Semi-arid Region In Southern India Research Articles

Assessing the impacts of climate and land cover change on groundwater recharge in a semi-arid region of Southern India

Assessing the impacts of climate and land cover change on groundwater recharge in a semi-arid region of Southern India

Groundwater irrigation reduces overall poverty but increases socioeconomic vulnerability in a semiarid region of southern India

The development of irrigation is generally considered an efficient way to reduce poverty in rural areas, although its impact on the inequality between farmers is more debated. In fact, assessing the impact of water management on different categories of farmers requires resituating it within the different dimensions of the local socio-technical context. We tested this hypothesis in a semi-arid area in Karnataka, South India, where groundwater irrigation was introduced five decades ago. Using the conceptual framework of comparative agriculture, based on farmers’ interviews, we built a farm typology, traced the trajectories of farm types over the last decades and assessed their current technical and economic performances. Our results show that the differentiation of farm trajectories since the 1950s has been linked with the development of groundwater irrigation, interplaying with their initial assets, and the evolution of the national and local contexts. We highlight the mechanisms by which irrigation indeed reduces poverty but engenders fragilities, particularly for poor households, whose situation was aggravated by the depletion of water resources over the last two decades. Finally, this extensive understanding of the agrarian context allowed us to formulate and assess the potential of different ways forward, including irrigation technology, change in cropping or livestock systems, land tenure, and value added distribution. As such, this analysis would be of major interest to policy makers involved in reforming the agricultural context for better agricultural water management.

Evaluation of groundwater quality and its suitability for drinking purposes in semi-arid region of Southern India: an application of GIS

In the present study, the quality of groundwater for drinking purposes was evaluated. The following parameters were analyzed using American Public Health Association standard method: pH, total hardness (TH), total dissolved solids (TDS), electrical conductivity (EC), bicarbonate (HCO3 −), chloride (Cl−), sulphate (SO4 2−), fluoride (F−), calcium (Ca2+), magnesium (Mg2+), sodium (Na+) and potassium (K+). These values were compared with limits recommended by the World Health Organization (WHO) and the Bureau of Indian Standards (BIS) for drinking purposes. The cation and anion dominance of the study region groundwater samples were Na+ > Ca2+ > Mg2+ > K+ and HCO3 − > Cl− > SO4 2− > F−, respectively. Bicarbonate was the dominant anion and Na+ was identified as the dominant cation in the groundwater of the study region. The Na+ and Cl− concentration of 43% and 37% of groundwater samples were found to be more than the acceptable limit of WHO in the study region. Most of the groundwater samples in the study region were categorized as a very hard category. The groundwater was highly affected by the fluoride and about 60% of groundwater samples were unfit for drinking purposes in the study region.

Identification of artificial groundwater recharge zones in semi-arid region of southern India using geospatial and integrated decision-making approaches

The present study integrates various decision-making methods viz. Fuzzy Logic (FL), Frequency Ratio (FR), Analytical Hierarchy Process (AHP) to delineate the artificial groundwater recharge zones (AGRZs) in semi-arid region of south India. Eight criterions used in this process, including lithology, soil types, lineament density (LD), drainage density (DD), vadose zone (VZ), rainfall, land use/ land cover (LULC), and slope. All of these criteria and their sub-criteria used to derive weights for different thematic layers and combined using a geospatial method to classify AGRZs. The resultant map was categorised into five classes: very poor, poor, moderate, good and very good. The FL, AHP, FR, and integrated approaches were validated against groundwater fluctuation data using receiver operating characteristic (ROC) and field AUC [Area Under the Curve] approaches, showed an accuracy of 72%, 76% and 78% and 82%. As a result, the output of the integrated models outperforms that of the FR, FL and AHP models. Fuzzy reasoning and AHP methods rely on assigning a relative score based on the significance of the variables, which necessitates extensive knowledge of the criterions. FR, on the other hand, is simpler and more reliable since it does not rely on user-based scoring for the various criterions. The results of this study can be useful for decision makers responsible for the sustainable management of groundwater resources.

