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      Volume 125, Issue 3

      April 2016,   pages  443-675

    • Response of streamflow to projected climate change scenarios in an eastern Himalayan catchment of India

      K T Senzeba S Rajkumari A Bhadra A Bandyopadhyay

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      Snowmelt run-off model (SRM) based on degree-day approach has been employed to evaluate the change in snow-cover depletion and corresponding streamflow under different projected climatic scenarios foran eastern Himalayan catchment in India. Nuranang catchment located at Tawang district of ArunachalPradesh with an area of 52 km^2 is selected for the present study with an elevation range of 3143–4946 mabove mean sea level. Satellite images from October to June of the selected hydrological year 2006–2007were procured from National Remote Sensing Centre, Hyderabad. Snow cover mapping is done usingNDSI method. Based on long term meteorological data, temperature and precipitation data of selectedhydrological year are normalized to represent present climatic condition. The projected temperatureand precipitation data are downloaded from NCAR’s GIS data portal for different emission scenarios(SRES), viz., A1B, A2, B1; and IPCC commitment (non-SRES) scenario for different future years (2020,2030, 2040 and 2050). Projected temperature and precipitation data are obtained at desired locationby spatially interpolating the gridded data and then by statistical downscaling using linear regression.Snow depletion curves for all projected scenarios are generated for the study area and compared withconventional depletion curve for present climatic condition. Changes in cumulative snowmelt depth fordifferent future years are highest under A1B and lowest under IPCC commitment, whereas A2 andB1 values are in-between A1B and IPCC commitment. Percentage increase in streamflow for differentfuture years follows almost the same trend as change in precipitation from present climate under allprojected climatic scenarios. Hence, it was concluded that for small catchments having seasonal snowcover, the total streamflow under projected climatic scenarios in future years will be primarily governedby the change in precipitation and not by change in snowmelt depth. Advancing of depletion curves fordifferent future years are highest under A1B and lowest under IPCC commitment. A2 and B1 values arein-between A1B and IPCC commitment.

    • Role of debris cover to control specific ablation of adjoining Batal and Sutri Dhaka glaciers in Chandra Basin (Himachal Pradesh) during peak ablation season

      Parmanand Sharma Lavkush K Patel Rasik Ravindra Ajit Singh K Mahalinganathan Meloth Thamban

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      As part of the on-going annual mass balance measurements on Batal and Sutri Dhaka glaciers, observationswere made during peak ablation (August–September) season in 2013 to understand the responseof debris covered and clean-ice (debris free) glacier surface to melting processes. Though, both the Bataland Sutri Dhaka glaciers have almost similar geographical disposition, Batal shows extensive debriscover (90% of the ablation area), while the latter is free from debris (only 5% of the ablation area). Thethickness of debris in Batal glacier is inversely proportional to altitude, whereas Sutri Dhaka mostlyexperienced debris-free zone except snout area. Observation revealed that the vertical gradient of ablationrate in ablation area is contrastingly opposite in these two glaciers, reflecting significant control ofdebris thickness and their distribution over glacier surface on the ablation rates. While different thickness(2–100 cm) of debris have attenuated melting rates up to 70% of total melting, debris cover of 2 cm thickness has accelerated melting up to 10% of the total melting. Estimated melt ratio revealsthat about 90% of the ablation area has experienced inhibited melting in Batal glacier, whereas only lessthan 5% ablation area of Sutri Dhaka has undergone inhibited melting. Comparison of topographicalmaps of 1962 with successive satellite images of the area demonstrates a terminus retreat of 373 ± 33.5 mand 579 ± 33.5 m for Batal and Sutri Dhaka glaciers for the period 1962–2013, respectively.

    • Role of land state in a high resolution mesoscale model for simulating the Uttarakhand heavy rainfall event over India

