• Volume 128, Issue 5

July 2019

• Uncertainty analysis of rainfall depth duration frequency curves using the bootstrap resampling technique

Rainfall depth duration frequency (DDF) curves are used extensively in many engineering designs. However, due to the sampling error and the uncertainty associated with the parameter estimation process, the DDF curves are subjected to parameter uncertainty. In this study, an evaluation of the uncertainty of the DDF curves in the Kelantan river basin was performed using the bootstrap resampling method. Annual maximum rainfall series for durations of 24, 48, 72, 96 and 120 h were derived from the stochastic rainfall model outputs and fitted to the generalised extreme value (GEV) distribution. The bootstrap samples were generated by resampling with replacement from the annual maximum rainfall series. The relationships that describe the GEV parameters as a function of duration were used to establish the DDF curves. The 95% confidence intervals were used as an indicator to quantify the uncertainty in the DDF curves. The bootstrap distribution of the rainfall depth quantiles was represented by a normal probability density function. The results showed that uncertainty increased with the return period and there was significant uncertainty in the DDF curves. The suggested procedure is expected to contribute to endeavours in obtaining reliable DDF curves, where the uncertainty features are assessed.

• Pyroxenite dykes with petrological and geochemical affinities to the Alaskan-type ultramafics at the northwestern margin of the Cuddapah basin, Dharwar craton, southern India: Tectonomagmatic implications

Two previously reported lamprophyre dykes from the Kalwakurthy area, at the northwestern margin of the Cuddapah basin, Dharwar craton, southern India, are reinvestigated. Petrography reveals that they have an overall cumulate texture and comprise clinopyroxene (dominant phase), amphibole (mostly secondary), magnetite, ilmenite and chromite and are reclassified as clinopyroxenites. The chemistry of clinopyroxene and chromite, bulk-rock major and trace element composition and the Sr–Nd isotopic systematics of the Kalwakurthy dykes strongly favour the involvement of subduction-related processes in their genesis and are strikingly similar to those of the continental arc-cumulates and Alaskan-type ultramafics reported from the supra-subduction type of tectonic settings. Incompatible trace element ratios, involving high field strength elements, of these clinopyroxenites are also suggestive of the fluid-related metasomatism influencing their source regions. Petrogenetic modelling reveals that 10–20% partial melting of the fertile lithospheric mantle source was involved in their genesis. The tectonomagmatic significance of the studied clinopyroxenites is evaluated in light of the existing models invoking a Neoarchaean subduction in the evolution of the Dharwar craton.

• ENSO-induced groundwater changes in India derived from GRACE and GLDAS

This study aims to quantify the interannual variations of groundwater storage changes (GWSCs) over India. GWSCs are derived from the gravity recovery and climate experiment (GRACE) and global land data assimilation system (GLDAS)-Noah life safety model (LSM) for the period 2003–2015. Estimated GWSCs are validated with the satellite altimetry over the six lake stations. The variability of GWSC and altimetry water-level heights are assessed with the cross-correlation and plotting analysis. Annual trends of GWSC and GRACE in terrestrial water storage (TWS) were estimated using the non-parametric Mann–Kendall test and Sen’s slope method. Results suggest that GWSC and TWS have declined in northern India at the rate of $\sim$1.6 cm yr$^{-1}$ and in southern and western central India at the rate of $\sim$0.5 cm yr$^{-1}$. Impacts of short-term climate perturbations such as El Nino and La Nina for the GWSCs are assessed. During the El Nino period, the decline of GWSC over northern India enhanced, whereas during the La Nina period, the recovery of GWSC is evident. These interannual variations of GWSCs over India are attributed by interannual precipitation changes. Under the global warming scenario, the occurrences of El Nino events are likely to enhance in the future, and our findings help the water resource management policy makers for necessary actions during such short-term climate perturbations.

• Petrology and geochemistry of mafic dyke and sills in Cumbum Formation, of the Proterozoic Nallamalai fold belt, Rajampet area, Andhra Pradesh, India

Intensely deformed Proterozoic Nallamalai fold belt (NFB) occupies the eastern part of undeformed, Proterozoic Cuddapah basin and is separated from Cuddapah basin by easterly dipping Rudravaram thrust line. Igneous activity in NFB is represented by intrusive syenite and lamproite dykes. This study brings out the petrological and geochemical character of unreported intrusive dolerite dykes and sills within the Cumbum Formation of NFB. The dykes are undeformed, whereas the sills suffered D1 phase of deformation, although both are petrologically and geochemically similar. The rocks are highly fractionated sub-alkaline tholeiite, consist mainly of clino-pyroxene and plagioclase. Chondrite-normalised rare earth element (REE) plot shows enriched light rare earth element (LREE) and flat heavy rare earth element (HREE). A primitive mantle-normalised multi-element spider diagram shows troughs in Nb, Ta, Ti and Zr indicating subduction zone character. Tectonic discrimination plots indicate both within-plate and subduction zone environment of formation. Geochemical modelling also indicates enriched spinel peridotite as a probable source for dykes and sills. We suggest that the lithospheric mantle beneath NFB got enriched by subduction-derived fluid around 1.6 Ga, and in later stage, these dykes and sills were generated by extension of the enriched lithosphere at different phases in turn inheriting the subduction zone geochemical characters.

