Showing papers in "Journal of Earth System Science in 2015"

Trends in rainfall and rainfall-related extremes in the east coast of peninsular Malaysia

Abstract: The coastlines have been identified as the most vulnerable regions with respect to hydrological hazards as a result of climate change and variability. The east of peninsular Malaysia is not an exception for this, considering the evidence of heavy rainfall resulting in floods as an annual phenomenon and also water scarcity due to long dry spells in the region. This study examines recent trends in rainfall and rainfall- related extremes such as, maximum daily rainfall, number of rainy days, average rainfall intensity, heavy rainfall days, extreme rainfall days, and precipitation concentration index in the east coast of peninsular Malaysia. Recent 40 years (1971–2010) rainfall records from 54 stations along the east coast of peninsular Malaysia have been analyzed using the non-parametric Mann–Kendall test and the Sen’s slope method. The Monte Carlo simulation technique has been used to determine the field significance of the regional trends. The results showed that there was a substantial increase in the annual rainfall as well as the rainfall during the monsoon period. Also, there was an increase in the number of heavy rainfall days during the past four decades.

GIS-based assessment of landslide susceptibility using certainty factor and index of entropy models for the Qianyang County of Baoji city, China

Abstract: The main goal of this study is to produce landslide susceptibility maps for the Qianyang County of Baoji city, China, using both certainty factor (CF) and index of entropy (IOE) models. At first, a landslide inventory map was prepared using earlier reports and aerial photographs as well as by carrying out field surveys. A total of 81 landslide locations were detected. Out of these, 56 (70%) landslides were randomly selected as training data for building landslide susceptibility models and the remaining 25 (30%) were used for the validation purposes. Then, a total number of 15 landslide causative factors, such as slope angle, slope aspect, general curvature, plan curvature, profile curvature, altitude, distance to faults, distance to rivers, distance to roads, the sediment transport index (STI), the stream power index (SPI), the topographic wetness index (TWI), geomorphology, lithology, and rainfall, were used in the analysis. The susceptibility maps produced using CF and IOE models had five different susceptibility classes such as very low, low, moderate, high, and very high. Finally, the output maps were validated using the validation data (i.e., 30% landslide location data that was not used during the model construction), using the area under the curve (AUC) method. The ‘success rate’ curve showed that the area under the curve for CF and IOE models were 0.8433 (84.33%) and 0.8227 (82.27%) accuracy, respectively. Similarly, the validation result showed that the susceptibility map using CF model has the higher prediction accuracy of 82.32%, while for IOE model it was 80.88%. The results of this study showed that the two landslide susceptibility maps obtained were successful and can be used for preliminary land use planning and hazard mitigation purpose.

Landslide susceptibility zonation in part of Tehri reservoir region using frequency ratio, fuzzy logic and GIS

Abstract: A comprehensive study for the identification of landslide susceptible zones using landslide frequency ratio and fuzzy logic in GIS environment is presented for Tehri reservoir rim region (Uttarakhand, India). Temporal remote sensing data was used to prepare important landslide causative factor layers and landslide inventory. Primary and secondary topographic attributes namely slope, aspect, relative relief, profile curvature, topographic wetness index, and stream power index, were derived from digital elevation model. Landslide frequency ratio technique was adopted to correlate factors with landslides. Further, fuzzy logic method was applied for the integration of factors (causative factor) to map landslide susceptible zones. Normalized landslide frequency ratio value was used for the fuzzy membership function and different fuzzy operators were considered for the preparation of landslide susceptibility/hazard index map. The factors considered in this study were found to be carrying a wide range of information. Accordingly, a methodology was evolved to integrate the factors using combined fuzzy gamma and fuzzy OR operation. Fuzzy gamma integration was performed for six different gamma values (range: 0–1). Gamma value of 0.95 was selected for the preparation of final susceptibility map. Landslide susceptibility index map was divided into the following five hazard zones – very low, low, moderate, high, and very high – on the basis of natural break classification. Validation of the model was performed by using cumulative percentage curve technique. Area under curve value of cumulative percentage curve of proposed landslide susceptibility map (gamma = 0.95) was found to be 0.834 and it can be said that 83.4% accuracy was achieved by applying combined fuzzy logic and landslide frequency ratio method.

Regional biomass burning trends in India: Analysis of satellite fire data

Abstract: The results based on the analysis of satellite fire counts detected by the Along-Track Scanning Radiometer (ATSR) sensors over different regions of India during 1998–2009 have been presented. Generally, the activities of open biomass burning show large spatial and temporal variations in India. The highest and lowest values of monthly fire counts were detected during the periods of March–May and July–September, respectively over different regions of India. The activities of biomass burning in two central states of Madhya Pradesh and Maharashtra were the highest and together accounted for about 25–45% of total annual fire counts detected over India during the study period. However, in opposite phases, the rainfall and fire count data show strong seasonal variation. In addition to large regional and seasonal variations, the fire data also show significant year-to-year variation. The higher annual fire counts exceeding the mean of entire period by about 16% and 43% were detected during the two periods of 1998–2000 and 2007–2009, respectively. We have estimated normalized anomaly of annual fire count data which shows large positive departures from long-term mean for the years 1999, 2007, 2008 and 2009, while negative departures for the years 2002, 2003 and 2005. Consistently, the mixing ratio of carbon monoxide (CO) typical peaks during winter but extended to pre-monsoon season during extensive fire years. The annual data over the entire region of India show lesser positive trend of about 3% yr−1. The inter-annual variation of fire count over entire India follows the trend in the ENSO Precipitation Index (ESPI) but shows opposite trend to the multivariate ENSO Index (MEI).

