Indo-Gangetic Plain Region Research Articles

Hotspot analysis and long-term trends of absorbing aerosol index from dust emissions measured by the Ozone Monitoring Instrument at different urban locations in India during 2005–2018

The dust storm is a natural hazard and knowledge of hotspots of dust emission is important to improve forecasting the dust events by numerical models of climate and air quality. The absorbing aerosol index (AAI) observations derived from the Ozone Monitoring Instrument (OMI) sensor are analyzed over India covering the period from 2005 to 2018. In this manuscript, the hotspot analysis of AAI was conducted using the spatial autocorrelation technique for different seasons. The results showed significant spatial and temporal variability in the observed AAI. During pre-monsoon, the hotspot region is widely distributed, though with noticed spatially varying intensities, from the Thar Desert to West Bengal through the Indo Gangetic Plain (IGP) region. It is revealed from the back trajectory analysis that the airmasses were originated from the arid desert regions located in the West of India transporting the dust particles during the pre-monsoon over the IGP regions. Further, the trend analysis of AAI during the pre-monsoon over selected metropolitan in India was done using the Mann–Kendall (MK) test and Sen's robust slope estimator. The results showed a significant increasing (0.02 yr−1) and decreasing (−0.01 yr−1) trend in AAI at Patna and Hyderabad, respectively, while it is noticed stable or no trend at other cities. MERRA-2 Dust aerosol optical thickness was found to be very well correlated with AAI and shows decreasing and increasing trends at Nagpur (0.0005 yr−1) and Jaisalmer (0.004 yr−1), respectively. A negative correlation is observed between rainfall and AAI, indicating the reduction of AAI with increasing rainfall.

Inter-Annual and Seasonal Variability in Ambient Ultraviolet-B Radiation Level at a Tropical Region of Indo-Gangetic Plain

This study evaluated the annual, seasonal, and diurnal variations in the ambient UV-B levels at a tropical region of the Indo-Gangetic plain during 2016 – 2018. Prominent seasonal variations in ambient Ultraviolet-B (UV-B) levels were recorded. Daytime cumulative UV-B varied from 16.75-37.45 (2016), 13.08- 35.89 (2017) and 14.76-34.5 (2018) during summer; from 24.02-3.65 (2016), 18.32-3.11 (2017) and 11.09-2.09 (2018) during winter and 25.56 – 41.17 (2016), 20.1 – 39.21 (2017) and 14.82 – 37.18 (2018) during rainy season. The ambient UV-B level was dependent on numerous meteorological variables (cloud cover, relative humidity, rainfall, and sunshine hours), astronomical factors (Solar Zenith Angle), and pollutants (like tropospheric ozone, sulphur dioxide, nitrogen dioxide, and aerosols). Monthly average UV-B levels positively varied with sunshine hours and PAR and inversely varied with cloud cover. This study suggests that the region is exposed to highly dynamic UV-B levels, which could be a potent threat to plants specially grown during summer-rainy seasons. The study could be further expanded for the entire region using various mathematical tools.

Benzene and Toluene from Stubble Burning and Their Implications for Ozone Chemistry and Human Health in the Indo-Gangetic Plain Region

Benzene and Toluene from Stubble Burning and Their Implications for Ozone Chemistry and Human Health in the Indo-Gangetic Plain Region

Characteristic dissimilarities during high aerosol loading days between western and eastern Indo-Gangetic Plain

This study investigates the long-term (2003–2019) variations of high aerosol loading days and their radiative impacts over the western Indo-Gangetic Plain (IGP) and eastern IGP during pre-monsoon season (March-April-May-June). The Aerosol Optical Depth (AOD) climatology from MODIS (Terra and Aqua) and MERRA-2 reanalysis shows high aerosol burden across the IGP region during the pre-monsoon season. The high aerosol loading days are identified based on a standardized AOD anomaly approach, from MODIS and MERRA-2. The frequency of high aerosol loading days over the western IGP is roughly twice that of the total number of high aerosol loading days over the eastern IGP. The area-averaged percentage differences in AOD between high aerosol loading days and normal days over western IGP is always higher, about 6–8%, than eastern IGP from Terra, Aqua and MERRA-2. The natural (mainly dust) and anthropogenic aerosols (particularly sulfate, black carbon and organic carbon) are majorly contributed to total AOD over western IGP and eastern IGP. Furthermore, the MERRA-2 and ERA5 composite surface and 850 hPa wind anomalies show that strong westerly winds dominate, transporting dust aerosols from arid regions to the western IGP. On the other hand, weak prevailing winds and background pre-monsoonal cyclonic circulations over eastern IGP favor the accumulation of regionally emitted aerosols. During high aerosol loading days, the decrease in ventilation coefficient indicates the high aerosol burden (less dispersion) over both the regions, leading to the deterioration of air quality. The enhanced aerosol loading induced potential atmospheric radiative forcing (19.78 Wm-2 over western IGP and 20.77 Wm-2 over eastern IGP) during high aerosol loading days compared to normal days (11.12 Wm-2 and 12.9 Wm-2).