• Observation of short-term variations in the clay minerals ratio after the 2015 Chile great earthquake (8.3$M_{\rm{w}}$) using Landsat 8 OLI data

In this paper, we explore the potential use of available free Landsat sensor data to investigate the short-term variations (STV) in the clay mineral ratio (CMR) following the 2015 Chile great moment magnitude earthquake (8.3$M_{\rm{w}}$). The present investigation was carried out in the absence of ground observation data. Landsat 8 Operational Land Imager (OLI)-based multi-temporal imageries of before, after and non-earthquakes were used to derive the above parameter by applying the band ratio approach of bands 6 and 7, where the before and after imageries were compared with non-seismic event images as well as for validation. For the temporal automatic lineament data extraction and final lineament mapping, band 8 (panchromatic) was used by applying the LINE algorithm technique of PCI Geomatica, and ArcGIS 10.5 software, respectively. All these derived products finally interact with the regional geology, fault line and lineament systems. The results reveal that CMR can easily identify the STV at temporal scales before and after the earthquake, while both are normal during non-earthquake time. However, this variation was observed in all three buffer zones (i.e., 50, 100 and 150 km buffer) and highly pronounced especially in the fault adjoining areas. Therefore, we found this research to be effective and could be used as an alternative method for future earthquake studies.

• Study of meteorological impact on air quality in a humid tropical urban area

Urban air quality is highly dynamic and influenced by micrometeorological conditions. In this paper, meteorological impact on criteria air pollutants namely sulphur dioxide (SO$_{2}$), nitrogen dioxide (NO$_{2}$) and particulate matter (PM$_{10}$) were studied using correlation analysis at contrasting locations in the urban environment of Chennai city. Daily average air quality data from five monitoring stations during 2009–2012 were analysed. Out of the five monitoring locations, three locations (Kathivakkam, Thiruvottiyur and Manali) were categorised as industrial locations, General Hospital as a traffic intersection and Taramani as a residential location. The frequency distribution of industrial sites showed higher concentration compared to residential and traffic intersection sites (TS). The increase in annual average concentration of 15–38%, 4–52% and 5–58% was observed for SO$_{2}$, NO$_{2}$ and PM$_{10}$ over the study period, respectively, attributed to vehicular and industrial emissions. SO$_{2}$ showed high correlation with humidity ($R = -0.57$) and cloud cover ($R = 0.63$) during summer. NO$_{2}$ showed a higher correlation with temperature ($R = 0.72$) during monsoon, and with humidity ($R = 0.7$) and cloud cover ($R = 0.75$) during winter. PM$_{10}$ showed moderate correlation with temperature ($R = -0.55$) and wind speed ($R = -0.51$) during summer. Non-parametric tests and Q–Q plot showed the distribution of SO$_{2}$ and NO$_{2}$ as Weibull and lognormal for PM$_{10}$. The wind rose plots depicted predominant wind direction in the south and south-west directions with most observations having a wind speed of $\geq$ 5 m/s. The estimated national ambient air quality index was good for traffic and residential sites. Industrial sites were moderately polluted during the winter season due to high PM$_{10}$ concentration. No exceedances were observed for daily concentration of SO$_{2}$ and NO$_{2}$. Daily average PM$_{10}$ concentration showed exceedances at industrial locations Kathivakkam, Manali and Thiruvottiyur for 305 (92%), 84 (68%) and 164 (53.4%) days, respectively. At TS (General Hospital) and residential site (RS) (Taramani), lower number of exceedances was observed at 25 (13.2%) days and 11 (5.8%) days, respectively.

• The influence of local meteorology and convection on carbon monoxide distribution over Chennai

The influence of local meteorology and convection activities on the vertical distribution of carbon monoxide (CO) over Chennai in southern India was investigated by analysing the measurements of ozone aboard airbus in-service aircraft observations during the years 2012–2013. The seasonal variation of CO in the free troposphere was observed to be different and less pronounced than that in the planetary boundary layer (PBL). The near surface mixing ratio of CO was the highest (190 $\pm$ 68 ppbv) during winter, while enhanced values (117 $\pm$ 11 ppbv) in the free troposphere were observed during post-monsoon. The mixing ratios were the lowest throughout the troposphere during the monsoon. In the PBL, the mixing ratios of CO showed a decline with an increase in wind speed and were the highest (>200 ppbv) under stagnant conditions (1-2 m s$^{-1}$) during winter. The higher CO in the lower free troposphere during the pre-monsoon period is attributed to the stronger biomass burning emissions. In the middle–upper troposphere, higher levels of CO during post-monsoon are due to the enhanced vertical mixing of regional emissions associated with weaker wind shears and frequent convection activities. Overall, the contrasting effects of stronger CO emissions can be observed in winter/pre-monsoon, while the efficient vertical mixing during the monsoon/post-monsoon season governs the observed seasonality of CO. The model for ozone and related chemical tracers, version 4 (MOZART-4) provides a reasonable representation of the convection effect on the CO mixing ratio. This study highlights a need to conduct more observations, especially of aircraft-borne instruments, to understand the effects of regional-scale emissions and dynamics in the middle–upper tropospheric chemistry over South Asia.