Multilayer perceptron neural network for downscaling rainfall in arid region: A case study of Baluchistan, Pakistan

Abstract: Downscaling rainfall in an arid region is much challenging compared to wet region due to erratic and infrequent behaviour of rainfall in the arid region. The complexity is further aggregated due to scarcity of data in such regions. A multilayer perceptron (MLP) neural network has been proposed in the present study for the downscaling of rainfall in the data scarce arid region of Baluchistan province of Pakistan, which is considered as one of the most vulnerable areas of Pakistan to climate change. The National Center for Environmental Prediction (NCEP) reanalysis datasets from 20 grid points surrounding the study area were used to select the predictors using principal component analysis. Monthly rainfall data for the time periods 1961–1990 and 1991–2001 were used for the calibration and validation of the MLP model, respectively. The performance of the model was assessed using various statistics including mean, variance, quartiles, root mean square error (RMSE), mean bias error (MBE), coefficient of determination (R 2) and Nash–Sutcliffe efficiency (NSE). Comparisons of mean monthly time series of observed and downscaled rainfall showed good agreement during both calibration and validation periods, while the downscaling model was found to underpredict rainfall variance in both periods. Other statistical parameters also revealed good agreement between observed and downscaled rainfall during both calibration and validation periods in most of the stations.

Geochemical and isotopic signatures for the identification of seawater intrusion in an alluvial aquifer

Abstract: Seawater intrusion is one of the alarming processes that reduces the water quality and imperils the supply of freshwater in coastal aquifers. The region, north of the Chennai city, India is one such site affected by seawater intrusion. The objective of this study is to identify the extent of seawater intruded area by major geochemical and isotopic signatures. A total of 102 groundwater samples were collected and analysed for major and minor ions. Groundwater samples with electrical conductivity (EC) greater than 5000 μS/cm and a river mouth sample were analyzed for Oxygen-18 (δ 18O) and Deuterium (δ 2H) isotopes to study their importance in monitoring seawater intrusion. The molar ratio of geochemical indicators and isotopic signatures suggests an intrusion up to a distance of 13 km from the sea as on March 2012 and up to 14.7 km during May 2012.

Decline in snowfall in response to temperature in Satluj basin, western Himalaya

Abstract: Snow is an essential resource present in the Himalaya. Therefore, monitoring of the snowfall changes over a time period is important for hydrological and climatological purposes. In this study, variability of snowfall from 1976–2008 were analysed and compared with variability in temperature (T max and T min) from 1984–2008 using simple linear regression analysis and Mann–Kendall test in the Satluj Basin. The annual, seasonal, and monthly analyses of average values of snowfall and temperature (T max and T min) have been carried out. The study also consists an analysis of average values of annual snowfall and temperature over six elevation zones ( 4000 m amsl). During the study, it was observed that the snowfall exhibited declining trends in the basin. The snowfall trends are more sensitive to the climate change below an elevation of 4000 m amsl. Over the elevation zones of 3000–3500 and 4000–4500 m amsl, positive trends of mean annual values of snowfall were observed that may be due to higher precipitation as snowfall at these higher elevations. Although, both negative and positive snowfall trends were statistically insignificant, however, if this decreasing trend in snowfall continues, it may result in significant however, changes in future. Furthermore, the T min is also increasing with statistically significant positive trend at 95% confidence level for November, winter season, annually as well as for the elevation zones of 2500–3000, 3000–3500, and 3500–4000 m amsl. There are dominantly increasing trends in T max with negative trends for February, June–September, monsoon season, and for elevation zone <1500 m amls. It is important to state that in the present basin, during the months of winter season, most of the precipitation is produced as snowfall by the westerly weather disturbances. Thus, the declining nature in snowfall is concurrent with the positive trends in temperature particularly T min, therefore, reflecting that the positive trends in T min may be the dominant factor besides T max in controlling the snowfall trends. The snowfall data were also compared with SCA and this showed a highly positive correlation of 0.95% which validates the utilisation of time series of snowfall for the trend analysis.

Analysis of the accuracy of Shuttle Radar Topography Mission (SRTM) height models using International Global Navigation Satellite System Service (IGS) Network

Abstract: The Shuttle Radar Topography Mission (SRTM) carried out in February 2000 has provided near global topographic data that has been widely used in many fields of earth sciences. The mission goal of an absolute vertical accuracy within 16 m (with 90% confidence)/RMSE ∼10 m was achieved based on ground validation of SRTM data through various studies using global positioning system (GPS). We present a new and independent assessment of the vertical accuracy of both the X- and C-band SRTM datasets using data from the International GNSS Service (IGS) network of high-precision static GPS stations. These stations exist worldwide, have better spatial distribution than previous studies, have a vertical accuracy of 6 mm and constitute the most accurate ground control points (GCPs) possible on earth; these stations are used as fiducial stations to define the International Terrestrial Reference Frame (ITRF). Globally, for outlier-filtered data (135 X-band stations and 290 C-band stations), the error or difference between IGS and SRTM heights exhibits a non-normal distribution with a mean and standard error of 8.2 ± 0.7 and 6.9 ± 0.5 m for X- and C-band data, respectively. Continent-wise, Africa, Australia and North America comply with the SRTM mission absolute vertical accuracy of 16 m (with 90% confidence)/RMSE ∼10 m. However, Asia, Europe and South America have vertical errors higher than the SRTM mission goal. At stations where both the X- and C-band SRTM data were present, the root mean square error (RMSE) of both the X- and C-bands was identical at 11.5 m, indicating similar quality of both the X- and C-band SRTM data.