Evaluating temperature thresholds and optimizing sowing dates of wheat in Bihar


 Studies on wheat-weather relationship were carried out at Pusa (25.98 oN, 85.67 oE, 52 m), Bihar situated in middle Gangetic plains of India, with three popular wheat cultivars viz. RW 3711, HD 2824 and HD273, grown under five fixed dates of sowing viz. 15 November, 25 November, 5 December, 15 December and 25 December, for five consecutive rabi seasons from 2011-12 to 2015-16. Thresholds of maximum temperature (Tmax), minimum temperature (Tmin) and bright sunshine hours (BSH), associated with higher productivity, occurring at different phenophases, were determined. Results revealed that temperature played a crucial role in achieving higher grain yield of wheat. Both Tmax and Tmin during flowering to milking and flowering to maturity phases increased with delayed sowing dates beyond 25 November with consequent reductions in grain yield. During 50 % flowering to milk stage, Tmax and Tmin above 24.6 oC and 11.6 oC, respectively, reduced grain yield below 4000 kg ha-1; significant reduction in grain yield was also noted beyond maximum temperature of 26.9 oC. During flowering to milk and flowering to maturity phases, Tmax and Tmin exhibited highly significant negative correlation with grain yield, indicating higher temperatures causing lower grain yield. With delayed sowing, sensitive phases of the crop experienced higher air temperatures which led to reduction in grain yield. An increase of Tmax from 29.2 to 32.1 oC during flowering to maturity phases reduced the wheat productivity drastically in this region of Indo-Gangetic plains. Grain yield declined by 399 kg ha-1 per 1 oC rise in Tmax during 50 % flowering to maturity stage. Considering grain yield vis-à-vis temperature regimes during flowering to maturity stage, the most important recommendation for the farmers of the region would be to finish wheat sowing before 25 November in order to enable them to escape terminal heat stress in wheat and thereby realizing higher grain yield. The anthesis-time management by manipulating sowing dates could be a realistic adaptation strategy for attaining optimum grain yield under changing climate scenario.

Probabilistic Assessment of Extreme Heat Stress on Indian Wheat Yields Under Climate Change

AbstractThe wheat belt along the Indo‐Gangetic Plains (IGP) in India is an emergent hotspot of climate change‐driven crop loss threatening local food security. Using statistical Generalized Linear Models, observed temperature and wheat production data, we show an increase in magnitude, frequency and areal extent of heat stress episodes in the IGP region during 1967–2018. Such episodes comprise of temperatures exceeding a senescence‐inducing threshold. Further, using a copula‐based multivariate framework, we probabilistically assess wheat production conditioned on heat stress indicators, both in the historical period and also in the Coupled Model Intercomparison Project (CMIP6) future projections. Probabilistic estimates of below‐average wheat production under scenario‐averaged heat stress conditions are expected to rise by 8%–27% under the SSP5‐8.5 scenario, with Punjab showing the largest increase. Quantitative links between heat stress indicators and loss of crop yield highlight increased agricultural vulnerability in India under climate change.

Assessment of physiological, biochemical and yield responses of wheat plants under natural saline and non-saline field conditions.