• Evolution of extreme rainfall events over Indo-Gangetic plain in changing climate during 1901–2010

Due to climate variability and climate change there is an increase in magnitude and frequency of extreme precipitation events. During the last few decades these extreme rainfall events have been increased in global as well as on regional scale. Our climate is very much affected by the changes in frequency of extreme rainfall events. Particularly, variability of extreme rainfall events has been studied over one of the most valuable Indian region i.e. over Indo-Gangetic plain (IGP). Long term trend in extreme events has been analyzed with the help of IMD classification. The classification is considered for moderate rain (2.5–64.4 mm; category I), heavy rain (64.5–124.4 mm; category II) and very heavy rain (124.5 mm or more; category III) and the categorization of rainfall events is based on daily rainfall for the period 1901–2010 during Indian summer monsoon (JJAS). The significant long term trend in frequency of extreme rainfall events is analyzed using the statistical test. Long term trend analysis shows the significant decreasing trend for categories II and III. However, an increasing rainfall frequency is observed for moderate rainfall events (category I) during the considered period. A significant interannual and inter-decadal fluctuation in rainfall frequency and magnitude were observed over IGP. Events of moderate and heavy rainfall increases during the withdrawal period of Indian summer monsoon, which might contribute in several cases of flood in the region of IGP. In term of distribution and contribution of rainfall in agriculture area categories I and II, rainfall events are more important but changes in rainfall pattern may lead to flood and drought risk over IGP. The policy making decision for disaster risk and food security should be based on spatial as well as temporal variability of rainfall pattern over IGP region.

• Modifications in the trace gases flux by a very severe cyclonic storm, Hudhud, in the coastal Bay of Bengal

A very severe cyclonic storm, Hudhud, made landfall at Visakhapatnam city, the central east coast of India, on 12 October 2014 and it is the most destructive cyclone to ever hit the Indian subcontinent since the past two decades. In order to examine its impact on the flux of trace gases into the atmosphere, a study was made in the coastal Bay of Bengal, off Visakhapatnam, after the cyclone and compared with the pre-cyclone conditions. Hudhud suppressed the vertical mixing of the water column due to the occurrence of strong salinity stratification associated with torrential rainfall. The land run-off and precipitation brought significant amount of ammonium to the coastal waters, resulting in increased pH. The increased pH shifted the inorganic carbon equilibrium towards the formation of bicarbonate, resulting in decreased partial pressure of carbon dioxide (pCO$_{2}$) after the cyclone Hudhud. The undersaturation of carbon dioxide (CO$_{2}$) and nitrous oxide (N$_{2}$O) with respect to atmospheric equilibrium was observed during the post-cyclone period compared to the pre-cyclone period. About 80% of the post-cyclone decrease in N$_{2}$O (>2 nM)) and pCO$_{2}$ (150–200 $\mu$ atm) was contributed by the dilution of coastal waters with the precipitated waters. In contrast, methane (CH$_{4}$) concentrations were increased by 0.5–2.8 nM during the post-cyclone period than in the pre-cyclone period, and were attributed to the input of domestic sewage through land run-off. Dimethyl sulphide (DMS) and the total dimethyl sulphonio-propionate (DMSP$_{t}$) concentrations decreased by 0.4–3.9 and 0.2–6.0 nM, respectively, during the post-cyclone period in comparison with the pre-cyclone period and it was consistent with lower phytoplankton biomass during the former than the latter. The sea-to-air flux of CO$_{2}$, N$_{2}$O and DMS were 1.3 $\pm$ 0.5 mmol C m$^{-2}$d$^{-1}$, 0.9 $\pm$ 0.3 $\mu$ mol m$^{-2}$ d$^{-1}$ and 5.8 $\pm$ 3 $\mu$ mol m$^{-2}$ d$^{-1}$ during the pre-cyclone period, respectively. The corresponding values during the post-cyclone period were lower at $-$2.0 $\pm$ 1 mmol C m$^{-2}$ d$^{-1}$, $-$0.4 $\pm$ 0.1 $\mu$ mol m$^{-2}$ d$^{-1}$ and 2.8 $\pm$ 2 $\mu$ mol m$^{-2}$ d$^{-1}$, respectively. In contrast, the sea-to-air flux of CH$_{4}$ increased from 0.6 to 1.5 $\mu$ mol C m$^{-2}$ d$^{-1}$ from the pre- to the post-cyclone period. This study suggested that the cyclone Hudhud modified the magnitude of the biogenic gas flux to the atmosphere from the coastal Bay of Bengal than hitherto hypothesised.

