodicities of ∼2-3 months, significant at shorter wavelengths), semi-annual oscillation ( SAO, ∼6 months), annual oscillation ( AO, ∼12 months) and quasi-biennial oscillation ( QBO, ∼2 years) and quasi-triennial oscillation ( QTO, ∼3 years) at the measurement site in varying amplitudes. The AO and SAO are the dominant components in the aerosol optical depth ( AOD) as well as in the Angstrom parameters with a combined contribution of ∼40% to the climatological mean and are attributed to the changes in the prevailing meteorological conditions, which are conducive for either production, transport and/or size-transformation processes. Among the inter-annual variability in aerosol parameters, the most significant mode observed is the QTO and is found to be associated with the ENSO variability in the tropical pacific region. While the intra-seasonal fluctuations (∼2-3 months) observed in AOD (at shorter wavelengths) are associated with the eastward propagating Madden-Julian oscillations (MJO) in the lower troposphere, the biennial variability is related with variability in the meteorology of the upper and lower atmospheric regions. Periodicity analysis on aerosol parameters is useful to determine its predictability in the atmosphere. [ABSTRACT FROM AUTHOR]

The solar global ultraviolet (GUV) and broadband global (G) radiation flux obtained on a horizontal plane in Delhi, during April 2010 to March 2011 have been used to investigate the temporal variability of these radiations and their ratio, fraction of UV (FUV). For the first time the clearness index ( KT) has been estimated over Delhi and its variability during different months of the year and season has been studied in detail. The impact of atmospheric aerosols on KT has also been studied. It has been found that for every unit increase in aerosol optical depth (AOD) at 340 nm, KT decreases by 0.06. A strong anti-correlation with correlation coefficient − 0.75 is observed between AOD and KT. On the basis of our field experience and observations at Delhi it is found that for highly cloudy and overcast conditions 0⩽ KT⩽0.15, for partial cloudy or hazy conditions 0.15⩽ KT⩽0.21 and KT > 0.21 for clear sky conditions. In addition, during foggy days in winter we have found KT values lying in the range 0.12-0.18 at Delhi. The day-time daily-averaged fluxes GUV and G varied in the range 0.15-1.23 MJ m−2 and 3.36-27.02 MJ m−2, respectively. The GUV and G showed similar pattern during the year except for the wet season when the FUV increased possibly due to an increase in water vapour concentration. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The concentrations of PM10, PM2.5 and their water-soluble ionic species were determined for the samples collected during January to December, 2007 at New Delhi (28.63° N, 77.18° E), India. The annual mean PM10 and PM2.5 concentrations (± standard deviation) were about 219 (± 84) and 97 (±56) µgm−3 respectively, about twice the prescribed Indian National Ambient Air Quality Standards values. The monthly average ratio of PM2.5/PM10 varied between 0.18 (June) and 0.86 (February) with an annual mean of ∼0.48 (±0.2), suggesting the dominance of coarser in summer and fine size particles in winter. The difference between the concentrations of PM10 and PM2.5, is deemed as the contribution of the coarse fraction (PM10−2.5). The analyzed coarse fractions mainly composed of secondary inorganic aerosols species (16.0 µgm−3, 13.07%), mineral matter (12.32 µgm−3, 10.06%) and salt particles (4.92 µgm−3, 4.02%). PM2.5 are mainly made up of undetermined fractions (39.46 µgm−3, 40.9%), secondary inorganic aerosols (26.15 µgm−3, 27.1%), salt aerosols (22.48 µgm−3, 23.3%) and mineral matter (8.41 µgm−3, 8.7%). The black carbon aerosols concentrations measured at a nearby (∼300 m) location to aerosol sampling site, registered an annual mean of ∼14 (±12) µgm−3, which is significantly large compared to those observed at other locations in India. The source identifications are made for the ionic species in PM10 and PM2.5. The results are discussed by way of correlations and factor analyses. The significant correlations of Cl−, SO, K+, Na+, Ca2+, NO and Mg2+ with PM2.5 on one hand and Mg2+ with PM10 on the other suggest the dominance of anthropogenic and soil origin aerosols in Delhi. [ABSTRACT FROM AUTHOR]

Forests are an important natural resource and are instrumental in sustaining environmental sustainability. Burning biomass in forests results in greenhouse gas emissions, many of which are long-lived. Precise and consistent broad-scale monitoring of fire intensity is a valuable tool for analyzing climate and ecological changes related to fire. Remote sensing and geographic information systems provide an opportunity to improve current practice's accuracy and performance. Spectral indices techniques such as normalized burn ratio (NBR) have been used to identify burned areas utilizing satellite data, which aid in distinguishing burnt areas using their standard spectral responses. For this research, we created a split-panel web-based Google Earth Engine app for the geo-visualization of the region severely affected by forest fire using Sentinel 2 weekly composites. Then, we classified the burn severity in areas affected by forest fires in Wolgan Valley, New South Wales, Australia, and the surrounding area through Difference Normalized Burn Ratio (dNBR). The result revealed that the region's burnt area increased to 6731 sq. km in December. We also assessed the impact of long-term rainfall and land surface temperature (LST) trends over the study region to justify such incidents. We further estimated the effect of such incidents on air quality by analyzing the changes in the column number density of carbon monoxide and nitrogen oxides. The result showed a significant increase of about 272% for Carbon monoxide and 45% for nitrogen oxides. We conclude that, despite fieldwork constraints, the usage of different NBR and web-based application platforms may be highly useful for forest management to consider the propagation of fire regimes. [ABSTRACT FROM AUTHOR]