Soil salinity is a major threat to crop productivity all over the world including the Indo-Gangetic plain (IGP) region of India. Therefore, a field study was conducted for two consecutive years in wheat growing areas in IGP affected by salinity. Plants grown at a saline site (Salempur, SLM) and a non-saline site (Rajatalab, RJT), were analysed for selected biochemical, physiological and yield traits. Results showed that photosynthetic rate was not significantly affected, but transpiration rate and stomatal conductance declined at saline compared to non-saline site. Photosynthetic pigments increased during vegetative growth period, but decreased during reproductive stage at SLM site, while anthocyanin showed an opposite trend. Membrane damage, solute leakage, H2O2 and ·O2 - productions were intensified at saline site, SLM. Accumulation of osmolytes and antioxidants occurred in plants at saline compared to non-saline sites. K/Na and Ca/Na ratios in plants at SLM were reduced significantly compared to non-saline site, RJT. Biomass and yield also declined at SLM compared to RJT. Principle component and path analyses on the measured parameters clearly showed that defense strategies adopted by plants helped to maintain the photosynthetic rate but biomass and yield of wheat got compromised under high salinity.

Wet deposition of total dissolved nitrogen in Indo-Gangetic Plain (India)

Very limited information on the magnitude and environmental impacts of both inorganic and organic forms of nitrogen (N) wet deposition is available in India. Molar concentrations of inorganic (NH4+ and NO3-) and organic N in rainwater were monitored at three different land use sites in Indo-Gangetic Plain (IGP) during the monsoon period (June-September) of 2017. It has been observed that dissolved organic N (DON) contributed significantly to the total dissolved N (TDN) ranging from 5 to 60%. Dissolved inorganic N (DIN = NH4+ + NO3-) concentration was recorded as high as 221.0 μmol L-1 at urban site to as low as 65.9 μmol L-1 at the rural site. A similar pattern was also observed for DON. NH4+ contribution to TDN had the order urban megacity (65%) > urban (70%) > rural (75%). Agriculture and animal husbandry are the primary sources of NH4+ emissions in the rural site. However, NO3- has shown a contrasting trend at these sites (25%, 15%, and 8%, respectively). Wet deposition fluxes of atmospheric TDN were observed to be higher at urban sites. This can be attributed to a variety of local sources such as vehicular emission, microbial emissions, biomass burning, human excreta due to higher population density, and transportation from surrounding areas, as observed from concentration weighted trajectories (CWT) model and cluster analysis. Upwind region of IGP has experienced major influence of air mass transported from agriculturally rich northwest part of India. However, both the downwind sites have experienced by-and-large the influence of south-westerly air masses originated over the Arabian Sea. This study has found that the DON contributes significantly to TDN, and therefore, its inclusion for nitrogen budget assessment in South Asia is emphasized.

Characterization and sources of fine carbonaceous aerosol in winter over a megacity on Indo-Gangetic plain

The characteristics and sources of carbonaceous aerosol (CA) was studied during winter in the lower atmosphere of Kolkata, a megacity situated in the lower Indo-Gangetic plain region. The city air was laden with typically high EC (15.4 ± 9.4 μg/m3) and OC (32.2 ± 17.8 μg/m3) in winter. NASA's MERRA-2 reanalysis aerosol products underestimated PM2.5, EC, and OC with a mean bias of 41.0 ± 56.8 μg/m3, 10.1 ± 9.3 μg/m3, and 10.8 ± 18.2 μg/m3, respectively. The EC/BC ratio for the atmosphere of Kolkata was estimated to be 1.03 ± 0.50. Levoglucosan was estimated in PM2.5 as a biomass burning tracer (266.9 ± 189.5 ng/m3). Source apportionment of CA using the tracer method indicated 43% of CA (19% of total PM2.5) was of secondary origin. 49% of total CA (21% of PM2.5) was from fossil fuel combustion, consisting of 23% of EC and 26% OC. Biomass burning contributed to 8% of CA and 3% of PM2.5. The diel trend of EC indicated equivalent primary emission throughout the day except being significantly high in the morning time during rush hours of traffic and increased residential combustion. Despite lower dispersion, OC formation was much higher during sunlight, indicating extensive secondary organic aerosol formation.

Understanding seasonal variation in ambient air quality and its relationship with crop residue burning activities in an agrarian state of India.

