2. Thesis and Dissertations
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Item Tidal Energy Potential Estimation and Impacts on Hydrodynamics around Tidal Power Systems along the Indian Coast(National Institute of Technology Karnataka, Surathkal, 2021) Mendi, Vikas; Rao, Subba; Seelam, Jaya KumarTidal energy is the energy derived using the tides. Most of the tidal energy feasibility studies are conducted for barrage method of tidal energy extraction. In Indian scenario, the observed conditions and the methods proposed are mostly for the barrage method mainly in the states of Gujarat in the west and West Bengal in the east where the tidal range is maximum. Assessment of energy extraction from barrage method has not been carried out in the southern parts of India due to low to medium tidal range. The first objective mainly focuses on tidal energy resource availability and the energy that can be harnessed from tides along the coast of India. Two methods are considered viz. tidal barrage and tidal stream energy. Out of 471 tidal inlets identified in 9 maritime states along the Indian coast, 130 inlets are shortlisted considering a threshold of 2.53 Mm3 tidal prism and potential energy was estimated. Total potential energy estimate considering 130 inlets is 2254.906 MW. Further 107 inlets are shortlisted considering both tidal prism greater than 2.53Mm3 and inlet throat width greater than 63m and the corresponding potential energy is estimated as 2127.281 MW. The Kinetic energy estimated was 11.68kW, 5.60kW and 25.64kW at Chapora, Mandovi and Zuari respectively. The second objective intends to study the impact of tidal energy of local hydrodynamics.The turbines are placed at the locations where highest tidal currents were observed as presented in objective 1. Five cases were considered where the simulations were carried for different locations of the tidal turbine. Total energy generated by 0.5m diameter turbine was estimated to be 118kW. Whereas the 1m diameter turbine increased the energy to 409.35kN. The total energy estimates for the turbines in parallel and turbines in tandem considering 0.4 m/s threshold for current speeds was approximated to 417.5kW and 409.35kW respectively. The morphodynamics were simulated and the sea bed morphology of Zuari creek was studied. The results of the coupled model proved that the location chosen for tidal energy extraction does not exhibit sediment transport and longer durations of simulations are required. In the third objective, tidal lagoons are established and the morphodynamics due the energy extraction are studied. A tidal lagoon can be constructed either on an existing natural rock/headland or completely by artificial means. It can either be constructed nearshore adjacent to the coast of in the tidal reservoir where conditions are feasible. Locations for the construction of tidal lagoons are identified along in Maharashtra (Jaigad 1 and Jaigad 2). The potential energy that can be extracted from the established tidal pools is estimated to be 3.69MW and 1.3MW respectively. Results of morphodynamic study for 20 days are analyzed. The bed level changes observed at Jaigad 1 and Jaigad 2 prove less sensitive to hydrodynamics. Bed level changes observed are of the order 0.04m (in 20 days) due to the construction of tidal barrage.Item Experimental Studies on Friction Coefficient of Al 6061-T6 Alloy Contacts under Full Sliding(National Institute of Technology Karnataka, Surathkal, 2021) I, Srinivasula Reddy.; Kaliveeran, VadivuchezhianAim of the present research work is to study dry sliding coefficient of friction of aluminium to aluminium contacts in detail and to study evolution of coefficient of friction with change in normal load, sliding speed and temperature. Dry sliding experiments were conducted using pin on disk type tribometer. Specimens (both pin and disk) were fabricated using Al 6061-T6 alloy. The disk specimen has dimensions of 165 mm diameter and 8 mm thickness; the pin specimen dimensions are 30 mm length, 6 mm x 6 mm cross-section and 3 mm radius of curvature at cylindrical contact. Experiments were conducted with cylinder on flat contact configuration. Dry sliding experiments were conducted by applying normal loads of 1 kg, 1.5 kg and 2 kg; at different sliding speeds of 1.25 m/s, 2 m/s and 3 m/s; at different temperatures room temperature (31 ± 1 °C), 60 °C, 100 °C and 150 °C. The coefficient of friction at contact interface is influenced by both frictional heat generated and external temperature. The frictional heat at contact interface was estimated by measuring temperatures at 3 mm and 7 mm from contact interface of pin specimen during dry sliding experiments. One-dimensional inverse heat transfer model was developed using Finite Element Method and Beck’s algorithm to estimate the contact interface temperature. The inverse heat transfer model was validated by using ANSYS transient thermal analysis. Maximum bulk temperature at contact interface was observed for all the experimental conditions at room temperature. Temperature due to frictional heat at contact interface increased with increase in normal load and sliding speed. The maximum frictional heat of 100 °C was observed at 2 kg normal load