Assessment of precipitation trends and its implications in the semi-arid region of Southern India

Rainfall is a complex meteorological phenomenon with high spatio-temporal variability. These variations in hydrologic time series can be better analyzed using homogeneity and trend tests. In this paper, three homogeneity tests were applied to the annual rainfall series of 1980–2013 from 30 raingauge stations over the study area. The rainfall stations with homogeneous time series were subjected to cluster analysis (Agglomerative Hierarchical Clustering technique) and thereafter traditional trend tests (Mann-Kendall test and Spearman Rank-order Correlation test) and one emerging trend test (called ‘Innovative Trend test’) were applied to individual clusters. Based on the homogeneity test results, 27 rainfall stations with homogeneous time series were classified under six clusters. The results of the trend analysis revealed that a distinct pattern of increasing (decreasing) rainfall trend exists in the northern (southern) part of the study area. Although the traditional tests detected insignificant trends, the Innovative Trend (IT) test indicated the trends to be significant in all the clusters. However, the magnitude of trends detected by the traditional trend tests and non-traditional trend tests is similar for all the clusters. It is concluded that the emerging IT test is highly sensitive to the changes in the rainfall time series. The findings of this study suggest that the orography, population density, industrialization and agricultural intensity lead to a precipitation gradient in the study area.

Isotopic differentiation of groundwater recharge processes in a semi-arid region of southern India

Isotopic differentiation of groundwater recharge processes in a semi-arid region of southern India

Water management using traditional tank cascade systems: a case study of semi-arid region of Southern India

Most arid and semi-arid regions of the Southern-Indian peninsula experience frequent drought. To combat this, historically many water recharge structures, such as tank cascade systems, have been constructed. However, in recent years, performance of these tanks, especially for irrigation and groundwater recharge, is limited due to impacts of external factors that are not scientifically understood. This study, for the first time, aimed to explore spatio-temporal variation of water mass balance components and their impact on the Vandiyur tank cascade system (VTCS) in the city of Madurai, India. Study estimated water mass balance components for rural, peri-urban, and urban catchments across VTCS. Catchment-specific algorithms and water budget equation were used to estimate the volume of hydrological parameters. Additionally, land use/land cover maps were developed to understand the significance of using a water balance approach in understanding the behavior of hydrological components governing the water budget of a catchment. Results indicated a rapid increase in the urban area, up to 300%, in peri-urban and urban regions. Urbanization was considered the primary cause of high catchment runoff (40–60% of rainfall). Due to this, seasonal water availability within each tank across catchment was observed inconsistent (0–15%), wherein summer recorded approximately the least tank storage (0–8%). In general, study provided an approach for a practical, water‐focused application demonstrating how the principles of mass balance can help to foster robust water accounting, monitoring, and management. It further emphasized the use of a water balance approach in identifying vulnerable catchments for appropriate tank-rehabilitation-based interventions.

The Impact of Lockdown on eBC Mass Concentration over a Semi-arid Region in Southern India: Ground Observation and Model Simulations

ABSTRACT In the present study, we focused on the impact of lockdown on black carbon (eBC) mass concentrations and their associated radiative implications from 01st March to 30th June 2020, over a semi-arid station, i.e., in the district of Anantapur in Southern India. The mean eBC mass concentration was observed before lockdown (01st–24th March 2020) and during the lockdown (25th March–30th June 2020) period and was about 1.74 ± 0.36 and 1.11 ± 0.14 µg m–3, respectively. The sharp decrease (~35%) of eBC mass concentration observed during the lockdown (LD) period as compared with before lockdown (BLD) period, was mainly due to the reduction of anthropogenic activities and meteorology. Furthermore, during the entire LD period, the net composite forcing at the top of the atmosphere (TOA) and at the surface (SUR) varied from –4.52 to –6.19 Wm–2 and –22.91 to –29.35 Wm–2, respectively, whereas the net forcing in the atmosphere (ATM) varied from 17.27 to 23.16 Wm–2. Interestingly, the amount of energy trapped in the atmosphere due to eBC is 11.19 Wm–2 before LD and 8.56 Wm–2 during LD. It is concluded that eBC contributes almost 43–50% to the composite forcing. As a result, the eBC atmospheric heating rate decreased significantly (25%) when compared to before lockdown days to lockdown days.