In India, Indo-Gangetic Plains (IGP) is becoming the hotspot of air pollution due to increasing anthropogenic activities such as rapid industrial growth, infrastructure development, transportation activities, and seasonal practice of crop residue burning. In the current study, seasonal variation in ambient air quality for 14 parameters, i.e., particulate matter (PM), trace gases, and volatile organic compounds (VOCs), along with meteorological parameters, was studied in 21 districts of the Haryana state for year 2019, situated in IGP. To analyze spatial variation of pollutants, ambient air quality data of 23 continuous ambient air quality monitoring stations were divided into three zones based on ecology and cropping pattern. All the zones showed annual mean PM10 and PM2.5 concentrations much higher than national ambient air quality standards. Annual mean PM10 concentration (±standard deviation) in Zones-1, 2, and 3 was 156±86, 174±93, and 143±74 μg m-3, whereas for PM2.5 was 71±44, 85±54, and 78±47 μg m-3. The results showed a considerable seasonal variation in the concentration of all pollutants. Most of the pollutants peak in the post-monsoon season, followed by winters in which crop residue burning predominates in many parts of the Haryana. PM10 concentrations increased by 65-112% and PM2.5 concentrations increased by 131-147% in the post-monsoon season compared to monsoons. The post-monsoon season showed the highest concentration of PM10, NO, and toluene (Zone-1); and PM2.5, NH3, CO, and benzene (Zone-2); whereas in winters, SO2 (Zone-1); ethylbenzene, m,p-xylene, and xylene (Zone-2); and NO2 and NOx (Zone-3) showed the maximum pollution levels. The O3 concentration was highest in the pre-monsoon season (Zone-1). The satellite-based fire counts and PCA results show a significant influence of crop residue burning in the post-monsoon season and solid biomass burning in winters on Haryana's air quality. The study could help to understand seasonal variation in ambient air quality and the influence of factors such as crop residue burning in the IGP region, which could help to formulate season-specific control measures to improve regional air quality.

Nitrogenous and carbonaceous aerosols in PM2.5 and TSP during pre-monsoon: Characteristics and sources in the highly polluted mountain valley

This study reports for the first time a comprehensive analysis of nitrogenous and carbonaceous aerosols in simultaneously collected PM2.5 and TSP during pre-monsoon (March–May 2018) from a highly polluted urban Kathmandu Valley (KV) of the Himalayan foothills. The mean mass concentration of PM2.5 (129.8 µg/m3) was only ~25% of TSP mass (558.7 µg/ m3) indicating the dominance of coarser mode aerosols. However, the mean concentration as well as fractional contributions of water-soluble total nitrogen (WSTN) and carbonaceous species reveal their predominance in find-mode aerosols. The mean mass concentration of WSTN was 17.43±4.70 µg/m3 (14%) in PM2.5 and 24.64±8.07 µg/m3 (5%) in TSP. Moreover, the fractional contribution of total carbonaceous aerosols (TCA) is much higher in PM2.5 (~34%) than that in TSP (~20%). The relatively low OC/EC ratio in PM2.5 (3.03 ± 1.47) and TSP (4.64 ± 1.73) suggests fossil fuel combustion as the major sources of carbonaceous aerosols with contributions from secondary organic aerosols. Five-day air mass back trajectories simulated with the HYSPLIT model, together with MODIS fire counts indicate the influence of local emissions as well as transported pollutants from the Indo-Gangetic Plain region to the south of the Himalayan foothills. Principal component analysis (PCA) also suggests a mixed contribution from other local anthropogenic, biomass burning, and crustal sources. Our results highlight that it is necessary to control local emissions as well as regional transport while designing mitigation measures to reduce the KV's air pollution.

State of air pollutants and related health risk over Haryana India as viewed from satellite platform in COVID-19 lockdown scenario

COVID-19 driven lockdown has affected air quality worldwide. Changes in air pollutants concentration, Air Quality Index (AQI), and associated Excess Health Risk (ER%) were assessed using satellite data of before (2019), and during (2020) COVID-19 periods in the industrially, agriculturally developed and highly populated area of Haryana in the northern region of Indo-Gangetic Plains. Parameters such as Aerosol Optical Depth (AOD), Particulate matters (PM), Sulphur Di-Oxide (SO2), Nitrogen Di-Oxide (NO2), Carbon Mono-oxide (CO), and Methane (CH4) were derived using satellite data and validated using ground-based observations (n = 23). The coefficient of correlation (r) 0.91, 0.90, 0.95, 0.73, 0.81 and 0.80 were established with AOD, PM2.5, PM10, SO2, NO2 and CO, respectively. Significant reduction (p < 0.005) in the concentration of air pollutants, viz. 38% in AOD, 55% in PM2.5, 61% in PM10, 31% in SO2, 10% in NO2, 5% in CO and 1% in CH4 were observed during lockdown. Significant (p < 0.00) improvement in air quality was observed due to a 44% reduction in pollution level, which led to the reduction in ER% by 71%, which is quite significant. AQI and ER% from satellite and ground showed a high r2 i.e. 0.88 and 0.99 respectively, suggesting the potential application of satellite data for periodic AQI and ER% assessment.