• Examining climate change impact on the variability of ground water level: A case study of Ahmednagar district, India

This study focuses on examination of variability in the depth to water below ground level (bgl) from 1996 to 2016 in Ahmednagar district of Maharashtra, India in changing climate. Spatial variability of groundwater depth was mapped and classified as shallow, normal, deep and moderate using GIS modeling. Groundwater decline rates during successive decades were examined and critical areas with a significant fall in groundwater levels (GWL) were detected. Present study also focuses on examination of block-wise variability of GWL. Ground water level shows significant variability during 1996–2016 at confidence level 95%. The long term ground water level fluctuation indicates that water levels in major parts of the study area have declined drastically. The depth to ground water in major parts of the study area ranges between 6 and 15 m bgl except in Parner and Shrirampur blocks. Furthermore, depth to water level is >15 mbgl over Sangamner block during the drought year 2004. Present study reports a significant decadal increase of about 0.7 m in water leval decline over the study area. Groundwater depletion over the study area has been observed with decrease in groundwater recharge and increase in temperature and urbanization. Groundwater depletion shows coherent variability with temperature. Our results report a significant decrease of about 0.61 cm/year in ground water recharge as a result of decrease in precipitation and a decadal increase of about 0.1$^{\circ}$ C in temperature over the study area. Evapotranspiration (ET) shows yearly increasing trend of about 9.6 mm over the study area. Results reported in this study highlight the importance of sustainable groundwater resource management over the study area.

• Gravity data interpretation using the particle swarm optimisation method with application to mineral exploration

This paper describes a new method based on the particle swarm optimisation (PSO) technique for interpreting the second moving average (SMA) residual gravity anomalies. The SMA anomalies are deduced from the measured gravity data to eradicate the regional anomaly by utilising filters of consecutive window lengths (s-value). The buried structural parameters are the amplitude factor (A), depth (z), location (d) and shape (q) that are estimated from the PSO method. The discrepancy between the measured and the predictable gravity anomaly is estimated by the root mean square error. The PSO method is applied to two different theoretical and three real data sets from Cuba, Canada and India. The model parameters inferred from the method developed here are compared with the available geological and geophysical information.

• The first report on the chemical (Th–U–Pb) monazite age of the Mul granite pluton, Western Bastar craton, central India and its metallogenic significance

Petrography and the geochemical attributes of the studied Mul granite pluton reveal mixed characteristics of A-type and I-type within-plate granites consistent with an extensional tectonic environment. The dominance of the primary biotite over the primary muscovite suggests its meta-aluminous nature. The dating of monazite from the Mul granitoid pluton by the in situ Th–U–Pb electron probe micro analyser chemical method indicates the tectonomagmatic event around 1602 $\pm$ 27 Ma in the western Bastar craton, Chandrapur district, Maharashtra. The age data possibly represent the emplacement of large bodies of grey granite and attendant monazite crystallisation at $\sim$1600 Ma. This monazite age implies that Mesoproterozoic magmatism is coeval with the formation of the Pranhita Godavari rift in the eastern flank in Maharashtra and associated with the copper and barite mineralisation in Thanewasna and the adjoining areas.

• Arc-parallel compression in the NW Himalaya: Evidence from structural and palaeostress studies of brittle deformation from the clasts of the Upper Siwalik, Uttarakhand, India

The sub-Himalayan Upper Siwalik rocks, between the Main Boundary Thrust (MBT) to the north and the Main Frontal Thrust (MFT) to the south, are intensely brittle sheared and jointed. Our field studies around Dehradun (India) furnished at least eight small-scale brittle slip directions, viz., $\sim$top-to-SW/SSW (up), top-to-SW/SSW (down), top-to-NE/NNE (up), top-to-NE/ENE (down), top-to-NW (down), top-to-SE/SSE (up), top-to-SE/SSE (down) and top-to-NW/NNW (up). Additionally, we report near-vertical faults, four sets of joints (inclined: J$_{1}$ and J$_{2}$; near-vertical: J$_{\rm{1V}}$ and J$_{\rm{2V}}$). Palaeostress analyses using T-TECTO Studio X5 with all joint sets reveal two compression directions $\sim$ENE–WSW and $\sim$NNW–SSE. We propose two possible temporal relations between the joint sets: (i) J$_{1}$, J$_{2}$, J$_{\rm{1V}}$ and J$_{\rm{2V}}$ are coeval ($\sim$ENE–WSW compression) and (ii) J$_{\rm{1V}}$ and J$_{\rm{2V}}$ developed coevally ($\sim$ENE–WSW compression) followed by J$_{1}$ and J$_{2}$ ($\sim$NNW–SSE compression), because arc-parallel compression (if any) occurs later than arc-perpendicular compression. The presence of already well-known strike-slip faults, viz., the Yamuna tear fault and the Ganga tear fault, at high angles, $\sim$55$^{\circ}$ and $\sim$85$^{\circ}$ to the orogenic trend, implies a possible arc-parallel compression in the Siwalik Himalaya in the study area. This $\sim$NNW–SSE compression could also indicate a localised stress reorientation due to the curvature of the Thrust planes, viz., the MFT and the Asan Thrust (as observed in plan view) close to the study area. This study further shows that arc-parallel compression need not be restricted to the inner arc of an orogen, and/or, as in the case of the Himalaya, near the syntaxes.