Long-term (2008–2017) analysis of atmospheric composite aerosol and black carbon radiative forcing over a semi-arid region in southern India: Model results and ground measurement

To achieve an in-depth understanding of radiative forcing due to aerosols is a crucial challenge for climate change studies. The first-ever long-term measurement of direct shortwave composite and black carbon aerosol radiative properties over a semi-arid region, Anantapur, in southern India is presented. Long-term variations in Aerosol Optical Depth (AOD) and Black Carbon (BC) mass concentration from December 2007 to November 2017 are discussed with specific emphasis on intra-seasonal variation in aerosol optical properties, meteorology, transport pathways, and their implications for direct short wave radiative forcing over Anantapur. The intra-seasonal mean AOD showed strong seasonal dependence with the highest (0.47 ± 0.03) during summer and lowest (0.28 ± 0.03) during the monsoon. Meanwhile, the intra-seasonal mean (±σ) BC mass concentration was about 3.57 ± 0.45, 2.60 ± 0.58, 1.22 ± 0.18 and 2.24 ± 0.28 μg m−3 during winter, summer, monsoon and post-monsoon respectively. Furthermore, there is an obvious temporal variation in intra-seasonal BC mass concentration during the dry season (winter and summer). To be more specific, the intra-seasonal mean (±σ) BC mass concentration before 2012 (after 2012) during the dry season was about 3.37 ± 0.7 μg m−3 (2.80 ± 0.58 μg m−3), respectively. Concentration weighted trajectory analyses (CWT) revealed that the air masses originated from the continental and polluted environments located in the central and northern parts of India (except monsoon), in regulating BC mass concentration over measurement location. Further, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) derived aerosol vertical extinction profiles (532 nm) showed that majority aerosols (>250 Mm−1) are confined within 2 km from the surface during winter while in summer particles are distributed throughout the profile (~6 km) with extinction coefficient varying between 200 and 250 Mm−1. The Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model estimated intra-seasonal mean direct shortwave composite aerosol radiative forcing (DARF) in the atmosphere (ATM) was about 31.13 ± 3.36, 34.82 ± 3.89, 17.10 ± 1.15, and 17.44 ± 1.81 Wm-2 during winter, summer, monsoon and post-monsoon, respectively. The positive signs of ATM forcing in all seasons indicate a warming of the atmosphere, and the corresponding heating rate was around a factor of two higher during the dry season (0.92 ± 0.12 Kday−1) than the wet season (monsoon and post-monsoon) (0.49 ± 0.04 Kday−1). The intra-seasonal mean BC forcing in ATM before 2012 (After 2012) during the dry season was about 24.14 ± 2.85Wm-2(20.09 ± 2.59Wm-2), respectively. The contribution of BC alone to the composite forcing during the study period over the station was ~68%. These findings would be helpful for regional climate studies and making air pollution control policy over the region.

Appraisal of subsurface hydrogeochemical processes in a geologically heterogeneous semi-arid region of south India based on mass transfer and fuzzy comprehensive modeling.