Atmospheric particle-bound mercury in the northern Indo-Gangetic Plain region: Insights into sources from mercury isotope analysis and influencing factors

Lumbini is a world heritage site located in the southern plains region of Nepal, and is regarded as a potential site for evaluating transboundary air pollution due to its proximity to the border with India. In this study, 82 aerosol samples were collected between April 2013 and July 2014 to investigate the levels of particulate-bound mercury (PBM) and the corresponding seasonality, sources, and influencing factors. The PBM concentration in total suspended particulate (TSP) matter ranged from 6.8 pg m−3 to 351.7 pg m−3 (mean of 99.7 ± 92.6 pg m−3), which exceeded the ranges reported for remote and rural sites worldwide. The Hg content (PBM/TSP) ranged from 68.2 ng g−1 to 1744.8 ng g−1 (mean of 446.9 ± 312.7 ng g−1), indicating anthropogenic enrichment. The PBM levels were higher in the dry season (i.e., winter and the pre-monsoon period) than in the wet season (i.e., the monsoon period). In addition, the δ202Hg signature indicated that waste/coal burning and traffic were the major sources of Hg in Lumbini during the pre-monsoon period. Meanwhile, precipitation occurring during photochemical processes in the atmosphere may have been responsible for the observed Δ199Hg values in the aerosol samples obtained during the monsoon period. The PBM concentration was influenced mostly by the resuspension of polluted dust during dry periods and crop residue burning during the post-monsoon period. The estimated PBM deposition flux at Lumbini was 15.7 μg m−2 yr−1. This study provides a reference dataset of atmospheric PBM over a year, which can be useful for understanding the geochemical cycling of Hg in this region of limited data.

Measurement report: An assessment of the impact of a nationwide lockdown on air pollution – a remote sensing perspective over India

Abstract. The nationwide lockdown was imposed over India from 25 March to 31 May 2020 with varied relaxations from phase I to phase IV to contain the spread of COVID-19. Thus, emissions from industrial and transport sectors were halted during lockdown (LD), which has resulted in a significant reduction of anthropogenic pollutants. The first two lockdown phases were strictly implemented (phase I and phase II) and hence were considered to be total lockdown (TLD) in this study. Satellite-based tropospheric columnar nitrogen dioxide (TCN) from the years 2015 to 2020, tropospheric columnar carbon monoxide (TCC) during 2019/20, and aerosol optical depth (AOD550) from the years 2014 to 2020 during phase I and phase II LD and pre-LD periods were investigated with observations from Aura OMI, Sentinel-5P TROPOMI, and Aqua and Terra MODIS. To quantify lockdown-induced changes in TCN, TCC, and AOD550, detailed statistical analysis was performed on de-trended data using the Student paired statistical t test. Results indicate that mean TCN levels over India showed a dip of 18 % compared to the previous year and also against the 5-year mean TCN levels during the phase I lockdown, which was found to be statistically significant (p value &lt; 0.05) against the respective period. Furthermore, drastic changes in TCN levels were observed over hotspots, namely eastern region and urban cities. For example, there was a sharp decrease of 62 % and 54 % in TCN levels compared to 2019 and against 5-year mean TCN levels over New Delhi with a p value of 0.0002 (which is statistically significant) during total LD. The TCC levels were high in the northeast (NE) region during the phase I LD period, which is mainly attributed to the active fire counts in this region. However, lower TCC levels are observed in the same region due to the diminished fire counts during phase II. Further, AOD550 is reduced over the country by ∼ 16 % (Aqua and Terra) from the 6-year (2014–2019) mean AOD550 levels, with a significant reduction (Aqua MODIS 28 %) observed over the Indo-Gangetic Plain (IGP) region with a p value of ≪ 0.05. However, an increase in AOD550 levels (25 % for Terra MODIS, 15 % for Aqua MODIS) was also observed over central India during LD compared to the preceding year and found significant with a p value of 0.03. This study also reports the rate of change of TCN levels and AOD550 along with statistical metrics during the LD period.