Evaluation of aquifer protective capacity of overburden unit and soil corrosivity in Makurdi, Benue state, Nigeria, using electrical resistivity method

Abstract: This paper presents result of 30 vertical electrical soundings carried out in Makurdi, Benue state capital, north–central Nigeria to evaluate aquifer protective capacity and soil corrosivity of overburden units in the study area. This was done using the Schlumberger electrode array to obtain the data and was modelled using computer iteration (Winresist software). The field data gives a resolution with 3–4 geoelectric layers and the observed frequencies in curve types include: 30% of KQ, 16.67% of QH, 6.67% of AA and K, 3.33% of HA, Q and A, 10% of H, KH and HK. Using the longitudinal unit conductance (S), the protective capacities of the study area were classified as 36.67% weak, 10% poor, 40% moderate, and 13.33% as good. The corrosivity ratings of the study area show that 10% is strongly corrosive, 23% moderately corrosive, 37% slightly corrosive, and 30% noncorrosive The results reasonably provide information on areas where industries can be sited and iron pipes can be laid in order to safeguard the hydrological setting for resident’s safety in the study area. Regions with moderate/good protective capacity are good sites for locating boreholes.

Influence of nutrient input on the trophic state of a tropical brackish water lagoon

Abstract: Ecosystem level changes in water quality and biotic communities in coastal lagoons have been associated with intensification of anthropogenic pressures. In light of incipient changes in Asia’s largest brackish water lagoon (Chilika, India), an examination of different dissolved nutrients distribution and phytoplankton biomass, was conducted through seasonal water quality monitoring in the year 2011. The lagoon showed both spatial and temporal variation in nutrient concentration, mostly altered by freshwater input, regulated the chlorophyll distribution as well. Dissolved inorganic N:P ratio in the lagoon showed nitrogen limitation in May and December, 2011. Chlorophyll in the lagoon varied between 3.38 and 17.66 mg m −3. Spatially, northern part of the lagoon showed higher values of DIN and chlorophyll during most part of the year, except in May, when highest DIN was recorded in the southern part. Statistical analysis revealed that dissolved NH\(_{4}^{\mathrm {+}}\)–N and urea could combinedly explain 43% of Chlorophyll-a (Chl-a) variability which was relatively higher than that explained by NO\(_{3}^{\mathrm {-}}\)–N and NO\(_{2}^{\mathrm {-}}\)–N (12.4%) in lagoon water. Trophic state index calculated for different sectors of the lagoon confirmed the inter-sectoral and inter-seasonal shift from mesotrophic to eutrophic conditions largely depending on nutrient rich freshwater input.

Assessment and mapping of flood potential in the Slănic catchment in Romania

Abstract: Flood risk assessment is an important component of risk management. Given this context, this paper aims to identify and map areas with high potential for flash-floods and flooding occurrence, at different spatial scales (from catchment to local scale), in order to estimate the flood/flooding vulnerability. The paper is based on three main methods, which were applied in the Slanic River catchment (427 km2), located in the external curvature region of the Romanian Carpathians: (i) statistical analyses; (ii) determination and mapping of some indices to assess the flash-flood and flooding potential (FFPI and respectively FPI) and (iii) hydraulic modelling. The data used mainly include hydrological statistics (maximum monthly and annual discharges, flood-related data) and spatial data on catchment geographical characteristics (hypsometry, geology, soils, land use) obtained or derived from various sources (maps, aerial images, digital databases, field measurements) which were integrated into the GIS environment. The aforementioned methods helped to (i) highlight specificities of floods in the Slanic catchment (magnitude, frequency, flood waves characteristics); (ii) identify areas with high potential for flash-floods and flooding at the catchment spatial scale; (iii) assess the structural vulnerability in the Cernatesti village, by simulating flood-prone areas for flood peaks with exceedance probability of 1%, 5% and 10%. The results could lead to a better knowledge and understanding of flood characteristics in the study area, in order to mitigate the flood risk through a more effective management, both at the catchment scale, as well as local scale (in the Cernatesti village).

Cyclone hazard proneness of districts of India

Abstract: Hazards associated with tropical cyclones (TCs) are long-duration rotatory high velocity winds, very heavy rain, and storm tide. India has a coastline of about 7516 km of which 5400 km is along the mainland. The entire coast is affected by cyclones with varying frequency and intensity. Thus classification of TC hazard proneness of the coastal districts is very essential for planning and preparedness aspects of management of TCs. So, an attempt has been made to classify TC hazard proneness of districts by adopting a hazard criteria based on frequency and intensity of cyclone, wind strength, probable maximum precipitation, and probable maximum storm surge. Ninety-six districts including 72 districts touching the coast and 24 districts not touching the coast, but lying within 100 km from the coast have been classified based on their proneness. Out of 96 districts, 12 are very highly prone, 41 are highly prone, 30 are moderately prone, and the remaining 13 districts are less prone. This classification of coastal districts based on hazard may be considered for all the required purposes including coastal zone management and planning. However, the vulnerability of the place has not been taken into consideration. Therefore, composite cyclone risk of a district, which is the product of hazard and vulnerability, needs to be assessed separately through a detailed study.