The main aim of the present study was to examine the quality of the groundwater and decipher the sources of groundwater fluoride through mass balance modeling based on fluoride exposure in a geologically heterogeneous semi-arid region of southern India. This was achieved by hydrogeochemical analysis, graphical methods, and mass transfer modeling approaches. Fuzzy comprehensive technique was applied to evaluate the quality of groundwater for groundwater management. In this regard, 61 groundwater samples were obtained from open wells and bore wells and analyzed for different physicochemical parameters. The major cation and anion abundances follow the order Na+ > Ca2+ > Mg2+ > K+ and Cl- > HCO3- > SO42- > NO3- > PO43-. About 88.4% and 34.4% of the total water samples were dominated with Na+ and Cl- ions in this region, respectively. The fluoride level in groundwater ranged from 0.10 to 3.30mg/l with a mean value of 1.04mg/l. Nearly 25% of the groundwater samples collected from 15 villages showed fluoride concentrations exceeding the maximum permissible limit of 1.5mg/l as per the World Health Organization recommendations for human intake. More than 85% of the samples fell under strong acid (Cl- and SO42-) type. The amount of groundwater salinization in this region was 70.5% since the Revelle index (RI) was excess in the groundwater samples (RI > 0.5meq/l). Silicate weathering, cation exchange, and gypsum dissolution were the dominant geogenic processes in the aquifer system influencing groundwater chemistry and nullified the possibility of carbonate dissolution. Saturation indices revealed the contribution of sequestration of CaCO3 in F- enrichment. Total dissolved solids showed strong positive correlations with Na+, Ca2+, Mg2+, Cl-, SO42- and NO3- indicating the contribution of anthropogenic inputs to groundwater chemistry in addition to geogenic sources. The results of the fuzzy comprehensive method indicated that 33% of the groundwater samples fell under fair water type, 2% and 11% of the samples fell under poor and very poor quality water types, respectively. Therefore, this work will be helpful for the decision-makers to plan for the sustainable management of groundwater resources.

Modelling the daily reference evapotranspiration in semi-arid region of South India: A case study comparing ANFIS and empirical models

The estimation of evapotranspiration (ETo) is one of the main tools for the control of crop growth and to make a rational use of water resources. To estimate this parameter accurately, it is necessary to have a daily measurement of four meteorological variables, these are: temperature, solar radiation, relative humidity and wind speed. It is not always possible to count on all the variables, that is why there are empirical methods that use a limited number of variables that make an approximate estimate of the ETo value. Each of these models are applicable to different regions with completely different climates. In this paper, a study has been carried out to define the model of ETo estimation that best adapts to the semi-arid region in South India. Two different datasets for the same period from different meteorological stations were used. In addition to the empirical methods for estimating ETo, computer models ANFIS (Adaptive Neuro-Fuzzy Inference System) were implemented. These models consist in the future estimation of a certain parameter by using current variables and a history of variables and past results. The results of this work show that ANFIS 11 model makes the best estimate with RMSD = 0.002 and r = 0.999. The RITCHIE method is the most suitable empirical model for this region, which reaches RMSD = 0.507 and r = 0.851. In addition, ranking of equations is elaborated for both datasets for daily estimates of ETo. Finally, comparison is made with the results for each case and thus confirm or reject the convenience of one model over the rest. To achieve this, a series of statistical indicators were used: Index of agreement (d), MAE (Mean absolute error), SEE (Standard error of estimate) and RMSD (Root mean square difference). Moreover, a sensitivity analysis was performed in order to compare and show the stability of the best models when an error is introduced within the input parameters. In this case, the empirical models demonstrate a better performance than the ANFIS models. This work demonstrates that the Ritchie method is a good estimator of the ETo value for a semi-arid region in southern India. In addition, the results of the ANFIS models are promising and could be used as estimation methods.

Identification of groundwater recharge-based potential rainwater harvesting sites for sustainable development of a semiarid region of southern India using geospatial, AHP, and SCS-CN approach