Isotope and hydrochemical systematics of groundwater from a multi-tiered aquifer in the central parts of Indo-Gangetic Plains, India – Implications for groundwater sustainability and security

The Indo-Gangetic multi-aquifer system provides water supplies to the most populous regions of the Indian subcontinent, however precise knowledge on the sources and dynamics of groundwater is still missing. Environmental isotopes (2H, 18O, 13C, 3H and 14C) and hydrochemical modeling tools were used in this study in the multi-tiered aquifers underlying the Middle Gangetic Plains (MGP) to investigate the source of recharge, aquifer dynamics and inter-connectivity among aquifers. Within a depth span of 300 m, three aquifers, with contrasting recharge sources and dynamics, were delineated in this Sone-Ganga-Punpun interfluve region, with limited cross-aquifer hydraulic interconnections. The chemistry evolves from Ca-HCO3 to Na-Ca-HCO3 in the shallow semiconfined Aquifer-I with a mean transit time of 20–23 years. The dominant recharge to Aquifer-I is from the river inflows and rainwater percolation through paleochannels. The semi-confined to confined Aquifer-II holds fresh quality groundwater with mixed water facies (Mg/Ca-Na-HCO3). The modeled age of Aquifer-II groundwater is found to be 205–520 years, which is supported by presence of negligible tritium and minor variations in stable isotopes. Outcrop regions of Aquifer-II sediments in the marginal alluvial areas and deep-seated paleochannels in the southwestern part are the potential zones for Aquifer-II recharge. A deep confined Aquifer-III with fresh quality of groundwater is identified below 220 m. This aquifer is characterized by old age (~3.5 to 4.7 ka BP) and enriched δ18O (−5.7‰). These results along with the existing paleoclimate records of this region infer that Aquifer-III is recharged during an arid climate. The marginal alluvial plains are the probable recharge zones for Aquifer-III. This study helped in conceptualizing the groundwater flow paths in multi-tiered aquifers of MGP. The knowledge and understanding would extend crucial inputs for the sustainable development of deep aquifers not only in the MGP but also in other regions of Indo-Gangetic Plains.

Wintertime direct radiative effects due to black carbon (BC) over the Indo-Gangetic Plain as modelled with new BC emission inventories in CHIMERE

Abstract. To reduce the uncertainty in climatic impacts induced by black carbon (BC) from global and regional aerosol–climate model simulations, it is a foremost requirement to improve the prediction of modelled BC distribution, specifically over the regions where the atmosphere is loaded with a large amount of BC, e.g. the Indo-Gangetic Plain (IGP) in the Indian subcontinent. Here we examine the wintertime direct radiative perturbation due to BC with an efficiently modelled BC distribution over the IGP in a high-resolution (0.1∘ × 0.1∘) chemical transport model, CHIMERE, implementing new BC emission inventories. The model efficiency in simulating the observed BC distribution was assessed by executing five simulations: Constrained and bottomup (bottomup includes Smog, Cmip, Edgar, and Pku). These simulations respectively implement the recently estimated India-based observationally constrained BC emissions (Constrainedemiss) and the latest bottom-up BC emissions (India-based: Smog-India; global: Coupled Model Intercomparison Project phase 6 – CMIP6, Emission Database for Global Atmospheric Research-V4 – EDGAR-V4, and Peking University BC Inventory – PKU). The mean BC emission flux from the five BC emission inventory databases was found to be considerably high (450–1000 kg km−2 yr−1) over most of the IGP, with this being the highest (&gt; 2500 kg km−2 yr−1) over megacities (Kolkata and Delhi). A low estimated value of the normalised mean bias (NMB) and root mean square error (RMSE) from the Constrained estimated BC concentration (NMB: &lt; 17 %) and aerosol optical depth due to BC (BC-AOD) (NMB: 11 %) indicated that simulations with Constrainedemiss BC emissions in CHIMERE could simulate the distribution of BC pollution over the IGP more efficiently than with bottom-up emissions. The high BC pollution covering the IGP region comprised a wintertime all-day (daytime) mean BC concentration and BC-AOD respectively in the range 14–25 µg m−3 (6–8 µg m−3) and 0.04–0.08 from the Constrained simulation. The simulated BC concentration and BC-AOD were inferred to be primarily sensitive to the change in BC emission strength over most of the IGP (including the megacity of Kolkata), but also to the transport of BC aerosols over megacity Delhi. Five main hotspot locations were identified in and around Delhi (northern IGP), Prayagraj–Allahabad–Varanasi (central IGP), Patna–Palamu (mideastern IGP), and Kolkata (eastern IGP). The wintertime direct radiative perturbation due to BC aerosols from the Constrained simulation estimated the atmospheric radiative warming (+30 to +50 W m−2) to be about 50 %–70 % larger than the surface cooling. A widespread enhancement in atmospheric radiative warming due to BC by 2–3 times and a reduction in surface cooling by 10 %–20 %, with net warming at the top of the atmosphere (TOA) of 10–15 W m−2, were noticed compared to the atmosphere without BC, for which a net cooling at the TOA was exhibited. These perturbations were the strongest around megacities (Kolkata and Delhi), extended to the eastern coast, and were inferred to be 30 %–50% lower from the bottomup than the Constrained simulation.