and 3 m/s sliding speed condition. The frictional heat and external heat source temperatures are the reasons for formation of oxide layer at contact interface during sliding which ultimately changes the coefficient of friction of contact pair. Coefficient of fiction, after the first cycle of sliding, stabilized stage, unsteady state and steady state are reported elaborately in this study. The coefficient of friction and wear rate were more influenced by increase in normal load than by increase in sliding speed and temperature. Adhesive and abrasive wear mechanisms were observed in dry sliding of Al 6061-T6 alloy contacts from the microscopic analysis of worn contact surfaces. Under normal loads of 1 kg and 1.5 kg, Al 6061-T6 alloy showed better wear resistance at higher temperatures when compared to that at room temperatureItem Satellite Based Top-Down Approach for Modelling Aerosol Source Strength and its Application in Discerning Rainfall Trends(National Institute of Technology Karnataka, Surathkal, 2021) Nizar, Sinan.; Dodamani, B. M.This thesis is dedicated to study the possible relationship between the distribution of aerosols and rainfall patterns. The thesis proposes a new approach, wherein aerosol sources are investigated rather than the aerosol loading in a region to understand its variation with rainfall. The study first investigates the influence of meteorological parameters indicating both advection and diffusion on the spatiotemporal distribution of aerosols over the Indian subcontinent and the adjacent Indian Ocean. The research inferences are then used to develop a model to estimate aerosol emissions using satellite data. Further, the spatial aerosol source distribution is used to investigate rainfall variability over southern India. The prevailing meteorological conditions that influence the advection and diffusion of the atmosphere govern the distribution of atmospheric particles from its sources. The present study first explores the spatiotemporal distribution of atmospheric aerosols over the Indian subcontinent and its dependence on the prevailing meteorological conditions. Eleven years of Aerosol Optical Depth obtained from the Moderate Resolution Imaging Spectroradiometer along with meteorological parameters extracted from reanalysis data are analysed at monthly timescales. Wind speed, wind divergence and planetary boundary layer height are studied as parameters for advection and diffusion of atmospheric aerosols. The result shows the importance of both advection and diffusion in distributing aerosols over the region. The result shows higher aerosol loading during the monsoon season with increased spatial variability.Wind speed and divergence correlate with AOD values both over land (R = 0.75) and ocean (R = 0.82) with increased aerosol loading at higher wind speeds, which are converging in nature. Owing to the varied climatology of the Indian subcontinent, land and ocean areas were classified into subregions. Analysis was carried out over these subregions to infer the influence of meteorological conditions on aerosol loading. Results are indicative of a distinct characteristic in the prevailing meteorological conditions that influence the distribution of ii certain aerosol types. Further, the PBLH was analysed as an indicator of atmospheric diffusion to infer its importance in aerosol distribution. The results indicate that PBLH explains almost 30 to 90% of the total variance in AOD over the subregions which is particularly evident during the winter and pre-monsoon seasons. The study further uses a Lagrangian approach to the Advection Diffusion Equation to estimate the transported aerosols and hence the Aerosol Source Strength using satellite-measured Aerosol Optical Depth (AOD) and reanalysis wind data. This top-down approach is based on the advection and diffusion of atmospheric aerosols considering wind circulation and atmospheric conditions rather than using indicative parameters. To validate the current top down approach, the study first utilises the AOD measurements from the GOES-16 for California and then applies the methodology over southern India using MODIS to identify aerosol hotspots. The results over California are indicative of higher ASS around wildfire locations. The ASS values also show good correlation (R2 = 0.886) with Fire Radiative Power (FRP) obtained from TerraMODIS fire product. Themethodwas further applied to investigate the spatial correlation of ASS with power plant density, which reveals a steady increase in ASS with power plant density (R2 = 0.82). Finally the study investigates the possible relationship between rainfall and aerosol source distribution over southern India during the pre-monsoon season. Aerosol and rainfall trends are computed using Mann Kendall trend test and are correlated spatially with AOD and ASS. To further understand the relationship, cloud microphysics is also investigated. The results indicate that, though the aerosol loading initially supports cloud formation resulting in deeper and wider clouds, higher aerosol loading inhibits cloud formation resulting in narrow and shallow clouds. This in turn decreases rainfall at higher aerosol loading with smaller cloud radius.Item Numerical