Groundwater recharge-based rainwater harvesting (RWH) is a standout among the most capable structures to reduce water deficit issues and to build the accessibility of water for sustainable development in the semiarid regions because of absence of precipitation and flighty precipitation patterns. The delineation of potential recharge zone (PRZ) with RWH and selection of sites cause a greater dispute for the water stakeholders because of deficient framework. The essential thematic layer such as land use/land cover, soil, geology, vadose zone, drainage density, slope, and runoff were used for delineation of PRZ and RWH sites. Analytical hierarchical process (AHP) was carried out by assigning different weights to different thematic layers to determining the PRZ and RWH sites. The present study endeavours to decide the suitable areas for RWH using Soil Conservation Service curve number (SCS-CN) based on surface runoff with geospatial techniques. The enlargement of water asset is proposed by the development of RWH structures such as farm pond (FP), percolation tank (PT), check dam (CD), and gully plug (GP) having 73.53% (358.08 km2) appropriate for FP, 8.62% (42 km2) reasonable for PT, 17.48% (85.16 km2) reasonable for CD, and 0.35% (1.71 km2) for GP of the present study region. Based on integrated mission of sustainable development specification, 20 PT, 11 FP, and 4 CD were identified having 85%, 90%, and 100% accuracy in agreement between existing structures and predicted potential site. The present study approach demonstrates the higher accuracy for identification of RWH at any scale with sustainable water resources development.

Effect of climatic variability and weather factors on development of tomato early blight in a hot semi-arid region of Southern India

Effect of climatic variability and weather factors on development of tomato early blight in a hot semi-arid region of Southern India

Modeling and assessing land-use and hydrological regimes to future land-use scenario for sustainable watershed management in a semi-arid region of southern India

The present study investigates impact of land use land cover (LULC) change and water harvesting interventions in Kanva watershed, a rural catchment in Kaveri basin, located in semi arid region of southern India. Remote sensing data and Soil and Water assessment Tool hydrological model was used to assess changes in total water yield, groundwater recharge, percolation and evapotranspiration. Post classification change detection technique was used for LULC change analysis in 1992, 2001, 2008 and 2014. Modelling was also performed to assess potential impact of LULC using predicted land use scenario of 2022. A comparison between 1995–2003 (pre-watershed management) and 2004–2016 (post-watershed management) simulations indicated an increase of 1.01%, 4.65% and 1.74% in average runoff coefficient, groundwater recharge coefficient and percolation coefficient respectively, and decrease in evaporation coefficient by 0.51%. The results showed that LULC changes and water harvesting accounted for a difference in hydrological components between these two periods. Scenario analyses were performed for different adoption rates of rain water harvesting (RWH) interventions in sub-watersheds of Kanva watershed and its impact on hydrological parameters, especially on total water yield was identified. The analysis indicated that average runoff coefficient was 9.16% during pre-watershed period and 9.25% during post-watershed period. Further up-scaling of RWH would reduce the flow and runoff coefficient may decrease to 6.07% if RWH is adopted in whole of Kanva watershed. The results suggested that if extensive RWH is carried out in the Kanva watershed, it would result in unsustainable water management due to reduced flow downstream. The study found that the sustainability of watersheds in arid and semi-arid regions is very important given the uncertainties in future hydrologic regimes due to changes in land cover and changes in extreme rainfall patterns thus requiring suitable management interventions.

Characterization of aerosol optical properties and model computed radiative forcing over a semi-arid region, Kadapa in India

In this paper, we present the optical and radiative properties of aerosols for the first time measured at Yogi Vemana University (YVU) campus (14.47°N, 78.82°E, 138 m above sea level), Kadapa, a semi-arid region in southern India during December 2013–February 2015. The collocated measurements of aerosol optical depth (AOD) and black carbon (BC) mass concentration are carried out at Kadapa using the ten channels Multi-Wavelength solar Radiometer (MWR) and seven wavelengths Aethalometer, respectively. This work mainly focused on studying the temporal and spectral behavior of aerosol properties, and their implications to the aerosol direct radiative forcing (ADRF). The respective seasonal mean values of AOD at 500 nm were found to be 0.33 ± 0.01, 0.46 ± 0.05, 0.27 ± 0.02 and 0.37 ± 0.06 during the winter, summer, monsoon and post-monsoon, with an annual mean of 0.38 ± 0.18. It is revealed that the Ångström exponent (AE or α380–850) value was observed to be maximum (minimum) in March (July) with 1.75 ± 0.19 (0.65 ± 0.14) indicates a predominance of fine (coarse) mode aerosols. Added to this, the diurnal variations of BC mass concentration exhibited two maxima with peaks occurred during 07:00–08:00 h and 20:00–21:00 h local time (LT), and a minimum of the afternoon hours around 13:00–16:00 h LT. Further, the AOD-AE relationship was investigated over Kadapa, and the results conclude that the urban-industrial/biomass burning (UI/BB) type aerosols are more dominated during the study period. The OPAC model retrieved single scattering albedo (SSA) at 500 nm was found to vary between 0.83 and 0.92 with relatively lower values during winter, suggest an increase in absorbing type aerosols produced from anthropogenic activities. The SBDART model computed seasonal averaged ADRF within the atmosphere (ADRFATM) was found to be 26.7 ± 2.3, 25.1 ± 1.0, 17.8 ± 3.9 and 18.3 ± 2.6 W m−2 during the summer, winter, monsoon and post-monsoon seasons, respectively at Kadapa. This illustrated that the absorption of solar radiation in the ATM is high which produces a significant amount of heating effect, resulted in a maximum atmospheric heating rate of 0.75 K day−1.