      P V Rajesh S Pattnaik D Rai K K Osuri U C Mohanty S Tripathy

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      In 2013, Indian summer monsoon witnessed a very heavy rainfall event (>30 cm/day) over Uttarakhandin north India, claiming more than 5000 lives and property damage worth approximately 40 billionUSD. This event was associated with the interaction of two synoptic systems, i.e., intensified subtropicalwesterly trough over north India and north-westward moving monsoon depression formed over the Bayof Bengal. The event had occurred over highly variable terrain and land surface characteristics. Althoughglobal models predicted the large scale event, they failed to predict realistic location, timing, amount,intensity and distribution of rainfall over the region. The goal of this study is to assess the impactof land state conditions in simulating this severe event using a high resolution mesoscale model. Theland conditions such as multi-layer soil moisture and soil temperature fields were generated from HighResolution Land Data Assimilation (HRLDAS) modelling system. Two experiments were conductednamely, (1) CNTL (Control, without land data assimilation) and (2) LDAS, with land data assimilation(i.e., with HRLDAS-based soil moisture and temperature fields) using Weather Research and Forecasting(WRF) modelling system. Initial soil moisture correlation and root mean square error for LDAS is 0.73and 0.05, whereas for CNTL it is 0.63 and 0.053 respectively, with a stronger heat low in LDAS. Thedifferences in wind and moisture transport in LDAS favoured increased moisture transport from ArabianSea through a convectively unstable region embedded within two low pressure centers over Arabian Seaand Bay of Bengal. The improvement in rainfall is significantly correlated to the persistent generation ofpotential vorticity (PV) in LDAS. Further, PV tendency analysis confirmed that the increased generationof PV is due to the enhanced horizontal PV advection component rather than the diabatic heatingterms due to modified flow fields. These results suggest that, two different synoptic systems merged bythe strong interaction of moving PV columns resulted in the strengthening and further amplificationof the system over the region in LDAS. This study highlights the importance of better representation ofthe land surface fields for improved prediction of localized anomalous weather event over India.

    • Assessing the vegetation canopy influences on wind flow using wind tunnel experiments with artificial plants

      Youngjoo Hong Dongyeob Kim Sangjun Im

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      Wind erosion causes serious problems and considerable threat in most regions of the world. Vegetation on the ground has an important role in controlling wind erosion by covering soil surface and absorbingwind momentum. A set of wind tunnel experiments was performed to quantitatively examine the effect of canopy structure on wind movement. Artificial plastic vegetations with different porosity and canopyshape were introduced as the model canopy. Normalized roughness length $(Z0/H)$ and shear velocity ratio $(R)$ were analyzed as a function of roughness density ($\lambda$). Experiments showed that $Z0/H$ increasesand R decreases as λ reaches a maximum value, $\lambda_{max}$, while the values of $Z0/H$ and $R$ showed little change with $\lambda$ value beyond as $\lambda_{max}$.

    • Effects of changes in vegetation on precipitation in the northern Tianshan Mountains evaluated using multiple time scales

      Qinming Qinming Sun Tong Liu Zhiquan Han Yongping Wu Bai-Lian Li

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      This study used a combination of the wavelet cross-correlation technique and numerical analysis ofvegetative feedback to study the role of climate–vegetation feedback from 1981 to 2009 in the northernTianshan Mountains, Xinjiang Province, China. The study area included the Irtysh River, the Bortalaand Ili River valleys, the northern slopes of the Tianshan Mountains, and the western Junggar Basin.The feedback effects of changes in vegetation on precipitation appeared to vary in these five regionswhen different time scales are used to examine them. The most useful time scale was generally found tobe 4–6 months. Time lag was another characteristic of this process, and the optimal time lag was 3–4months. Nevertheless, optimal time scale and time lag did not differ significantly in these five regions. Inthis way, the correct time scale of the effects of variations in vegetation on precipitation in this cold, aridarea was found. This time scale and time lag can be assessed through wavelet cross-correlation analysis.Then numerical analysis can be used to improve the accuracy of the analysis.

    • Impact of hybrid GSI analysis using ETR ensembles

      V S Prasad C J Johny

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      Performance of a hybrid assimilation system combining 3D Var based NGFS (NCMRWF Global ForecastSystem) with ETR (Ensemble Transform with Rescaling) based Global Ensemble Forecast (GEFS) ofresolution T-190L28 is investigated. The experiment is conducted for a period of one week in June 2013and forecast skills over different spatial domains are compared with respect to mean analysis state.Rainfall forecast is verified over Indian region against combined observations of IMD and NCMRWF.Hybrid assimilation produced marginal improvements in overall forecast skill in comparison with 3DVar. Hybrid experiment made significant improvement in wind forecasts in all the regions on verificationagainst mean analysis. The verification of forecasts with radiosonde observations also show improvementin wind forecasts with the hybrid assimilation. On verification against observations, hybrid experimentshows more improvement in temperature and wind forecasts at upper levels. Both hybrid and operational3D Var failed in prediction of extreme rainfall event over Uttarakhand on 17 June, 2013.