Model Studies to Predict the Wind-Wave Climate Considering Climate Change Effects(National Institute of Technology Karnataka, Surathkal, 2021) K, Sandesh Upadhyaya.; Rao, Subba; ManuThe waves propagating over an area under the action of the wind is termed as wind waves. The disturbances on the ocean surface by the wind are restored to a calm equilibrium position by the action of gravity. The fundamental element in the wind-wave generation is the interaction between air and ocean. During this interaction, there is an energy and momentum transfer between the atmosphere and ocean. The climate change affects the atmospheric temperature which in turn alters the wind patterns. The wave conditions change according to the wind pattern. Studies on global climate changes and extreme weather events have fascinated researches all over the world. Climate change, a global phenomenon, is a consequence of ever-increasing greenhouse gas concentration and is considered a serious threat to mankind. Climate change is a phenomenon triggered by natural and anthropogenic activities, which is one of the most discussed topics in the research community today. An increase in global sea level, changes in wind pattern and an increase in the frequency of extreme wave events which is caused by climate change have critical impacts on the coastal population around the world. Indian coast measures about 7500 km along with the nine coastal states which host marine and coastal biodiversity. Thirteen major ports and associated activities play a prominent role in coastal population concentration of about 14% along the Indian coast. The coastal and offshore structures are typically designed for the significant wave height (HS) corresponding to a specific return period and it is, therefore, necessary to know possible changes in their magnitudes at different locations of interest. Structures built in the sea are traditionally designed according to historical climate observations or hindcasted data. For structural safety, consideration of such climate change effects is highly desirable. Computational advancements in recent times have resulted in various General Circulation Models being developed and effectively used for assessing the atmospheric and ocean circulation. The performance of these modelled result can be compared with the in-situ measurements of shorter duration. Forecast of the climate parameters incorporating climate change effects are developed. These data products can be used to develop numerical wave models for long term analysis of wind and wave patterns which will aid in the design of coastal and offshore structures. i i In the present study, hindcasting from 1980 for the Indian domain is performed from reanalysed gridded global wind speed dataset called ERA-Interim. The performance of this global dataset is assessed by comparing it with in-situ measurements recorded at the east and west coast of India. As the ERA-Interim dataset showed a good match with the in-situ records these long-term wind speeds are used as an input to the numerical wave model. MIKE 21 SW numerical wave model is developed for the Indian domain with coordinates - 4º to 30º N 40º to 95ºE. Significant wave heights from this wave model driven by ERA-Interim wind speeds are extracted at locations nearshore to Karwar and offshore OB03 location for validation. After validation, the numerical model is used to perform longterm wave analysis, shoreline analysis, assessment of wind-wave climate along the Indian coast and wave climate predictions along Karnataka coast for the near future. The numerical model output depends on the input which is global wind speed dataset. Wind speed analysis is initially performed before using it in the numerical model. As ERA-Interim dataset does not provide forecasts, global wind speeds provided by the CMIP5 database is considered in this study. Wind speed projections from 38 different CMIP5 global models are compared against ERA-Interim global wind speeds for the Indian domain. The performance of datasets is graphically evaluated based on Taylor plots. Initially, statistical analysis of monthly wind speeds from 1980 to 2005 is performed to arrive at four best performing datasets for the Indian domain. Further, a nowcast study on daily wind speeds from 2006 to 2018 considering the four climate change scenarios termed as Representative Concentration Pathways (RCPs) is carried out. From the nowcast analysis, an Italian CMIP5 dataset called CMCC-CM for RCP 4.5 matched well with the real-time reanalysed wind speeds provided by ERA-Interim. Hence in the present study, wave climate predictions for the Indian domain is based on wind speeds driven by CMCC-CM RCP 4.5. The long-term analysis is performed based on the five probability distributions such as Log-normal distribution, Gumbel distribution, Fretchet distribution, Exponential distribution, and Weibull distributions to arrive at significant wave height with 10 and 50 year return period for New Mangaluru port location. Initially, long-term analysis is performed on in-situ records measured for 5 years near New Mangaluru Port. From this analysis, Weibull distribution with α=1.3 showed good performance and is used to arrive at significant