• Use of genetic algorithm in reservoir characterisation from seismic data: A case study

In the present paper, a seismic inversion based on genetic algorithm (GA) is performed to characterise the reservoir using seismic data only from the Blackfoot field, Alberta, Canada. The algorithm is first tested on synthetically generated data to optimise the GA parameters. The error analysis between the inverted and the expected results suggested that the performance of algorithm is exceptionally satisfactory. Thereafter, the inversion is performed for real seismic data from the Blackfoot field. The seismic data is first inverted for acoustic impedance section and then it is transformed into the velocity and density sections using the relation derived from the well-log data. The interpretation of the inverted/derived results depicts a low-amplitude anomaly zone between 1055 and 1065 ms time interval, which is characterised as a reservoir. The results demonstrate the efficacy and applicability of the GA in reservoir characterisation from the seismic data alone. This study is very helpful for the offshore projects where the information about well logs are missing.

• Seasonal variation of evapotranspiration and its effect on the surface energy budget closure at a tropical forest over north-east India

This study uses 1 yr of eddy covariance (EC) flux observations to investigate seasonal variations in evapotranspiration (ET) and surface energy budget (SEB) closure at a tropical semi-deciduous forest located in north-east India. The annual cycle is divided into four seasons, namely, pre-monsoon, monsoon, post-monsoon and winter. The highest energy balance closure (76%) is observed during pre-monsoon, whereas the lowest level of closure (62%) is observed during winter. Intermediate closure of 68% and 72% is observed during the monsoon and post-monsoon seasons, respectively. Maximum latent heat flux during winter (150 W m$^{-2}$) is half of the maximum latent heat (300 W m$^{-2}$) flux during the monsoon. ET is a controlling factor of SEB closure, with the highest rates of closure corresponding to the periods of the highest ET. The Bowen ratio ranges from 0.93 in winter to 0.27 during the monsoon. This is the first time the role of ET in the seasonal variation of SEB closure has been reported for any ecosystem in north-east India using EC measurements.

• Black carbon aerosols from the coal seam of eastern India: A real-time analysis with statistical validation

Underground coal seam fire is one of the serious problems caused by coal mining activities. Hence, the present study is focused on investigating the potential emission of black carbon (BC) and its dispersion from the fire-affected area located in the Jharia coal field, Dhanbad district of the Jharkhand state of India. The real-time BC concentration measurements in the active fire area and the adjacent neighbouring urban area were studied and reported. Results showed an average concentration of BC was 12.54 $\mu$g m$^{-3}$ in the fumes/smokes emitting from the surface cracks and vents at the fire-affected zone. The continuous probability distribution functions, i.e., lognormal, gamma and Weibull, were used to fit the BC data individually, and among these lognormal fits, the best were for the medium-range values. Furthermore, the robustness of the obtained BC concentration was also explained by these models. All fitness was in good agreement, in the studied area, with the coefficient of regression ranging between 0.84 and 0.96. Both the experimental and predicted results clearly indicated the contribution of the BC that discharged from the coal seam fire as a source of particulate pollutant. Spatial modelling was also performed to validate the experimental consistency of BC concentration while the model was in good agreement with the underground coal fire zone as compared to the rest.

• Mid–late Holocene fluvial aggradational landforms and morphometric investigations in the southern front of the Shillong plateau, NE India

The present study is an attempt to understand the antiquity of the preserved fluvial landforms and its response to the climate–tectonics nexus through geomorphological investigations along the Jadukata, Umpung, Umngot and Umtongoi rivers in the southern front of the Shillong plateau (SP), NE India. Sedimentological characteristics, chronological analyses and morphotectonic parameters were used to describe the spatial and temporal variability in the patterns of aggradation, landform evolution and neotectonic influences in the study. Our results indicate that valley aggradation processes occurred around the transitional zone in the southern front of the SP during the mid–late Holocene era along with a hiatus in sediment deposition after 4.3 ka. Sediment generation and aggradation is modulated by precipitation anomalies associated with the Indian Summer Monsoon (ISM) variability whereas morphometric analysis suggests that activity along the Dauki–Dapsi fault has been contributing to the uplift-related deformation. Sedimentological observation supported by optically stimulated luminescence chronology obtained on palaeoflood deposits, valley-fill fluvial terraces and alluvial fans indicate their deposition during three pluvial phases: (i) 5.3–4.3 ka, (ii) 2.4–1.0 ka and (ii) 0.7–0.3 ka. Our data indicate that valley aggradation and geomorphic processes in the southern part of SP responded to short-term changes in the ISM variability with contributions from the morphotectonic activities associated with the Dauki–Dapsi fault during the late Holocene period.