    • Post-glacial landform evolution in the middle Satluj River valley, India: Implications towards understanding the climate tectonic interactions

      Shubhra Sharma S K Bartarya B S Marh

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      Late Quaternary landform evolution in monsoon-dominated middle Satluj valley is reconstructed using the fragmentary records of fluvial terraces, alluvial fans, debris flows, paleo-flood deposits, and epigenetic gorges. Based on detailed field mapping, alluvial stratigraphy, sedimentology and optical chronology, two phases of fluvial aggradations are identified. The older aggradation event dated between ∼13 and 11 ka (early-Holocene), occurred in the pre-existing topography carved by multiple events of erosion and incision. Climatically, the event corresponds to the post-glacial strengthened Indian summer monsoon (ISM). The younger aggradation event dated between ∼5 and 0.4 ka (mid- to late-Holocene), was duringthe declining phase of ISM. The terrain witnessed high magnitude floods during transitional climate (∼6.5–7 ka). The fluvial sedimentation was punctuated by short-lived debris flows and alluvial fans during the LGM (weak ISM), early to mid-Holocene transition climate and mid- to late-Holocene decliningISM. Based on the terrace morphology, an event of relatively enhanced surface uplift is inferred after late Holocene. The present study suggests that post-glacial landforms in the middle Satluj valley owe their genesis to the interplay between the climate variability and local/regional tectonic interactions.

    • Long term changes in forest cover and land use of Similipal Biosphere Reserve of India using satellite remote sensing data

      K R L Saranya C Sudhakar Reddy

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      The spatial changes in forest cover of Similipal Biosphere Reserve, Odisha, India over seven decades(1930–2012) in the last century has been quantified by using multi-temporal data from different sources.Over the period, the forest cover reduced by 970.8 km2 (23.6% of the total forest), and most significantlyduring the period, 1930–1975. Human-induced activities like conversion of forest land for agriculture,construction of dams and mining activities have been identified as major drivers of deforestation. Spatialanalysis indicates that 399 grids (1 grid = 1 × 1 km) have undergone large-scale changes in forest cover(>75 ha) during 1930–1975, while only 3 grids have shown >75 ha loss during 1975–1990. Annual netrate of deforestation was 0.58 during 1930–1975, which has been reduced substantially during 1975–1990 (0.04). Annual gross rate of deforestation in 2006–2012 is indeed low (0.01) as compared to thenational and global average. This study highlights the impact and effectiveness of conservation practicesin minimizing the rate of deforestation and protecting the Similipal Biosphere Reserve.

    • Assessing the suitability of benthic foraminiferal morpho-groups to reconstruct paleomonsoon from Bay of Bengal

      M Manasa Rajeev Saraswat Rajiv Nigam

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      Temporal changes in benthic foraminiferal morpho-groups were suggested as an effective proxy to reconstructpast monsoon intensity from the Arabian Sea. Here, in order to test the applicability of temporalvariation in morpho-groups to reconstruct past monsoon intensity from the Bay of Bengal, we havedocumented recent benthic foraminiferal distribution from the continental shelf region of the northwesternBay of Bengal. Based on the external morphology, benthic foraminifera were categorized intorounded symmetrical (RSBF) and angular asymmetrical benthic foraminifera (AABF). Additionally, afew other dominant groups were also identified based on test composition (agglutinated, calcareous) andabundance (Asterorotalids and Nonions). The relative abundance of each group was compared with theambient physico-chemical conditions, including dissolved oxygen, organic matter, salinity and temperature.We report that the RSBF are abundant in comparatively warm and well oxygenated waters of lowsalinity, suggesting a preference for high energy environment, whereas AABF dominate relatively cold,hypersaline deeper waters with low dissolved oxygen, indicating a low energy environment. The agglutinatedforaminifera, Asterorotalids and Nonions dominate shallow water, low salinity regions, whereasthe calcareous benthic foraminiferal abundance increases away from the riverine influx regions. Foodavailability, as estimated from organic carbon abundance in sediments, has comparatively less influenceon faunal distribution in the northwestern Bay of Bengal, as compared to dissolved oxygen, temperatureand salinity. We conclude that the factors associated with freshwater influx affect the distributionof benthic foraminiferal morpho-groups in the northwestern Bay of Bengal and thus it can be used toreconstruct past monsoon intensity from the Bay of Bengal.

