Jobin Thomas | Indian Institute of Technology Madras, Chennai (original) (raw)

Papers by Jobin Thomas

Geocarto International, Aug 2, 2022

Lakes and Reservoirs: Research and Management, Dec 1, 2014

Accurate knowledge of sediment quality is essential because it affects the magnitude and trends o... more Accurate knowledge of sediment quality is essential because it affects the magnitude and trends of water quality constituents. There are only a few analyses of sediment quality characteristics using multivariate analysis tools. This study utilizes hierarchical cluster analysis (HCA), factor analysis (FA) and multiple regression analysis (MRA) to demonstrate the usefulness of these techniques to analyse sediment quality for Akkulam–Veli Lake, a tropical coastal lake system in Kerala, India. The variation of sediment quality patterns during the premonsoon (PRM), monsoon (MON) and postmonsoon (POM) periods were assessed with cluster analysis. Factor analysis was used to identify prominent factors influencing sediment quality, while the factors influencing heavy metal partitioning in the sediment and overlying water were identified using multiple regression analysis. The study results indicated the sediment in the upstream portion of the lake was polluted during PRM, with the prominent factors being the ‘heavy metal factor’ and the ‘organic pollution factor’, followed by the ‘phosphorus pollution factor’ and the ‘cadmium pollution factor’. The ‘heavy metal factor’ and the ‘organic pollution factor’ are the prominent factors during MON, whereas the ‘heavy metal factor’, ‘organic pollution factor’ and ‘salinity factor’ were prominent POM factors. The salinity of the overlying water above the sediments plays an important role during PRM and POM, whereas the dissolved oxygen content was important during MON.

Stochastic Environmental Research and Risk Assessment, Feb 2, 2021

The increasing demand for food and clean energy, such as biofuel calls for a sustainable food-ene... more The increasing demand for food and clean energy, such as biofuel calls for a sustainable food-energy nexus in the agriculture sector. Mixed cropping pattern of food and biofuel crops is a viable strategy to meet the escalating demands of the biofuel production at the cost of food production. The implementation of the proposed solutions of simulation–optimization frameworks, at larger spatial scales, is a challenging task. One of the commonly adopted approaches is to implement the solution initially in critical zones that are sensitive to the land management practices and are critical for achieving the objectives. Despite the different techniques to identify the critical zones, this study proposes a new approach to identify the critical zones within a watershed, where the land use changes are essential to improve the social and physical environment while meeting the concurring demands for food and biofuel production. A decision support system (DSS), utilizing the concept of analytical hierarchy process (AHP) is developed to choose the number of optimal solutions from the Pareto-optimal Front to reduce the uncertainty involved in solution adaption by the decision-maker and identification of the critical zone. The results from the study indicate how solution strategies can influence the objective of optimal balance between crop demand and nutrient minimization using different cases. The proposed land use using the developed framework reduced the Total Nitrogen and Total Phosphorous loads by 29% and 38%, respectively from the watershed by converting about 44% of the baseline land use to different cropping patterns with the restriction on minimal food grain and biomass production. The outcome of the framework indicates that the adaptation of more robust objective function for spatial optimization through the developed DSS can reduce the nutrient load in the downstream water.

Total environment research themes, Aug 1, 2023

Ecological Engineering, Feb 1, 2023

Water Environment Research, Jun 1, 2014

The study on bioaccumulation of heavy metals in a lake reveals that during the nonrainy season, a... more The study on bioaccumulation of heavy metals in a lake reveals that during the nonrainy season, accumulation of cadmium in plankton is high in the upstream of the lake where anoxic freshwater condition exists resulting from inflow of urban wastes. Stern action is required to stop the bypass of sewage from the old sewer system especially in the commercial areas of Thiruvananthapuram city, either by augmenting the sewerage system or by treating sewage at the source. During monsoon season, the accumulation of heavy metals-namely lead and nickel, followed by cadmium and chromium-is high in phytoplankton resulting from high nitrate content caused by heavy rainfall. During postmonsoon, lead and nickel accumulation is high. The study emphasizes the need for stormwater management practices for the removal of lead in urban runoff from roads caused by vehicular exhaust, tire wear, and wastes from service stations and workshops.

Sensors

Terrain traversability is critical for developing Go/No-Go maps for ground vehicles, which signif... more Terrain traversability is critical for developing Go/No-Go maps for ground vehicles, which significantly impact a mission’s success. To predict the mobility of terrain, one must understand the soil characteristics. In-situ measurements performed in the field are the current method of collecting this information, which is time-consuming, costly, and can be lethal for military operations. This paper investigates an alternative approach using thermal, multispectral, and hyperspectral remote sensing from an unmanned aerial vehicle (UAV) platform. Remotely sensed data combined with machine learning (linear, ridge, lasso, partial least squares (PLS), support vector machines (SVM), and k nearest neighbors (KNN)) and deep learning (multi-layer perceptron (MLP) and convolutional neural network (CNN)) are used to perform a comparative study to estimate the soil properties, such as the soil moisture and terrain strength, used to generate prediction maps of these terrain characteristics. This s...