• MOS guidance using a neural network for the rainfall forecast over India

In the present study, a model output statistics (MOS) guidance model was developed by using the neural network technique for a bias-corrected rainfall forecast. The model was developed over the Indian window (0–40$^{\circ}$N and 60–100$^{\circ}$E) by using the observed and global forecast system (GFS) T-1534 model output (up to 5 days) at a 0.125$^{\circ} \times$ 0.125$^{\circ}$ regular grid during the summer monsoon (June–September) 2016. The skill of the developed MOS model forecast against the observed 0.125$^{\circ} \times$ 0.125$^{\circ}$ grid rainfall data is obtained for the summer monsoon (June–September) 2017. The skill of the MOS model rainfall forecast is found to show good improvement over the T-1534 model’s direct forecast over the Indian window. In general, the T-1534 model’s direct forecast shows high skill but the forecast obtained by using the MOS model shows better skill than the direct model’s forecast, although a major improvement is seen for the Day 1 forecast at the national level. So the skill of the bias-corrected rainfall forecast by using the MOS guidance and the T-1534 model output is high and has the potential of being used as an operational forecast over the Indian region.

• Potential impacts of climate change on groundwater resources: A multi-regional modelling assessment

The complexity of understanding the groundwater resources in relation to climate change is caused by direct and indirect effects of climate change on hydrological processes. The study herein aims at implementing a physically based groundwater model to investigate the effects of climate change on groundwater system under 15 general circulation models (GCMs) in a semi-arid region from 2020 to 2044. A non-parametric probability density function estimator was used to quantify the level of uncertainties in the simulations. The method was applied to an area of 2073 km$^{2}$ in southwest Iran, consisting of five plains: western Dez, eastern Dez, Sabili, Deymche and Lor. The results indicate that there is a decline in the recharge in April, May, June and October. The range of changes in the recharge was determined to be between $-$10% and +13% in the Sabili plain, $-$6% and +10% in the Deymche plain, $-$4% and +10% in the western-Dez plain, $-$6% and +26% in the eastern-Dez plain, and $-$40% and +100% in the Lor plain. The most significant decline in the groundwater level occurred in the Sabili plain in September. The largest uncertainty in the simulation of recharge under GCM scenarios was determined to be in August, September and December. This study highlights that climate change can have a significant effect on groundwater resources in the region that reinforces the need for groundwater management plans and a long-term perspective.

• GIS-based prediction of groundwater fluoride contamination zones in Telangana, India

Groundwater is the only perennial water resource available to rural communities, especially in semi-arid regions. This study aims to provide an overview of fluoride-contaminated groundwater in the Telangana, India, by predicting potentially affected areas. The prevalence of endemic fluorosis in different parts of Telangana has been widely reported. Therefore, it is necessary to demarcate the fluoride-affected areas to adopt the remedial measures. In this context, the available information on related environmental variables such as geological settings, hydro-morphological inputs, climatic information and soil properties have been integrated as thematic layers in an ArcGIS environment. The thematic layers and their features were assigned with suitable weights, which were normalised using the analytic hierarchy process to obtain final ranks and the weighted overlay analysis method was carried out to delineate the potential fluoride contamination (PFC) zones. The entire state was classified into four broad categories, i.e., very high (17.6%), high (15.8%), medium (32.7%) and low (33.9%), in terms of groundwater fluoride enrichment. A comparison of the output map and the reported data indicates that the PFC zone model could explain 68.7% of fluoride variation. This study is the first such attempt to offer a regional-scale PFC zone for an entire state and offers a first-hand insight into the severity of fluoride contamination.