Sustainable alternative crop rotations to the irrigated rice-wheat cropping system of Indo-Gangetic plains of India

ABSTRACT In recent years, the sustainability of the rice-wheat cropping system in Indo-Gangetic Plains is facing many problems in various fronts viz., agricultural, ecological, environmental and economical. Therefore, to ensure long-term sustainability, the rice-wheat cropping system needs to be diversified. The present study was conducted to identify an alternative cropping system for Indo-Gangetic Plains region of India by diversifying and intensifying the current rice-wheat cropping system. Ten treatments (rice-wheat = control, rice-wheat-green gram, rice-potato-green gram, rice-wheat-cowpea fodder, rice-potato-cowpea fodder, rice-berseem fodder-maize fodder, rice-berseem fodder-cowpea fodder, rice-mustard-sudan grass fodder, rice-mustard-cowpea fodder and rice-cabbage-cowpea fodder) were compared consecutively two years in randomized block design with three replications. Diversification of rice-wheat cropping system with rice-potato-green gram resulted in increase in system productivity (142.35%), gross returns (99.57%), net returns (130.34%), profitability (130.96%), relative production efficiency (142.53%), relative economic efficiency (130.79%) and labour employment (55.73%). The inclusion of legume crops in cropping sequences was found better in improving the soil quality parameters. Our results revealed the significance of diversification and intensification of rice-wheat cropping system under irrigated ecosystem of IGP as it enhanced system productivity, profitability and soil health.

Aerosol characteristics from earth observation systems: A comprehensive investigation over South Asia (2000–2019)

The present study summarizes two decades (2000–2019) of climatology and trends in aerosol loading and optical properties using a high spatial resolution data obtained from NASA's MODIS MAIAC and MISR aerosol products supplemented by moderate resolution aerosol data from OMI sensor over South Asia (SA). MISR AOD showed good agreement against AERONET AOD with 68.68% of the retrievals falling within the expected error and high Pearson's correlation coefficient (R = 0.83). The 20 years geometric mean of MAIAC and MISR AOD revealed higher loading of aerosols over the Indo-Gangetic Plain (IGP) and Eastern coast of India by 30% to 44% compared to the mean AOD over the entire SA. The highest mean AOD under cloud-free conditions was noted during monsoon season, followed by pre-monsoon, post-monsoon, and winter. The high contribution of coarse-mode AOD (cAOD) mainly from natural aerosol emission and small-mode AOD (sAOD) from local anthropogenic emissions are the main driver to high AOD in monsoon and pre-monsoon seasons. Besides, the presence of high humidity during the monsoon season favors the hygroscopic growth of the particles and leads to higher AOD values over SA. The high spatial resolutions of MODIS/MAIAC and MISR aerosol products enabled the identification of previously unobserved aerosol hotspots over Bihar, West Bengal, and the eastern Indian coastal state of Odisha, which is mainly dominated by small aerosol particles. The contributions of smaller aerosol particles to the total aerosol loading were found to be higher during post-monsoon and winter over most states in India, Nepal, and Bangladesh. In contrast, the contribution of coarser particles was higher over Pakistan during pre-monsoon and monsoon seasons. Smaller particles were predominantly retrieved over the Indian states dominated by mining industries, including Jharkhand and Odisha. A typical dominance of absorbing carbonaceous aerosols was also noted over the northwestern region of IGP during post-monsoon, which otherwise was mainly affected by mixed dust aerosols and carbonaceous aerosols in pre-monsoon and monsoon seasons. A statistically significant positive temporal trend in AOD was observed for the whole study period, over most of the SA region, which was influenced by the increase in small particles over India and Bangladesh. Urban/industrial weakly absorbing aerosols were found to be the main contributor to a similarly positive trend over Central India and East coast Indian states. Overall, recent advancements in high spatial resolution satellite-based aerosol optical properties showed good potential to identify the aerosol hotspots and constrain aerosol types across a highly polluted SA region.