A study on raindrop size distribution variability in before and after landfall precipitations of tropical cyclones observed over southern India

Raindrop size distribution (RSD) characteristics in before landfall (BLF) and after landfall (ALF) of three tropical cyclones (JAL, THANE, and NILAM) induced precipitations are investigated by using a laser-based (PARticleSIze and VELocity - PARSIVEL) disdrometer at two different locations [Kadapa (14.47°N, 78.82°E) and Gadanki (13.5°N, 79.2°E)] in semi-arid region of southern India. In both BLF and ALF precipitations of these three cyclones, convective precipitations have higher mass weighted mean diameter (Dm) and lower normalized intercept parameter (log10Nw) values than stratiform precipitations. The radar reflectivity (Z) and rain rate (R) relations (Z=A*Rb) showed distinct variations in BLF and ALF precipitations of three cyclones. BLF precipitation of JAL cyclone has a higher Dm than ALF precipitation. Whereas, for THANE and NILAM cyclones ALF precipitations have higher Dm than BLF. The Dm values of three cyclones (both in BLF and ALF) are smaller than the Dm values of the other (Atlantic and Pacific) oceanic cyclones. Interaction of different regions (eyewall, inner rainbands, and outer rainbands) of cyclones with the environment and underlying surface led to RSD variations between BLF and ALF precipitations through different microphysical (collision-coalescence, breakup, evaporation, and riming) processes. The immediate significance of the present work is that (i) it contributes to our understanding of cyclone RSD in BLF and ALF precipitations, and (ii) it provides the useful information for quantitative estimation of rainfall from Doppler weather radar observations.

Sodic Soil Reclamation in a Semi-Arid Region Involving Organic Amendments and Vegetative Remediation by Casuarina equsetifolia and Erianthus arundinaceus

In arid and semi-arid regions of the world, certain farming practices and land management have resulted in saline/sodic soils. An experimental study was carried out in a semi-arid region of Southern India, where excess irrigation in the uplands has caused sodic soils in low-lying areas. In order to alleviate the sodicity problem, a combined approach involving application of organic manure, green manuring with Sesbania rostrata and subsequently vegetative remediation by plantation of Casuarina equsetifolia and Erianthus arundinaceus clones was attempted. The use of Erianthus arundinaceus in the integrated treatment along with other amendments is first of its kind in the region and about 20 % of reduction in Exchangeable Sodium Percentage (ESP) was achieved over the initial values. The initial values of ESP in the control plot as wells as treated plot at three different depths varied between 44 and 42.3 %, and after treatment with organic amendments followed by Casuarina and Erianthus plantations, the ESP was reduced to 35–36.5 %. Vegetative remediation in combination with other amendments considerably improved the major and micro nutrients besides nurturing the soil micro-organisms and enzyme activity. At the end of the experiment, about 81 % - 92 % survival rate of the crops was obtained. The cost-benefit ratio analysis based on the market demand for pulpwood ranged between 1:1.75 and 1:2.05. Overall, the experimental results ascertained that the integrated approach for reclamation of sodic soil has been found to be an efficient, cost effective and environmentally sound strategy for semi-arid regions.