• Improving precipitation forecasts over Iran using a weighted average ensemble technique

In this paper, the ensemble-weighted mean (ENSWM) technique is experimented for improving 24- to 72-hr precipitation forecasts over Iran during autumn and winter 2011 and 2012. The ensemble prediction system (EPS), used in this research, consists of nine different configurations of the weather research and forecasting model. In this technique, weights for each ensemble member at each grid point are assigned on the basis of the correlation coefficient (CC) between ensemble members and observed daily rainfall during a training period. Apart from ENSWM, precipitation forecasts using the simple ensemble mean (ENSM) are also generated and compared. Results showed that, in general, the forecast errors are relatively high along the coasts of the Caspian Sea in northern and at the Zagros mountainous areas located in western Iran. The skill of the rainfall forecasts of the ENSWM is examined against ENSM and individual members of the ensemble. The 24- to 72-hr forecasts are evaluated using common statistical scores including root mean-squared error (RMSE), and anomaly CC (ACC) for continuous forecasts and probability of detection (POD) score and threat score for categorical forecasts. The comparison reveals that the ENSWM is able to provide more accurate forecast of rainfall over Iran by taking the strength of each constituent member of the ensemble. It has been further found that the precipitation forecast skill of ENSWM is higher than ENSM and each ensemble member in the short-range time scale over Iran. The rainfall prediction skill over Iran was improved significantly using the weighted ENSWM technique. Results clearly show the advantage of using an EPS for the prediction of precipitation over the country vs. a single deterministic forecast for operational purposes. The RMSE of 24-, 48- and 72-hr forecasts in ENSWM relative to ENSM is reduced by 2, 2 and 5%, respectively. The CC increased by 15% in the ENSWM relative to ENSM.

• A study of frost occurrence and minimum temperatures in Iran

In this research, the frequency of frost is analysed from 95 synoptic stations for the period 1990–2015. This information was categorised by a fuzzy c-approach clustering algorithm and indicated that Iran is classified into five clusters with the aid of the frost-occurrence frequencies. The greatest frequency of days with frost prevalence is located in Cluster 1 that consists of Sarab station with an average annual frequency of 141.1 days over the period 1990–2015. The least frequent is found in Cluster 5 that consists of the stations positioned along the south and north coasts. Spatial association for the frequency of incidence of frost days also includes a dependence on elevation and latitude of stations, as well as their situation inside the course of external synoptic systems, bodily and geomorphological features and local climate. Also, a study of daily minimum temperature displays a widespread warming trend at some stage during this period, and has discovered an increase in the index of the number of tropical nights, warmest nights and coldest nights and decreasing trends have been determined in the number of frost days, cool nights and cold spell period index over most regions of Iran.

• The role of the F-region vertical drift on the onset time of the equatorial spread F over Ilorin, Nigeria

The equatorial ionosphere often shows the occurrence of plasma-density irregularities and velocity fluctuations with a broad range of scale sizes and amplitudes. These irregularities in the F-region are commonly referred to as the equatorial spread F (ESF) and they are predominantly a night-time phenomenon. The vertical drift of ionisation to higher altitudes post-sunset hours has been suggested to be responsible for the occurrence of these irregularities. We have therefore used all the available ionograms at Ilorin, Nigeria (latitude = 8.48$^{\circ}$N, longitude= 4.67$^{\circ}$W and dip= 4.1$^{\circ}$S) to study the occurrence of ESF and the effect of the F-region drift on the occurrence of ESF. The available data at Ilorin, though not continuous, cover a period of 6 yrs (i.e., 2002, 2005, 2006, 2007, 2008 and 2010). The F-region vertical drift velocity was estimated starting from around local sunset until the onset of ESF, and the maximum value for a night ($V_{Z,\rm{max}}$) is used to represent the strength of the $E \times B$ drift for that night. Results obtained showed that the percentage occurrence of ESF increases with the increase in solar activities. A seasonal trend is also observed in the occurrence frequency; occurrence seems to be more frequent during and around the equinox periods. The onset time or the time of commencement (TOC) of ESF was observed to vary from day to day. Also, $V_{Z,\rm{max}}$ seems to increase with the increase in solar activities, which in turn influences the TOC of ESF. It was found that the higher the $V_{Z,\rm{max}}$, the closer the TOC was found to be to the local time $V_{Z,\rm{max}}$. In a few cases, there was no noticeable movement of ionisation prior to the commencement of the ESF, and this might be pointing to the fact that the drifting of ionisation to a higher altitude is not the only condition for the occurrence of ESF. Other conditions that have been identified to play a role in ESF occurrence are thermospheric neutral dynamics, equatorial thermodynamic meridional winds and the post-sunset base height of the F-layer ($h^{\prime}F$).

• A case study on bright band transition from very light to heavy rain using simultaneous observations of collocated X- and Ka-band radars

The observations of bright band carried out simultaneously with X- and Ka-band radars for the first time over the Indian region have been examined to reveal various contrasting characteristics of bright band at the two wavelengths. The study reports the bright band observations on September 12–13, 2015 at millimeter and centimeter wavelengths and brings out a comparative analysis of the bright band features (e.g., intensity, thickness, height, etc.) under three different rain conditions ranging from very light (<0.1 mm/hr) to light (0.1–3 mm/hr) to heavy (3–5 mm/hr). It is seen that the bright band region at Ka-band is always narrower and situated at a higher altitude than at X-band frequency. Our analysis shows that at Ka-band frequency, the polarimetric fields like LDR can be utilized to detect and determine the bright band features using an appropriate selection of a threshold value of LDR, which is found to be −22 dB in this study and could be associated reasonably with the top and bottom heights of the bright band. This study explores the potential of both radars, particularly the Ka-band radar for probing the bright band effect and estimating its features which would be helpful to improve the quantitative estimates of precipitation.