Effects of geomagnetic storm on low latitude ionospheric total electron content: A case study from Indian sector

Abstract: The effect of geomagnetic storms on low latitude ionosphere has been investigated with the help of Global Positioning System Total Electron Content (GPS-TEC) data. The investigation has been done with the aid of TEC data from the Indian equatorial region, Port Blair (PBR) and equatorial ionization anomaly region, Agartala (AGR). During the geomagnetic storms on 24th April and 15th July 2012, significant enhancement up to 150% and depression up to 72% in VTEC is observed in comparison to the normal day variation. The variations in VTEC observed from equatorial to EIA latitudes during the storm period have been explained with the help of electro-dynamic effects (prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF)) as well as mechanical effects (storm-induced equatorward neutral wind effect and thermospheric composition changes). The current study points to the fact that the electro-dynamic effect of geomagnetic storms around EIA region is more effective than at the lower latitude region. Drastic difference has been observed over equatorial region (positive storm impact) and EIA region (negative storm impact) around same longitude sector, during storm period on 24th April. This drastic change as observed in GPS-TEC on 24th April has been further confirmed by using the O/N2 ratio data from GUVI (Global Ultraviolet Imager) as well as VTEC map constructed from IGS data. The results presented in the paper are important for the application of satellite-based communication and navigational system.

Decision Support System integrated with Geographic Information System to target restoration actions in watersheds of arid environment: A case study of Hathmati watershed, Sabarkantha district, Gujarat

Abstract: Watershed morphometric analysis is important for controlling floods and planning restoration actions. The present study is focused on the identification of suitable sites for locating water harvesting structures using morphometric analysis and multi-criteria based decision support system. The Hathmati watershed of river Hathmati at Idar taluka, Sabarkantha district, Gujarat is experiencing excessive runoff and soil erosion due to high intensity rainfall. Earth observation dataset such as Digital Elevation Model and Geographic Information System are used in this study to determine the quantitative description of the basin geometry. Several morphometric parameters such as stream length, elongation ratio, bifurcation ratio, drainage density, stream frequency, texture ratio, form factor, circularity ratio, and compactness coefficient are taken into account for prioritization of Hathmati watershed. The overall analysis reveals that Hathmati comprises of 13 mini-watersheds out of which, the watershed number 2 is of utmost priority because it has the highest degradation possibilities. The final results are used to locate the sites suitable for water harvesting structures using geo-visualization technique. After all the analyses, the best possibilities of check dams in the mini-watersheds that can be used for soil and water conservation in the watershed are presented.

Performance of WRF-Chem over Indian region: Comparison with measurements

Abstract: The aerosol mass concentrations over several Indian regions have been simulated using the online chemistry transport model, WRF-Chem, for two distinct seasons of 2011, representing the pre-monsoon (May) and post-monsoon (October) periods during the Indo–US joint experiment ‘Ganges Valley Aerosol Experiment (GVAX)’. The simulated values were compared with concurrent measurements. It is found that the model systematically underestimates near-surface BC mass concentrations as well as columnar Aerosol Optical Depths (AODs) from the measurements. Examining this in the light of the model-simulated meteorological parameters, we notice the model overestimates both planetary boundary layer height (PBLH) and surface wind speeds, leading to deeper mixing and dispersion and hence lower surface concentrations of aerosols. Shortcoming in simulating rainfall pattern also has an impact through the scavenging effect. It also appears that the columnar AODs are influenced by the unrealistic emission scenarios in the model. Comparison with vertical profiles of BC obtained from aircraft-based measurements also shows a systematic underestimation by the model at all levels. It is seen that concentration of other aerosols, viz., dust and sea-salt are closely linked with meteorological conditions prevailing over the region. Dust is higher during pre-monsoon periods due to the prevalence of north-westerly winds that advect dust from deserts of west Asia into the Indo-Gangetic plain. Winds and rainfall influence sea-salt concentrations. Thus, the unrealistic simulation of wind and rainfall leads to model simulated dust and sea-salt also to deviate from the real values; which together with BC also causes underperformance of the model with regard to columnar AOD. It appears that for better simulations of aerosols over Indian region, the model needs an improvement in the simulation of the meteorology.

Climatology and trends of summer high temperature days in India during 1969–2013

Abstract: Based on the daily maximum air temperature data from 176 stations in India from 1969 to 2013, the climatological distribution of the number of days with high temperature (HT) defined as days with maximum temperature higher than 37°C during summer season (March–June) are studied. With a focus on the regional variability and long-term trends, the impacts of HT days are examined by dividing the country into six geographical regions (North, West, North-central, East, South-central and South). Although the long-term (1969–2013) climatological numbers of HT days display well-defined spatial patterns, there is clear change in climatological mean and coefficient of variation of HT days in a recent period (1991–2013). The long period trends indicate increase in summer HT days by 3%, 5%, and 18% in north, west, and south regions, respectively and decrease by 4% and 9% in north-central and east regions respectively. However, spatial variations in HT days exist across different regions in the country. The data analysis shows that 2010 was the warmest summer year and 2013 was the coolest summer year in India. Comparison of spatial distributions of trends in HT days for 1969–1990 and 1991–2013 periods reveal that there is an abrupt increase in the number of HT days over north, west and north-central regions of India probably from mid 1990s. A steep increase in summer HT days in highly populated cities of Mumbai, New Delhi, Chennai, Jaipur, and Visakhapatnam is noticed during the recent period of 1991–2013. The summer HT days over southern India indicate significant positive correlation with Nino 3.4 index for three months’ running mean (December–January–February, January–March, February–April, March–May and April–June).