wave heights with 10 and 50 year return period. The same approach is extended on the MIKE 21 simulated significant wave heights from 38-year ERA-Interim hindcast. The results showed 2.6% and 5.44% increase in significant wave height with 10 year and 50 year return period at the location studied. ii i A shoreline analysis is performed using LITPACK tool along the coast adjacent to the New Mangaluru Port. The volume of sediment transport is analysed and the shoreline changes from 1980 to 2015 is studied to understand the erosion and accretion patterns. The performance of the numerical model matched well with the satellite measurements. In an attempt to explore the renewable energy potential along the Indian coast the numerical wave model is also used to assess the wind-wave climate based on ERA-Interim wind speed data of 38 years. The results showed amongst the locations studied off Goa, Karnataka, Kerala, Tamil Nadu, and Andhra Pradesh had good potential to extract offshore wind energy from offshore wind turbines. MIKE numerical model driven by wind speeds from CMCC-CM RCP 4.5 up to the year 2070 is used to simulate the wave climate along the Karnataka coast. The monsoon wave climate is studied to arrive at wave parameters with 10 and 50 year return period at six locations along the Karnataka coast.Item Integrated Water Resource Modelling for Improved Agricultural Productivity in OMO-Gibe Basin Ethiopia(National Institute of Technology Karnataka, Surathkal, 2021) Kebede, Mudesir Nesru.; Shetty, Amba.; Nagaraj, M. K.The lack of data in many river basins hinders the effective management of water resources. This is true in many river basins of Ethiopia. In this study, remote sensing images and the hydrological model were used jointly to bridge the gap in understanding of the hydrological processes of a watershed with sparse measured data. Understanding of water balance components is imperative for proper policy and decision-making. Such assessments are not available in many river basin across the globe, specifically in the upper part of the Omo- Gibe basin (UOGB) Ethiopia. The objective of this study was; (i) to explore the possibility of assessing consumption and availability of water using freely available satellite data and secondary data, (ii) to test the efficiency of satellite-based actual evapotranspiration in the HBV hydrological model to render the catchment water balance using multi-variable calibration and (iii) to come up with a strategy to increase cereals production by 2030 using available water resources in the upper Omo-Gibe basin. The Surface Energy Balance System (SEBS) is used to estimate spatiotemporal variability of actual evapotranspiration of the basin, while the Hydrologiska Byran's Vettenbalansavdeling (HBV) rainfall-runoff hydrological model is used to simulate streamflow as well as actual evapotranspiration. A spatial average of rainfall was computed using the Thiessen polygon approach. Actual evapotranspiration (ETa) was estimated through the Surface Energy Balance System (SEBS). Temporal MODIS images were used to estimate the spatial distribution of actual evapotranspiration covering the crop cycle during the study year. Additionally, Priestly and Taylor's approach was used to estimate reference evapotranspiration (ET0). The result of estimated precipitation and ETa showed that the UOGB received 41,080Mm3 of precipitation for the given study period, while 24,135Mm3 become evapotranspired. The assessed outflow from the basin is 17.6% of the precipitation and demonstrated that water is a scarce resource in the UOGB. Conventional practice of calibration of any hydrological model in any river basin is performed using a single hydrological variable, namely streamflow. Spatially distributed hydrological modelling provides an opportunity to enhance the use of multi-variable iii calibration models. Five years (2000-2004), meteorological data, streamflow, and actual evapotranspiration (ETa) based on remote sensing were used for calibration and validation purposes. The performance of the HBV model and the efficiency of SEBS-ETa were evaluated using certain calibration criteria (objective function). The model is first calibrated using only streamflow data to test HBV model performance and then calibrated using a multi-variable (streamflow and ETa) dataset to evaluate the efficiency of SEBSETa. Both model setups were validated in a multi-variable evaluation using streamflow and ETa data. In the first case, the model performed well enough for streamflow and poor for ETa, while in the latter case, the performance efficiency of SEBS-ETa and streamflow data shows satisfactory to good. This implies that the performance of hydrological models is enhanced by employing multi-variable calibration. Maize crops production yield in the water-scarce UOGB, can be increased by increasing crop water productivity and improving agricultural management. Based on the CWP and ETa/ETp analysis, the seasonal average Abelti maize CWP is 0.3 Kg/m3. In addition, the ETa of rainfed maize over the main maize growth period is 520 mm per season. Crop production function analysis and its planting can be studied as a function of the amount of seeds, fertilizers, and