Effect of COVID-19 shutdown on aerosol direct radiative forcing over the Indo-Gangetic Plain outflow region of the Bay of Bengal

The Indo Gangetic Plain (IGP), one of the most densely populated regions of the world, is a global hotspot of anthropogenic aerosol emissions. In the pre-monsoon season (March–May), the strong westerlies carry transported dust aerosols along with anthropogenic aerosols onto the Bay of Bengal (BoB). The outflow from IGP modulates the aerosol loading and the aerosol direct radiative forcing (ADRF) over the BoB. The quantification of the anthropogenic aerosol impact on the radiative forcing over the outflow region remains inadequate. The enforced shutdown amid the COVID-19 pandemic eased the anthropogenic activities across the country, which helped to examine the magnitude and variability of aerosol loading and subsequent changes in ADRF over IGP and the outflow region of the BoB. Wind trajectory analysis illustrates that the ADRF over the BoB is greater during the days when the winds originated from the IGP region (at the surface −54.2 ± 6.4 W m−2, at the top of the atmosphere, −26.9 ± 3.4 W m−2 and on the atmosphere, 27.0 ± 3.1 W m−2) compared to the seasonal average (−46.3 ± 7.1 W m−2, −24.9 ± 4.0 W m−2 and 20.6 ± 3.2 W m−2, respectively). This indicates that anthropogenic aerosols emission from IGP can contribute an additional 31% of the atmospheric ADRF over the IGP outflow region of the BoB. The reduced aerosol loading during the shutdown period resulted in a reduction of ADRF at the surface, at the top of the atmosphere, and on the atmosphere over the IGP outflow region of the BoB by 22.0 ± 3.1%, 20.9 ± 3.4% and 23.2 ± 3.3%, respectively. This resultant 20–25% reduction in ADRF over the IGP outflow region of BOB matches well with 10–25% reduction in aerosol optical depth (AOD) over the IGP during the shutdown period showing a robust coupling between IGP aerosol emissions and ADRF over the BoB.

Seismic attenuation model for data gap regions using recorded and simulated ground motions

In this study, seismic attenuation model is derived using recorded and simulated ground motions covering the data gap region of the Indo-Gangetic Plains (IGP), employing artificial neural networks (ANN) methodology. Four independent variables moment magnitude (Mw), focal depth, epicentral distance (Repi), and average shear wave velocity up to 30 m depth (Vs30) are selected to predict peak ground acceleration (PGA) and pseudo-spectral acceleration (PSA) (5% damping) between periods 0.01 to 4 s (twenty-five periods in total), utilizing 926 recordings (PESMOS, CIGN and synthetic database). A feed-forward ANN with Levenberg–Marquardt training algorithm is employed for training the network of input and output dataset. The optimal network architecture obtained in this study consists of 4–9–26 input, hidden and target nodes, respectively. In spite of the absence of presumed functional dependencies in ANN methodology, our model captured a number of sound physical features of earthquake ground motion: magnitude scaling, attenuation with distance and radiation damping. Further, the performance of the model is measured by the standard deviation of the error, σ(e), and compared with the four widely used conventional GMPEs applicable for IGP region of India. The standard deviations for our model varied between 0.208 and 0.263 which is less than the classical GMPEs at all twenty-six periods of PSA. Finally, the ANN model performance is compared with recorded ground motions at four stations and conventional GMPEs, and the results affirm that this model is competent to predict the response spectrum with good accuracy for IGP region.