Statistical downscaling and projection of future temperature and precipitation change in middle catchment of Sutlej River Basin, India

Abstract: Ensembles of two Global Climate Models (GCMs), CGCM3 and HadCM3, are used to project future maximum temperature (T Max), minimum temperature (T Min) and precipitation in a part of Sutlej River Basin, northwestern Himalayan region, India. Large scale atmospheric variables of CGCM3 and HadCM3 under different emission scenarios and the National Centre for Environmental Prediction/National Centre for Atmospheric Research reanalysis datasets are downscaled using Statistical Downscaling Model (SDSM). Variability and changes in T Max, T Min and precipitation under scenarios A1B and A2 of CGCM3 model and A2 and B2 of HadCM3 model are presented for future periods: 2020s, 2050s and 2080s. The study reveals rise in annual average T Max, T Min and precipitation under scenarios A1B and A2 for CGCM3 model as well as under A2 and B2 scenarios for HadCM3 model in 2020s, 2050s and 2080s. Increase in mean monthly T Min is also observed for all months of the year under all scenarios of both the models. This is followed by decrease in T Max during June, July August and September. However, the model projects rise in precipitation in months of July, August and September under A1B and A2 scenarios of CGCM3 model and A2 and B2 of HadCM3 model for future periods.

Deciphering groundwater quality for irrigation and domestic purposes – a case study in Suri I and II blocks, Birbhum District, West Bengal, India

Abstract: Assessment of the hydrochemical characteristics of water and aquifer hydraulic properties is important for groundwater planning and management in the study area. It is not only the basic need for human existence but also a vital input for all development activities. The present hydro-geochemical study of groundwater samples from the Suri I and II blocks of Birbhum district, West Bengal (23.76 ∘–23.99 ∘N; 87.42 ∘–87.64 ∘E) was carried out to assess their suitability for agricultural, domestic and drinking purposes. For this study, samples were collected from 26 locations during the post-monsoon and pre-monsoon sessions spanning over 2012 and 2013. Groundwater samples were analyzed for their physical and chemical properties using standard laboratory methods. Physical and chemical parameters of groundwater such as pH, electrical conductivity, total dissolved solids, Na, K, Ca, Mg, Fe, Cl, HCO3, SO4 and F were determined. Various water quality indices like SAR, SSP, PI, RSC, MAR and KR have been calculated for each water sample to identify the irrigational suitability standard. According to most of these parameters, the groundwater has been found to be well to moderately suitable for irrigation. In the post-monsoon session exceptionally high RSC values for around 80% samples indicate an alkaline hazard to the soil. The ion balance histogram for post-monsoon indicates undesirable ion balance values according to fresh water standards whereas in pre-monsoon, the samples show good ion balance in water. For determination of the drinking suitability standard of groundwater, three parameters have been considered – total hardness (TH), Piper’s trilinear diagram and water quality index study. Groundwater of the present study area has been found to be moderately-hard to hard during both sampling sessions and hence poses no health risk which could arise due to excess consumption of calcium or magnesium. Hydrogeochemical facies in the form of Piper’s trilinear diagram plot which helps in identification of the water ‘type’ which can render a particular taste or odour to water, indicates that groundwater in the study area is majorly of CaMgHCO 3 and NaHCO 3 type (fresh type) during both post-monsoon and pre-monsoon sessions barring a couple of samples which are of CaMgSO 4/CaMgClSO 4 type in pre-monsoon. Water quality index study reveals that close to 90% of the water samples are suitable for drinking during post-monsoon compared to pre-monsoon during which period only 60% of water samples fall under the suitable drinking water category. Gibbs’ diagrams, which help in identification of natural processes controlling hydrogeochemistry of groundwater indicates that for both post-monsoon and pre-monsoon sessions, the overall hydrogeochemistry of the study area is dominated by rock–water interaction processes.

Detecting, mapping and monitoring of land subsidence in Jharia Coalfield, Jharkhand, India by spaceborne differential interferometric SAR, GPS and precision levelling techniques

Abstract: The study aims at detection, mapping and monitoring of land subsidence in Jharia Coalfield, Jharkhand, India by spaceborne DInSAR, GPS and precision levelling techniques. Using multi-frequency C- and L-band DInSAR, both slowly and rapidly subsiding areas were identified and DInSAR-based subsidence maps were prepared. C-band DInSAR was found useful for detection of slowly subsiding areas whereas L-band DInSAR for rapidly subsiding and/or adverse land cover areas. Due to dynamic nature of mining and adverse land cover, temporal decorrelation poses a serious problem particularly in C-band DInSAR. Specially designed InSAR coherence guided adaptive filtering was found useful to highlight the deformation fringes. Collateral GPS and levelling observations were conducted in three test sites to validate DInSAR measurements and to determine the net displacement vectors. We observed an appreciable horizontal displacement component of land subsidence in all the test sites. For comparison of results, we calculated InSAR coherence weighted LOS displacement rates from the unwrapped differential interferograms of smaller spatial subsets and LOS projected ground-based displacement rates in three test sites. We found good agreement between DInSAR and ground-based measurements except for C-band observation in Dobari test site primarily due to large difference in observation periods and temporally inconsistent land subsidence. Collateral spaceborne and ground-based observations were also found useful for characterization of subsidence phenomena to determine net displacement vector and horizontal displacement component. In coal mining areas with spatially scattered and temporally irregular land subsidence phenomena, the adopted methodology can be used successfully for detection, mapping and monitoring of the subsiding areas vulnerable to future collapse. This will facilitate efficient planning and designing of surface infrastructures and other developmental structures in the mining areas and mitigation management of subsidence induced hazards.