water utilized to evaluate the crop yield in the study area for the rainfed maize area. A total of 30,287.17 ha of suitable pastoral land has been converted/expanded to a rainfed maize area in the three slope classes (namely fairly, suitable land sloping classes, the moderately suitable land sloping classes, and the average suitable sloping class)of the basin. The two strategies identified to meet the expected 2030 UOGB rainfed maize production target are assessed based on a one-fourth, two-fourth, and three-fourth increase in yield gaps. In the first strategy, the increase in yield gaps by onefourth, two-fourth, and three-fourth contributes 23.12%, 46.23 %, and 69.35% of the total targeted production in the current rainfed maize area of the basin in the same order. Whereas, in the second strategy, the increase in production for additional suitable land contributed 0.80, 0.39 and 0.68, 1.61, 0.79 and 1.36, and 2.41, 1.18, and 2.04% of the planned target production in the same order.Item Simulation of the Hydrological Impacts of Climate and Land Use/Cover Change on Tikur Wuha Watershed in Ethiopia(National Institute of Technology Karnataka, Surathkal, 2021) Demmsie, Abiot Ketema.; Dwarakish, G. S.The study was carried out on the Tikur Wuha watershed (TWW) in Ethiopia with four specific objectives: simulation of the potential impact of climate change on hydro-meteorological variables, evaluation of the hydrological impacts of land use/cover (LU/LC) change, examination of the trend and variability of hydro-meteorological variables, and prioritisation of the sub-watersheds for soil and water conservation (SWC) measures based on soil loss rate (SLR). The LU/LC map was developed using a supervised classification method. The impact of LU/LC and climate change on streamflow was assessed using the Soil and Water Assessment Tools (SWAT) hydrological model. The Mann-Kendall trend test and Sen's slope estimator were employed for the trend and size of the trend, respectively. A Universal Soil Loss Equation (USLE) was used to estimate the SLR. The result revealed that the Bega, Kiremt, and annual rainfall increased for all scenarios. In contrast, the Belg rainfall decreased in all cases except for RCP8.5 at the end of the century. Both the minimum and maximum temperatures increased for all scenarios. The annual average streamflow in TWW increased in all cases except a slight reduction in the RCP4.5 scenario in mid-century. Climate change affects the streamflow in the study watershed by increasing the wet season flow and reducing the dry season flow. The LU/LC detection shows a steady expansion of cropland and built-up areas and the withdrawal of shrubland, swampy, water bodies, and grassland during the 1978 to 2017 periods. The LU/LC changes increased the average annual streamflow by 14.77% from 1978 to 2017. The LU/LC change had a dominant role in the hydrological responses of the TWW. The trend analysis discovered that the average annual rainfall exhibited an insignificant declining trend of 20.8 mm/decade at a watershed scale. The temperature showed a statistically significant rising trend, with the minimum temperature rising faster than the maximum temperature. The Tikur Wuha River's streamflow increased at 21.16 MCM/decade from 1980 to 2002. The average SLR of the watershed is 14.13 t ha-1yr-1. It is larger than the maximum soil loss tolerance of the watershed and higher than the country's average SLR. The SWC measures should be implemented rapidly in the TWW, consistent with the priority watersheds' rank.Item Gravity Wave Damping by Stratified Porous Structures(National Institute of Technology Karnataka, Surathkal, 2020) Venkateswarlu; Karmakar, Debabrata.In the present study, wave transformation due to multiple porous structures in the presence and absence of vertical rigid wall, barrier-rock breakwaters of various configurations, multiple horizontally stratified porous absorbers, vertically stratified porous structure lying on flat seabed, elevated seabed and stepped seabed is analysed under the oblique wave incidence. The eigenfunction expansion method using the continuity of pressure and velocity along with mode-coupling relation is adopted based on linearized wave theory. The direct analytical relations are derived for finding the wave reflection and transmission coefficients due to porous breakwaters of various structural configurations. In the preliminary stage, the analytical results are validated with numerical and physical model results available in the literature. As a special case, a comparative study is performed between the vertical rigid wall, permeable wall and stepped wall away from the double horizontally stratified wave absorbers. The vertical and stepped wall shows almost similar values of wave reflection at each of the resonating crests, but minimal values of the resonating trough in wave reflection is obtained from the stepped wall. A comparative study is performed between single and multiple porous structures of fixed structural width and depth. The 42% reduction in wave transmission is achieved with double porous structures as compared with single porous structure for uniform structural width, which may be due to wave damping in the free