    • Petrogenesis, zircon U–Pb age, and geochemistry of the A-type Mogou syenite, western Henan Province: Implications for Mesozoic tectono-magmatic evolution of the Qinling Orogen

      Xinyu He Jionghui Wang Changming Wang Emmanuel John M Carranza Liang Chen Bin Wu

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      The Mogou syenite intruded into the Mesoproterozoic Xiong’er Group is the main lithostratigraphic unit, along the southern margin of the North China Craton (NCC). This paper reports zircon LAICP-MS data, whole-rock major and trace element compositions of late Triassic magmatic rocks in the Mogou syenite, in order to constrain the formation age of the Mogou syenite, research the origin and evolution of the magma and analyse the geodynamic setting of the Qinling Orogen (QO) in Late Triassic. These rocks consist of medium- to coarse-grained syenite and fine-grained quartz syenite. Zircon U–Pb dating yields a crystallization age of 226.5±2.7 Ma. The syenites are characterized by highSiO_2 (63.49–72.17%), alkali (K_2O+Na_2O of 11.18–15.38%) and potassium (K_2O/Na_2O of 2.88–28.11), are peralkaline or metaluminous (molar A/CNK of 0.87–1.02) and belong to shoshonite series. The syenites have ΣREE of 33.01–191.30 ppm, LREE/HREE of 14–20, (La/Yb)N of 11–24, with LREE-richdistribution pattern and obvious differentiation between HREE and LREE. Eu anomalies are positive for the medium- to coarse-grained syenite and weakly negative for the fine-grained quartz syenite. In addition, the syenites are enriched in large-ion lithophile elements (Ba, K, Sr, and Pb) but depleted inhigh strength field elements (Ti, Ta, Nb, Zr, and Hf), and have high differentiation indices of 91.69–97.06. These geochemical features indicate that the primary magma of the Mogou syenite most likely originated from a mantle source with minor crustal component, and underwent a fractional crystallizationprocess during its emplacement. The late Triassic A-type Moguo syenite along the southern margin of the NCC was generated in the late stage of the syn-collision event of QO, recording a transition periodfrom compression to extension at around 227 Ma.

    • Rb–Sr and Sm–Nd study of granite–charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

      M Chandra Sekaran Rajneesh Bhutani S Balakrishnan

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      Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb–Sr biotite and Sm–Nd whole-rock isochron ages indicate a regional uplift and cooling at ∼550 Ma. The initialNd isotope ratios (ε^t_{Nd} = −20 to −22) and Nd depleted-mantle model ages (T_{DM} = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (ε^t_{Nd} = −29 and T_{DM} =>3.2 Ga). TheRb–Sr whole-rock data and initial Sr–Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an ‘apparent whole-rock isochron’. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean–Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which ‘prepared’ the residual crust to sustain the high P–T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.

    • Mapping sediment thickness of Islamabad city using empirical relationships: Implications for seismic hazard assessment

      Sarfraz Khan M Asif Khan

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      Soft sediments make an important component of the subsurface lithology, especially in areas underlain by river/stream basins. Occupying a position directly above the bedrock up to the land surface, these soft sediments can range in thickness from few centimeters to hundreds of meters. They carry a specialnuisance in seismic hazards, as they serve as a source of seismic amplification that may enhance the seismic shaking of many folds. Determination of the thickness of the soft sediments is therefore crucial in seismic hazard analysis. A number of studies in recent years have demonstrated that frequency andamplitude spectrum obtained from the noise measurements during the recording of natural seismicitycan be used to obtain thickness of soft sediments covering the bedrock. Nakamura (1989) presented atechnique to determine such spectrum using ratio of horizontal to vertical components of the Rayleighwaves. The present study is based on an extensive set of microtremor measurements carried out in theIslamabad city, Pakistan. Fundamental frequencies were obtained from weak motion sensors and TrominoEngy Plus instruments to show that the correlation is clearly valid for a wide range of sediment thickness.A simple formula was derived for the investigated area to determine directly the thickness of sedimentsfrom the main peaks in the H/V spectrum for seismometer and Tromino data separately. A comparisonis made between sediment thicknesses derived from empirical relations developed in this study withthose given in literature to demonstrate a positive correlation. The correlation of instrumental resonantfrequencies with calculated resonant frequencies (theoretical) suggests that the relation derived from thenoise measurements mostly depends on the velocity depth function of the shear wave. The fundamentalfrequency of the main peak of spectral ratio of H/V using the both instruments correlates well withthe thickness of sediments at the site obtained from the borehole data. It is found out that there is awide variation in soft-sediment thickness in the Islamabad area, but as a general rule, soft sedimentsare thicker adjacent to stream courses compared to the areas intervening the streams. The distributionof sediments in the studied area is illustrated by means of cross sections constructed from results ofthe microtremor analyses and available borehole data, which provides a visual distribution of the softsediments underlying the Islamabad city.