Water use efficiency of net primary production in global terrestrial ecosystems

Abstract: The carbon and water cycles of terrestrial ecosystems, which are strongly coupled via water use efficiency (WUE), are influenced by global climate change. To explore the relationship between the carbon and water cycles and predict the effect of climate change on terrestrial ecosystems, it is necessary to study the WUE in global terrestrial ecosystems. In this study, the 13-year WUE (i.e., net primary production (NPP)/evapotranspiration (ET)) of global terrestrial ecosystems was calculated based on the Moderate Resolution Imaging Spectro-radiometer (MODIS) NPP (MOD17A3) and ET (MOD16A3) products from 2000 to 2012. The results indicate that the annual average WUE decreased but not significantly, and the 13-year mean value was 868.88 mg C m −2 mm −1. The variation trend of WUE value for each pixel differed greatly across the terrestrial ecosystems. A significant variation (P Oceania (1084.46 mg C m −2 mm −1)> Africa (893.51 mg C m −2 mm −1)> South America (893.07 mg C m −2 mm −1)> North America (870.79 mg C m −2 mm −1)> Asia (738.98 mg C m −2 mm −1) and warm temperate climates (1094 mg C m −2 mm −1)> snowy climates (862 mg C m −2 mm −1)> arid climates (785 mg C m −2 mm −1)> equatorial climates (732 mg C m −2 mm −1)> polar climates (435 mg C m −2 mm −1). Based on the WUE value and the present or future rainfall, the maximum carbon that fixed in one region may be theoretically calculated. Also, under the background of global climatic change, WUE may be regarded as an important reference for allotting CO 2 emissions offsets and carbon transactions.

Evaluating the influence of spatial resolutions of DEM on watershed runoff and sediment yield using SWAT

Abstract: Digital elevation model (DEM) of a watershed forms key basis for hydrologic modelling and its resolution plays a key role in accurate prediction of various hydrological processes. This study appraises the effect of different DEMs with varied spatial resolutions (namely TOPO 20 m, CARTO 30 m, ASTER 30 m, SRTM 90 m, GEO-AUS 500 m and USGS 1000 m) on hydrological response of watershed using Soil and Water Assessment Tool (SWAT) and applied for a case study of Kaddam watershed in India for estimating runoff and sediment yield. From the results of case study, it was observed that reach lengths, reach slopes, minimum and maximum elevations, sub-watershed areas, land use mapping areas within the sub-watershed and number of HRUs varied substantially due to DEM resolutions, and consequently resulted in a considerable variability in estimated daily runoff and sediment yields. It was also observed that, daily runoff values have increased (decreased) on low (high) rainy days respectively with coarser resolution of DEM. The daily sediment yield values from each sub-watershed decreased with coarser resolution of the DEM. The study found that the performance of SWAT model prediction was not influenced much for finer resolution DEMs up to 90 m for estimation of runoff, but it certainly influenced the estimation of sediment yields. The DEMs of TOPO 20 m and CARTO 30 m provided better estimates of sub-watershed areas, runoff and sediment yield values over other DEMs.

Statistical analysis of long term spatial and temporal trends of temperature parameters over Sutlej river basin, India

Abstract: The annual and seasonal trend analysis of different surface temperature parameters (average, maximum, minimum and diurnal temperature range) has been done for historical (1971–2005) and future periods (2011–2099) in the middle catchment of Sutlej river basin, India. The future time series of temperature data has been generated through statistical downscaling from large scale predictors of CGCM3 and HadCM3 models under A2 scenario. Modified Mann–Kendall test and Cumulative Sum (CUSUM) chart have been used for detecting trend and sequential shift in time series of temperature parameters. The results of annual trend analysis for period of 1971–2005 show increasing as well as decreasing trends in average (T Mean), maximum (T Max), minimum (T Min) temperature and increasing trends in Diurnal Temperature Range (DTR) at different stations. But the annual trend analysis of downscaled data has revealed statistically significant (95% confidence level) rising trends in T Mean, T Max, T Min and falling trend in DTR for the period 2011–2099. The decreasing trend in DTR is due to higher rate of increase in T Min compared to T Max.