Earth Science Informatics

Anthropocene

This study assesses the effect of lockdown, due to the coronavirus disease (COVID-19) pandemic, o... more This study assesses the effect of lockdown, due to the coronavirus disease (COVID-19) pandemic, on the concentration of different air pollutants and overall air quality of a less industrialized region (Kerala) of India. We analysed data from four ambient air quality stations over three years (January to May, 2018-2020) with pairwise comparisons, trend analysis, etc. Results indicated unprecedented reduction in the concentration of the air pollutants: nitrogen dioxide, NO2 (-48%), oxides of nitrogen, NOx (-53% to -90%), carbon monoxide, CO (-24% to -67%) and the particulate matter (-24% to -47% for particulate matter with a diameter of less than 2.5 μm, PM2.5; -17% to -20% for particulate matter with a diameter of less than 10 μm, PM10), as well as the reduction of the National Air Quality Index (NAQI). These reductions indicate an overall improvement of the ambient air quality due to restrictions on transportation, construction, and the industrial sectors during lockdown, even in an area considered less industrial. Despite the general decreasing trend of the concentration of various air pollutants from January to May, suggesting seasonal influences, the trend was intensified in the year 2020 due to the added effect of the lockdown measures. Comparison of results with those from larger and more industrialized cities suggests that the effects of lockdown are more variable, and focused on the levels of gaseous pollutants. Findings from this study demonstrate the far-reaching effects and implications of the COVID-19 lockdown on ambient air quality, even on less industrialized and less urbanized regions.

Environmental Earth Sciences, 2017

The Achankovil Shear Zone (AKSZ) in the Southern Granulite Terrain separates the Trivandrum block... more The Achankovil Shear Zone (AKSZ) in the Southern Granulite Terrain separates the Trivandrum block from the Madurai block. Various geomorphic indices and longitudinal profiles of the river systems in the AKSZ, viz., Achankovil river basin (ARB) and Kallada river basin (KRB), were derived from SRTM DEM to decipher the influence of shearing and deformation on the regional drainage evolution. Although hypsometric analysis of the basins implies old stage of geomorphic evolution, horizontal shifts in the channel plan form are restricted (except in the Tertiary sediments), suggesting the structural controls over the drainage organization, which are also supported by the high topographic sinuosity. The transverse topographic symmetry (T) vectors indicate a southwesterly migration for the upstream channel segments of both ARB and KRB, while the northwesterly migration of the downstream courses can be correlated with the dextral shearing of the AKSZ. Even though the shear zone is considered to be the block boundary between the charnockite of Madurai and khondalite of Trivandrum blocks, the moderate to low profile concavity (h) values are probably the result of suppressing the effect of the blockboundary interactions by shearing and denudation. The study proposes a model for evolution of drainage network in the AKSZ, where the mainstream of the basins was initially developed along NE-SW direction, and later the upstream and midstream segments were reoriented to the NW-SE trend as a result of intense shearing. Overall, the present study emphasizes the significance of geomorphic indices and longitudinal profile analysis to understand the role of shearing and deformation on drainage evolution in transcrustal shear zones.

Ecological Informatics, 2021

Abstract The recurrent forest fires have been a serious management concern in southern Western Gh... more Abstract The recurrent forest fires have been a serious management concern in southern Western Ghats, India. This study investigates the applicability of various geospatial data, machine learning techniques (MLTs) and spatial statistical tools to demarcate the forest fire susceptible regions of the forested landscape of the Wayanad district in the southern Western Ghats (Kerala, India). The inventory map of 279 forest fire locations (period = 2001–2018) was developed via Sentinel 2A satellite images, NASA fire archives, and field visits. The forest fire susceptibility modelling involves twelve influencing factors, such as ambient air temperature, wind speed, rainfall, relative humidity, atmospheric water vapor pressure (WVP), elevation, slope angle, topographical wetness index (TWI), slope aspect, land use/land cover (LU/LC), distance from the road and distance from the villages. Considering the varying level of performances (i.e., receiver operating characteristics-area under curve (ROC-AUC) values ranging from 0.869 to 0.924 in the testing phase) of the MLTs, viz., artificial neural network (ANN), generalized linear model (GLM), multivariate adaptive regression splines (MARS), Naive Bayesian classifier (NBC), K-nearest neighbour (KNN), support vector machine (SVM), random forest (RF), gradient boosting machine (GBM), adaptive boosting (AdaBoost) and maximum entropy (MaxEnt), we propose a weighted approach to characterize the forest fire susceptibility of the region using the outputs of the different MLTs. The proposed method demonstrates improvement in accuracy (AUC = 89%) for mapping the forest fire susceptibility of the region compared to the individual MLTs (AUC = 71.5 to 86.9%) while validating with the recent forest fire data (i.e., 2019–2021). This study suggests that roughly one-third of the study area is highly susceptible to the occurrence of forest fires, implying the severity of the disturbance regime. The analysis also indicates the role of anthropogenic factors in the occurrence of forest fires in the region. It is expected that the demarcation and prioritization of the forest fire susceptibility zones in the region, which is a part of one of the global biodiversity hotspots, have significant implications on biodiversity conservation at a regional scale.