Stalagmite δ18O variations in southern India reveal divergent trends of Indian Summer Monsoon and East Asian Summer Monsoon during the last interglacial

Indian monsoon variations for the period around ∼100ka have not been documented from terrestrial archives, while limited data do exist from the Indian Ocean. Some paleoceanographic studies have reported abrupt and stepwise changes in the monsoon intensity during the last deglaciation, but similar observations have not been possible for earlier periods such as the interglacial to glacial transition, mainly because of the coarse resolution (∼500 to 1000 years) provided by marine archives of that age. Here, we report a new δ18O data set from a stalagmite (3-ACN) that grew in the Belum caves, Andhra Pradesh, a semi-arid region in southern India, with a resolution of ∼85 years. Age assignment to different growth layers consistent with associated analytical errors indicates that the record could span ∼9ky during part of Marine Isotope Stage (MIS) 5d-c, from ∼108 to ∼99ka. δ18O variations in this stalagmite, if interpreted using the ‘amount effect’, i.e., 18O depletion of ∼1.5‰ per 100 mm increase in monsoon rainfall, indicate a step-like increase during the transition from the cooler stadial MIS 5d to warmer interstadial MIS 5c, signifying an abrupt reduction in monsoon rain. The new data presented highlight divergent trends between the Indian and the East Asian Summer Monsoons for a time period for which not many high-resolution comparisons are available.

Hydrogeochemical characteristics of Karst Aquifer from a semi-arid region of Southern India and impact of rainfall recharge on groundwater chemistry

The highly heterogeneous and anisotropic property of karst aquifers is a result of the dissolution and karstification of carbonate rocks. Hydrogeochemical evolution and possible water–rock interaction is therefore discussed through spatial and temporal variations in physico–chemical variables of groundwater. Samples were collected both from spring and bore wells. Dissolution of carbonate minerals is the main source of major ions (Ca2+, Mg2+ and HCO3−) in the water. Agricultural activities cause an increase in the concentration of pollution-related ions (nitrates, sulphates, chlorides, etc.). The variability of water chemistry was discussed in terms of different processes like dilution and water–rock interactions, etc. The study reveals a pronounced seasonal hydrochemical variation in the limestone aquifer. In general, the karst groundwater is of Ca–Mg–HCO3 type. Hydrogeochemical signature also helped to analyse the recharge types in the area. The semi-arid climate of the area also contributes to the increase of concentration of certain ions.

In-situ measurements of atmospheric aerosols by using Integrating Nephelometer over a semi-arid station, southern India

Continuous real-time measurements of aerosol scattering properties were investigated at Anantapur (14° 62′ N, 77° 65′ E, 331 m asl), a semi-arid region in southern India for the period of January 2011–December 2011, using a three-wavelength Integrating Nephelometer. Aerosols scattering properties like the scattering coefficient (σsp), backscattering coefficient (σbsp), scattering Ångstrom exponent (Å), backscattering ratio (bλ) and asymmetry parameter (gλ) were measured for the period of study. The average values of (±standard deviation) σsp, σbsp at 550 nm (σsp550, σbsp550) and Å(700/450) were found to be 97 (±9.2) M m−1 and 14 (±0.93) M m−1 and 1.02 (±0.3), respectively. The estimated average values of bλ and gλ at 550 nm from σsp550 and σbsp550 were 0.13 (±0.09) and 0.59 (±0.1), respectively. The maximum asymmetry parameter at 550 nm was found to be 0.63 ± 0.01 in the month of October and minimum (0.52 ± 0.03) during March, which shows the opposite trend with backscattering ratio. Significant correlation coefficients were noticed between different aerosol optical properties. The highest values of σsp550 were observed during weekdays whereas low values during weekends. Scattering Ångstrom exponent for the summer and winter seasons has been consistent with the input of fine mode particles from anthropogenic origin.