• Differences in natural gamma radiation characteristics of Erinpura and Malani granites in NW India

In NW India, large volumes of exposed Neoproterozoic basement rocks are formed by two magmatic suites, Erinpura granites as a late thermal event with respect to the $\sim$1 Ga Delhi Orogeny and the younger Malani igneous suite (770–750 Ma). Average uranium and thorium equivalent concentrations (in ppm) inferred from spectroscopic gamma radiation survey are higher in Malani rocks (Th 47.33 ppm and U 6.95 ppm) as compared to the Erinpura granites (Th 33.55 ppm and U 4.77 ppm). These values are considerably above the granite world average (Th 14.8 $\pm$ 13.2 ppm; U 3.93 $\pm$ 3.27 ppm). High U (up to 19 ppm) and Th (up to 88 ppm) in some Malani granites and a constant Th–U ratio of 7 points to a high degree of fractionation of the felsic magma. Higher radioelement concentration in the east (Mirpur granite) as compared to the west (Jaswantpura granite) is substantiated by geochemical data. Areas to the west and east of the Sirohi frontal thrust show differences, most likely a consequence of anatexis in the eastern sector. A high linear correlation between inductively coupled plasma mass spectrometry and gamma-ray data underlines the suitability of in-situmeasurements for the determination of U and Th concentrations during a field survey providing basic information for future petrogenetic and risk-hazard studies in this granitic terrain.

• Isotopic fingerprinting of fluid circulation at the terminal stage of the Himalayan orogeny: An example from the Himalayan forearc basin, Indus Tsangpo suture zone, Ladakh, India

Quartz and calcite veins are omnipresent in the Indus basin sedimentary rocks (IBSRs) of the Indus Tsangpo suture zone (ITSZ) which were formed by the accumulation of sediments derived from both sides of the tectonic plate. These veins appear to have formed just after the sediment diagenesis and were deformed together with the IBSR. The veins were studied for their rare earth elemental and isotopic geochemistry (C–O–Sr–Pb). The light rare earth element/mid rare earth element with an Eu/Eu* ratio of the veins (quartz and calcite) is >1 for the northern side (Tibetan side) and <1 for the southern side, indicating a mantle/magmatic and marine-related fluid source, respectively. The carbon, oxygen and strontium isotopes range from -14 per thousand to -1 per thousand VPDB, +5.7 per thousand to +24.9 per thousand Vienna standard mean ocean water and 0.7056 to 0.7099, respectively. The Sr–O mixing model points towards the mantle-enriched fluid on the northern side of the IBSR, whereas on the southern side, the fluid was nearly marine. The intermixing of the fluid took place in the middle part of the Indus basin sediments comprising a mixed litho-unit succession. Similar characteristics of vein fluids with the host rocks indicate the derivation of fluids from the associated host IBSR, further substantiated by the lead isotopic systematics.

• The geological site characterisation of the Mandla region, Eastern Deccan Volcanic Province, Central India

Detailed geological studies were carried out on the basaltic sequences along the Jabalpur–Niwas, Jabalpur–Chutka and Jabalpur–Mandla traverses covering an area of about 12 km $\times$ 15 km to characterise various basaltic lava flows and their behaviour on seismotectonics and geodynamic setting of their formation in the Mandla region of the Eastern Deccan Volcanic Province (EDVP). The studies involve an analysis of the satellite images for the identification of lineaments/faults and field geological studies consisting of geological controls such as ground check, thickness of fractures and orientation along the acknowledged lineaments/faults. The results of the present research comprising 65 lineaments/faults mainly belonging to two geometric groups, minor and major dominantly in the NW–SE and the NE–SW and altered strata varying lithology (weathered to compact basalts) are recognised in the study area. Based on their extent, 57 lineaments have been classified as minor (<100 km) trends in three different orientations, i.e., NNE–SSW, ESE–WNW and ENE–WSW, whereas 8 lineaments were classified as intermediate (300–100 km) trends in NNE–SSW. No major (>300 km) lineaments are noticed in the study region. The field geological investigations have facilitated the recognition of 10 flows with different characteristic features and a variety of volcanic structures such as columnar, vesicular, amygdaloidal, inflated pahoehoe lava flows and red bole interflow horizons have been documented. Basement rocks of these Deccan basalt lavas are represented by Tirodi Biotite gneisses, quartzite, quartz–mica schists and crystalline limestone in the SE part of the study area of the Mandla region. The present study will help evaluate the localised site characterisation for urban planning and setting up major civil structures.

• Correction to: Estimation of coda Q for the eastern Indian craton

• # Journal of Earth System Science

Current Issue
Volume 128 | Issue 8
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019

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