Groundwater for Sustainable Development, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Earth Systems and Environment, 2019

The increasing demands for the groundwater resources along with decreasing availability, especial... more The increasing demands for the groundwater resources along with decreasing availability, especially in the hard-rock aquifers, call for sustainable groundwater management in India. The present study attempts to identify the potential zones for groundwater recharge, through water conservation measures, in a tropical river basin of Kerala (India), viz., Ithikkara River Basin. The approach enables us to locate the areas suitable for different groundwater recharge structures using remote sensing, geospatial data, and multi-influencing factor technique in the GIS environment. The geo-environmental variables used in the study are lithology, geomorphology, available space for recharge, slope angle, lineament density, soil texture, rainfall, percentage of sand fraction in soil, land use/land cover, and drainage density. The results indicate that lithology, available space for recharge and geomorphology, is the significant variables controlling the groundwater recharge of the study area. The estimated recharge potential zones of the basin are classified into four different classes based on their suitability for groundwater recharge, viz., very good, good, moderate, and least recharge potential zones. Roughly, 50% of the basin area belongs to very good and good recharge zones and is suitable for implementing various groundwater-recharging mechanisms. Based on the variability in the geo-environmental factors of the study area, different artificial groundwater recharge structures (i.e., rainwater infiltration pits, percolation ponds/trenches, injection wells/pond-cum-injection wells and check dams) are suggested using a rule-based approach. The results of the study will be beneficial to the formulation of sustainable groundwater management plans for the region.

Remote Sensing Applications: Society and Environment, 2019

Journal of the Indian Society of Remote Sensing, 2018

Basin-wise DEM-based Automated Morphometry (BaDAM) toolbox, an automated solution for drainage ba... more Basin-wise DEM-based Automated Morphometry (BaDAM) toolbox, an automated solution for drainage basin morphometric analysis, is presented in this paper. The toolbox, being scripted in Python, can be easily integrated with ArcGIS 10.0 version, and customizations can be implemented effortlessly. The BaDAM toolbox has been tested for computation of morphometric attributes of a tropical river basin in Kerala (India) using SRTM DEM (30 m), and the analysis was carried out successfully with less time complexity and with significant efficiency. Further, the results of the DEM-based morphometric analysis generated by the toolbox showed good agreement with the results of a previous study using SRTM data for the same river basin. It is suggested that the toolbox, which takes care of most of the inherent limitations of the existing programs/tools, can be used for DEM-based basin morphometric analysis for generating comparatively quicker and accurate results.

International Soil and Water Conservation Research, 2018

Soil erosion and deposition in a tropical mountainous river basin, viz., Pambar River Basin (PRB)... more Soil erosion and deposition in a tropical mountainous river basin, viz., Pambar River Basin (PRB), in a rain shadow region of the southern Western Ghats (India) were modelled using Revised Universal Soil Loss Equation (RUSLE) and transport limited sediment delivery (TLSD) function in GIS. Mean gross soil erosion in the basin is 11.70 t ha-1 yr-1 , and is comparable with the results of previous soil erosion studies from the region. However, mean net soil erosion from the basin is 2.92 t ha-1 yr-1 only, which is roughly 25% of the gross soil erosion. Although natural vegetation belts show relatively higher gross-and net-soil erosion rates (mainly due to high LS and C factors), their sediment transport efficiency is remarkably less, compared to the land use/ land cover types with anthropogenic signatures (i.e., plantations and croplands). Despite the lesser amount of annual rainfall, the high rates of soil loss from the semi-arid areas of the basin might be the result of the poor protective vegetation cover as well as isolated high intensity rainfall events. The study highlights the significance of climate-specific plans for soil erosion management and conservation of the soil resources of the basins developed in rain shadow regions.

Hydrological Sciences Journal, 2018

The long-term average annual soil loss (A) and sediment yield (SY) in a tropical monsoon-dominate... more The long-term average annual soil loss (A) and sediment yield (SY) in a tropical monsoon-dominated river basin in the southern Western Ghats, India (Muthirapuzha River Basin, MRB; area: 271.75 km 2) were predicted by coupling the Revised Universal Soil Loss Equation (RUSLE) and sediment delivery ratio (SDR) models. Moreover, the study also delineated soil erosion risk zones based on the soil erosion potential index (SEPI) using the analytic hierarchy process (AHP) technique. Mean A of the basin is 14.36 t ha-1 year-1 , while mean SY is only 3.65 t ha-1 year-1. Although the land-use/land cover types with human interference show relatively lower A, compared to natural vegetation, their higher SDR values reflect the significance of anthropogenic activities in accelerated soil erosion. The soil erosion risk in the MRB is strongly controlled by slope, land use/land cover and relative relief, compared to geomorphology, drainage density, stream frequency and lineament frequency.