    • A comparative study on the landslide susceptibility mapping using evidential belief function and weights of evidence models

      Qiqing Wang Wenping Li Yanli Yanli Wu Yabing Pei Maolin Xing Dongdong Yang

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      The purpose of this study is to produce landslide susceptibility map of a landslide-prone area (DaguanCounty, China) by evidential belief function (EBF) model and weights of evidence (WoE) model tocompare the results obtained. For this purpose, a landslide inventory map was constructed mainly basedon earlier reports and aerial photographs, as well as, by carrying out field surveys. A total of 194landslides were mapped. Then, the landslide inventory was randomly split into a training dataset; 70%(136 landslides) for training the models and the remaining 30% (58 landslides) was used for validationpurpose. Then, a total number of 14 conditioning factors, such as slope angle, slope aspect, generalcurvature, plan curvature, profile curvature, altitude, distance from rivers, distance from roads, distancefrom faults, lithology, normalized difference vegetation index (NDVI), sediment transport index (STI),stream power index (SPI), and topographic wetness index (TWI) were used in the analysis. Subsequently,landslide susceptibility maps were produced using the EBF and WoE models. Finally, the validationof landslide susceptibility map was accomplished with the area under the curve (AUC) method. Thesuccess rate curve showed that the area under the curve for EBF and WoE models were of 80.19% and80.75% accuracy, respectively. Similarly, the validation result showed that the susceptibility map usingEBF model has the prediction accuracy of 80.09%, while for WoE model, it was 79.79%. The results ofthis study showed that both landslide susceptibility maps obtained were successful and would be usefulfor regional spatial planning as well as for land cover planning.

    • Basement configuration of KG offshore basin from magnetic anomalies

      V Subrahmanyam K V Swamy Neetha Raj

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      Marine magnetic anomalies along three representative profiles falling between shelf break and continent–ocean boundary in the offshore Krishna–Godavari basin were quantitatively interpreted for understandingthe nature and structure of the magnetic basement using inversion technique. The interpretation of theanomalies shows that the magnetic basement lies deeper than the base of the sediments, i.e., acousticbasement identified by the seismic studies. This interpretation also shows that the magnetic basementis faulted along the NW–SE direction with the upthrown side lying to the north of the anomaly trendof this region. The coincidence of magnetizations observed through the present interpretation with thatof charnockites of neighbouring EGMB and onshore K–G basin areas indicates that EGMB geology(charnockites, granitic gneiss, etc.) extends up to COB in the offshore K–G basin.

    • Equatorial electrojet in the Indian region during the geomagnetic storm of 13–14 November 1998

      H Chandra R G Rastogi R K Choudhary Som Sharma

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      The geomagnetic storm of November 1998 is a unique event where IMF-Bz remained southward withvalues exceeding –15 nT for more than a day. The SYM/H index decreased from about 07 hr on 13November 1998 reaching a minimum of about –120 nT around midnight of 13–14 November 1998.Features of the equatorial electrojet in the Indian region are studied during the geomagnetic storm eventof 13–14 November 1998, based on the geomagnetic data from the chain of observatories in India. Suddennorthward turning of IMF-Bz for a very short duration around 08 hr on 13 November 1998 resultedin a small and very short duration counter electrojet. A strong (–50 nT) and a long duration counterelectrojet, right from 08 to 13 hr on 14 November 1998 was observed resulting in the absence of equatorialEs at Thumba. Absence of the equatorial ionization anomaly was also observed as seen from theionograms over Thumba and ionspheric data from Ahmedabad. The delayed effect on 14 November 1998is due to the disturbance dynamo effect.

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