Characteristics of surface wind structure of tropical cyclones over the north Indian Ocean

Abstract: Tropical cyclone (TC) wind field monitoring and forecast are important for mariners, ships on sea and modelling group for creation of synthetic vortex, and storm surge and coastal inundation forecasting. Among others, a multi-platform satellite surface wind analysis developed by Co-operative Institute for Research in the Atmosphere (CIRA), USA for the TCs are referred by India Meteorological Department for surface wind field monitoring of TC. Hence, a study has been undertaken to analyze the characteristics of surface wind distribution and hence the structure of TC based on the real time data available from CIRA during 2007–2013. The study includes 19 TCs over the Bay of Bengal (BOB) and six over Arabian Sea (AS). The maximum radial extent of winds reaching threshold values of 34(17), 50(26) and 64(33) knot (ms−1) in each of the four geographical quadrants has been segregated with respect to season of formation, basin of formation and intensity of TC for analysis. The objective is to develop a reference surface wind structure of TC and examine its validity with respect to physical processes. The size of outer core (34(17) knot (ms−1) wind radial extension) as well as inner core (50(26) and 64(33) knot (ms−1) wind radial extension) increases significantly with increase in intensification of TC over BOB during both pre-monsoon and post-monsoon seasons and over AS during pre-monsoon season. The outer core of winds in TCs over the BOB is asymmetric in both pre-monsoon and post-monsoon seasons and for all categories of intensity of TCs. On the other hand, the asymmetry in inner core winds is significantly less. There is also no asymmetry in radial wind extension over the AS during both the seasons, except in case of outer core wind radial extension of VSCS during pre-monsoon season. The low level environment like enhanced cross equatorial flow, lower/middle level relative humidity, vertical wind shear and proximity of TC to the land surface are the determining factors for the size and asymmetry of TCs over the NIO.

Evaluation of official tropical cyclone landfall forecast issued by India Meteorological Department

Abstract: India Meteorological Department (IMD) introduced the objective tropical cyclone (TC) track forecast valid for next 24 hrs over the North Indian Ocean (NIO) in 2003. It further extended the validity period up to 72 hrs in 2009. Here an attempt is made to evaluate the TC landfall forecast issued by IMD during 2003–2013 (11 years) by calculating the landfall point forecast error (LPE) and landfall time forecast error (LTE). The average LPE is about 67, 95, and 124 km and LTE is about 4, 7, and 2 hrs, respectively for 24, 48, and 72-hr forecasts over the NIO as a whole during 2009–2013. The accuracy of TC landfall forecast has been analysed with respect to basin of formation (Bay of Bengal, Arabian Sea, and NIO as a whole), specific regions of landfall, season of formation (pre-monsoon and post-monsoon seasons), intensity of TCs (cyclonic storm (CS), and severe cyclonic storm (SCS) or higher intensities) at the time of initiation of forecast and type of track of TCs (climatological/straight moving and recurving/looping type). The LPE is less over the BOB than over the AS for all forecast lengths up to 72 hrs. Similarly, the LPE is less during the post-monsoon season than during pre-monsoon season. The LPEs are less for climatologically moving/straight moving TCs than for the recurving/looping TCs. The LPE over the NIO has decreased at the rate of about 14.5 km/year during 2003–2013 for 24-hr forecasts. The LTE does not show any significant improvement for 24-hr forecast during the same period. There is significant decrease in LPE and LTE during 2009–2013 compared to 2003–2008 due to the modernisation programme of IMD. The 24-hr LPE and LTE have decreased from 157.5 to 66.5 km and 7.8 to 4.1 hrs, respectively. However, there is still scope for further reduction in 48 and 72-hr forecast errors over the NIO to about 50 and 100 km respectively based on the latest technology including aircraft reconnaissance, deployment of buoys, and assimilation of more observational data from satellite and Doppler weather radars, etc., in the numerical weather prediction (NWP) models during the next five years.

Variability in stratification and flushing times of the Gautami–Godavari estuary, India

Abstract: In order to examine the influence of forcing (river flow and tides) and anthropogenic activities (dredging and dam regulation) on stratification, a study was conducted over a period of 19 months (June 2008–December 2009) in the Gautami–Godavari estuary (G–GE) during spring and neap tide periods covering entire spectrum of discharge over a distance of 36 km from the mouth. The bathymetry of the estuary was recently changed due to dredging of ∼20 km of the estuary from the mouth for transportation of barges. This significantly changed the mean depth and salinity of the estuary from its earlier state. The variations in the distribution of salinity in the Godavari estuary are driven by river discharge during wet period (June–November) and tides during dry period (December–May). The weak stratification was observed during high discharge (July–August) and no discharge (January–June) periods associated with dominant fresh water and marine water respectively. The strong stratification was developed associated with decrease in discharge during moderate discharge period (October–December). Relatively stronger stratification was noticed during neap than spring tides. The 15 psu isohaline was observed to have migrated ∼2–3 km more towards upper estuary during spring than neap tide suggesting more salt enters during former than latter period. Total salt content was inversely correlated with river discharge and higher salt of about 400×106 m3 psu was observed during spring than neap tide. Flushing times varied between less than a day and more than a month during peak and no discharge periods respectively with lower times during spring than neap tide. The flushing times are controlled by river discharge during high discharge period, tides during dry period and both (river discharge and tides) under moderate discharge period. This study suggests that modification of discharge, either natural due to weak monsoon, or artificial such as dam constructions and re-routing the river flow, may have significant impact on the stratification and biogeochemistry of the Godavari estuary.