Measurements of direct UV irradiances (using a MICROTOPS II Sunphotometer) carried out from a high-latitude site, Antarctica are presented. The instantaneous irradiances at 305±0.9, 312±0.9 and 320±1.0 nm during a no-ozone-hole (13 December 2004) and an ozone-hole (4 October 2004) period have been observed to be about 0.031, 0.150 and 0.299 W m-2 and 0.010, 0.049 and 0.102 W m-2, respectively at local noontime. The observations of the direct UV irradiances at 305±0.9, 312±0.9 and 320±1.0 nm are compared with tropospheric ultraviolet visible (TUV) radiation transfer model calculations. The model estimate shows that, during the ozone-hole period, a loss of ozone of the order of 44% leads to an increase in irradiance of the order of 410%, 90% and 25% at 305±0.9, 312±0.9 and 320±1.0 nm, respectively. The relationship between change in UV irradiance due to a change in column ozone is obtained using a TUV model and irradiances thus estimated from this relationship are found to compare well with the observed irradiances. [ABSTRACT FROM AUTHOR]

Abstract: Indo-Gangetic (IG) alluvial plains, one of the largest river basins in the world, suffers from the long range transport of mineral dust from the western arid and desert regions of Africa, Arabia and Rajasthan during the summer (pre-monsoon season, April–June). These dust storms influence the aerosol optical depth (AOD) across the IG plains. The Kanpur AERONET (Aerosol Robotic Network) station and Moderate Resolution Imaging Spectro-radiometer (MODIS) data show pronounced effect on the aerosol optical properties and aerosol size distribution during major dust storm events over the IG plains that have significant effect on the aerosol radiative forcing (ARF). The multi-band AOD, from AERONET and MODIS, show contrasting changes in wavelength dependency over dust affected regions. A time collocated (±30min) validation of AERONET AOD with MODIS Terra (level 2 swath product) over Kanpur, at a common wavelength of 550nm for the period 2001–2005 show moderate correlation (R 2∼0.6) during the summer season. The average surface forcing is found to change by −23Wm−2 during dust events and the top of the atmosphere (TOA) forcing change by −11Wm−2 as compared to the non-dusty clear-sky days. A strong correlation is found between AOD at 500nm and the ARF. At surface, the correlation coefficient between AOD and ARF is found to be high (R 2=0.925) and is found to be moderate (R 2=0.628) at the TOA. The slope of the regression line gives the aerosol forcing efficiency at 500nm of about −46±2.6Wm−2 and −17±2.5Wm−2 at the surface and the TOA, respectively. The ARF is found to increase with the advance of the dry season in conjunction with the gradual rise in AOD (at 500nm) from April (0.4–0.5) to June (0.6–0.7) over the IG plains. [Copyright &y& Elsevier]

The flash flood-induced erosion is the primary contributor to soil loss within the Indian Himalayan Region (IHR). This phenomenon is exacerbated by a confluence of factors, including extreme precipitation events, undulating topographical features, and suboptimal soil and water conservation practices. Over the past few decades, several flash flood events have led to the significant degradation of pedosphere strata, which in turn has caused landslides along with fluvial sedimentation in the IHR. Researchers have advocated morphometric, hydrologic, and semi-empirical methods for assessing flash flood-induced soil erosion in hilly watersheds. This study critically examines these methods and their applicability in the Alaknanda River basin of the Indian Himalayan Region. The entire basin is delineated into 12 sub-watersheds, and 13 morphometric parameters are analyzed for each sub-watershed. Thereafter, the ranking of sub-watersheds vulnerability is assigned using the Principal Component Analysis (PCA), compounding method (CM), Geomorphological Instantaneous Unit Hydrograph (GIUH), and Revised Universal Soil Loss Equations (RUSLE) approaches. While the CM method uses all 13 parameters, the PCA approach suggests that the first four principal components are the most important ones, accounting for approximately 89.7% of the total variance observed within the dataset. The GIUH approach highlights the hydrological response of the catchment, incorporating dynamic velocity and instantaneous peak magnifying the flash flood susceptibility, lag time, and the time to peak for each sub-watershed. The RUSLE approach incorporates mathematical equations for estimating annual soil loss utilizing rainfall-runoff erosivity, soil erodibility, topographic, cover management, and supporting practice factors. The variations in vulnerability rankings across various methods indicate that each method captures distinct aspects of the sub-watersheds. The decision-maker can use the weighted average to assign the overall vulnerability to each sub-watershed, aggregating the values from various methods. This study considers an equal weight to the morphometric, hydrological GIUH, and semi-empirical RUSLE techniques to assess the integrated ranking of various sub-watersheds. Vulnerability to flash flood-induced landslides in various sub-watersheds is categorized into three classes. Category I (high-priority) necessitates immediate erosion control measures and slope stabilization. Category II (moderate attention), where rainwater harvesting and sustainable agricultural practices are beneficial. Category III (regular monitoring) suggests periodic community-led soil assessments and afforestation. Sub-watersheds WS11, WS8, WS5, and WS12 are identified under category I, WS7, WS4, WS9, and WS6 under category II, and WS1, WS3, WS2, and WS10 under category III. The occurrence of landslides and flash-flood events and field observations validates the prioritization of sub-watersheds, indicating the need for targeted interventions and regular monitoring activities to mitigate environmental risks and safeguard surrounding ecosystems and communities., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)