Numerical simulation of an intense precipitation event over Rudraprayag in the central Himalayas during 13–14 September 2012

Abstract: A recent heavy precipitation event on 13 September 2012 and the associated landslide on 14 September 2012 is one of the most severe calamities that occurred over the Rudraprayag region in Uttarakhand, India. This heavy precipitation event is also emblematic of the natural hazards occuring in the Himalayan region. Study objectives are to present dynamical fields associated with this event, and understand the processes related to the severe storm event, using the Weather Research and Forecasting (WRF ver 3.4) model. A triple-nested WRF model is configured over the Uttarakhand region centered over Ukhimath (30∘30′N; 79 ∘15′E), where the heavy precipitation event is reported. Model simulation of the intense storm on 13 September 2012 is with parameterized and then with explicit convection are examined for the 3 km grid spacing domain. The event was better simulated without the consideration of convection parameterization for the innermost domain. The role of steep orography forcings is notable in rapid dynamical lifting as revealed by the positive vorticity and high reflectivity values and the intensification of the monsoonal storm. Incursion of moist air, in the lower levels, converges at the foothills of the mountains and rise along the orography to form the updraft zone of the storm. Such rapid unstable ascent leads to deep convection and increases the condensation rate of the water vapour forming clouds at a swift rate. This culminates into high intensity precipitation which leads to high amount of surface runoff over regions of susceptible geomorphology causing the landslide. Even for this intense and potentially unsual rainfall event, the processes involved appear to be the ‘classic’ enhanced convective activity by orographic lifting of the moist air, as an important driver of the event.

Characteristics of water isotopes and hydrograph separation during the spring flood period in Yushugou River basin, Eastern Tianshans, China

Abstract: Many of the river basins in northwest China receive water from melting glaciers and snow in addition to groundwater. This region has experienced a significant change in glacier and snowpack volume over the past decade altering hydrology. Quantifying changes in water resources is vital for developing sustainable strategies in the region. During 2013, a water-isotope source apportionment study was conducted during the spring flood in the Yushugou River basin, northwestern China. The study found significant differences in water isotopes between river water, snowmelt water, and groundwater. During the study period, the isotopic composition of groundwater remained relatively stable. This stability suggests that the groundwater recharge rate has not been significantly impacted by recent hydro-climatic variability. The river water flow rate and water δ 18O displayed an inverse relationship. This relationship is indicative of snowmelt water injection. The relative contribution of the two sources was estimated using a two-component isotope hydrograph separation. The contribution of snowmelt water and groundwater to Yushugou River were ∼63% and ∼37%, respectively. From the study, we conclude that snowmelt water is the dominant water source to the basin during the spring melt period.

Morphotectonic analysis, structural evolution/pattern of a contractional ridge: Giouchtas Mt., Central Crete, Greece

Abstract: The Giouchtas Mountain is situated south of Heraklion, Central Crete. It is a N–S trending morphological asymmetric ridge with a steep western slope, whilst its eastern slope is characterized by a smoother relief, composed of Mesozoic limestone and Eocene–lower Oligocene flysch of the Gavrovo–Tripolis zone. The present study focusses on the structural pattern and development of Giouchtas Mountain. Morphotectonic analyses in combination with field mapping and tectonic analysis were performed for this purpose. GIS techniques were used for mapping the spatial distribution of the geological features on the topographic relief of the area. Geomorphic indices, used in the present study, are the mountain front sinuosity index (Smf) and the valley floor/width ratio index (Vf). Based on Smf and Vf values, it is implied that this area can be assigned to a tectonic class I, corresponding to higher tectonic activity. However, spatial variations of the tectonic activity along the segmented fronts point to a general trend of increasing activity towards the north and especially, northeast. The model of this possibly active structural feature corresponds to a compressional mechanism followed by an earliest Mid. Miocene to Holocene late-stage deformation related to extensional faulting.

Analysis of drought areas in northern Algeria using Markov chains

Abstract: The present work studies the trends in drought in northern Algeria. This region was marked by a severe, wide-ranging and persistent drought due to its extraordinary rainfall deficit. In this study, drought classes are identified using SPI (standardized precipitation index) values. A Markovian approach is adopted to discern the probabilistic behaviour of the time series of the drought. Thus, a transition probability matrix is constructed from drought distribution maps. The trends in changes in drought types and the distribution area are analyzed. The results show that the probability of class severe/extreme drought increases considerably rising from the probability of 0.2650 in 2005 to a stable probability of 0.5756 in 2041.

Physico-chemical characteristics of Jharkhand and West Bengal thermal springs along SONATA mega lineament, India

Abstract: The chemical and isotopic compositions of thermal springs located along the Son–Narmada–Tapti (SONATA) mega lineament in central India have been investigated. The issuing temperatures of the thermal waters vary from 31° to 89°C for the thermal springs and 24° to 25°C for the cold springs. These thermal springs are located on the Archean Chotanagpur Gneissic Complex (CGC) in the eastern part of peninsular India. The thermal springs are mostly alkaline in nature with pH varying from 7.5 to 9.5. Piper diagram suggests that the chemistry of the thermal waters is compatible with the granitic host rocks through which the waters circulate. Mineral saturation index suggests that the thermal waters are saturated with cristobalite and quartz at lower temperatures (less than ∼130 to 150°C), and calcite and forsterite at higher temperatures (∼160° to 250°C). The estimated reservoir temperature based on chemical geothermometers is in the range of 132°–265°C, which favours a medium enthalpy geothermal system. Oxygen isotope fractionation of Bakreswar and Tantloi thermal springs highlights a higher reservoir temperature than estimated by chemical geothermometer. Positive gravity anomalies over Bakreswar and Tantloi areas strongly suggest a basement/mantle upliftment or mafic intrusion which could account for the heat source close to the surface. However, the large negative gravity anomaly depression around the Surajkund and Katkamsandi thermal springs indicates presence of deep seated faults.