spacing available between the two structures. The distribution of incident wave energy in the form of wave reflection and transmission is effective in the case of horizontally stratified porous structure as compared with other structures. The vertically stratified porous structures performance is partially dependent upon structural width. Higher structural width effectively reduces the wave transmission as compared with conventional porous structures. The effect of each layer porosity, friction factor, structural width, incident wavelength, number of structures, angle of incidence, free spacing and trapping chamber effect on wave reflection, transmission damping, fluid force on seaward/leeward sides of breakwater and force on vertical wall is analysed for various types of porous structures. The critical angle due to standing waves, fluid resonance in the free spacing and clapotis has an efficient role in the design of porous structures.Item Hydroelastic Analysis of Floating and Submerged Flexible Structures(National Institute of Technology Karnataka, Surathkal, 2020) M, Praveen K.; Karmakar, Debabrata.The present work mainly deals with a class of physical problems in the broad area of wave structure interaction related to hydroelasticity. In the present study, the major emphasis is given • to analyse the hydroelastic behaviour of the very large floating structure based on the Timoshenko-Mindlin’s plate theory in both finite and shallow water depth, • to illustrate the significance of periodic array of articulation, change in bottom topography and wave attenuation due to the presence of vertical barriers in the hydroelastic analysis of floating structures which are of recent scientific interest in the field of Ocean and Coastal Engineering. In the present study, the generalized expansion formulae along with the orthogonal modecoupling relation is utilized to analyse the wave interaction with very large floating structure. The study is performed to analyse the influence of different edge support conditions on the hydroelastic behaviour of the floating elastic plate and the numerical results obtained based Timoshenko-Mindlin plate theory is compared with the EulerBernoulli plate theory. The gravity wave scattering by single and multiple articulated floating finite elastic plates are analyzed based on small amplitude linearized water wave theory. In the case of periodic array of multiple articulated floating elastic plates, the solution for the boundary value problem is analyzed by using both eigenfunction expansion method and wide-spacing approximation method. The transformation of gravity wave due to multiple variations in bottom topography in the presence of articulated floating elastic plate is studied by using orthogonal mode-coupling relation. Further, using shallow water approximation, the flexural gravity wave scattering due to (i) articulated floating elastic plates and (ii) abrupt changes in bottom topography are analyzed and the explicit relation for the wave scattering coefficients are obtained. Finally, surface gravity wave scattering due to the presence of vertical barriers along with the floating articulated elastic plate are analysed and the energy relation associated with transformations of gravity waves in the presence of vertical porous barrier is discussed. The numerical results for the reflection and transmission coefficients, plate deflection, strain along the floating elastic plate, bending moment and shear force are computed in different cases and analyzed.Item Soil Moisture Variability and Hydrological Impact Assessment of Land Cover Change(National Institute of Technology Karnataka, Surathkal, 2020) M, Diwan Mohaideen M.; Varija, K.Water availability in a region depends on how precipitation over the region is transformed into various forms after reaching ground such as evaporation losses, runoff, infiltration, soil moisture, and ground water storage etc. Land Use / Land Cover (LU/LC) changes adversely affect the aforementioned components. Particularly, the effects of LU/LC changes on catchment hydrological responses, especially vegetative cover (forest, scrubs and cropland), affect the evapotranspiration. Further, rapid urbanization due to LU/LC changes leads to extent of impervious surface and thereby, impacts the infiltration rates as well as recharge. The LU/LC change impact on the hydrologic system is region specific, and each region is characterized by its own hydrology, terrain, climate and also anthropogenic factors. Therefore, a detailed assessment of LU/LC change impacts on hydrology is required, specifically at the region with seasonally limited water availability. It is emphasized by many researchers that the physically-based, distributed hydrological models along with remote sensing capabilities are more suitable for assessing the LU/LC change impacts on the hydrologic system. Further, Soil moisture, being a critical state variable, its knowledge is of paramount importance in several hydrological applications (e.g., runoff modeling and flood forecasting, agricultural monitoring and drought monitoring). The magnitude of soil moisture variability often under estimated and the spatial pattern of soil moisture is not consistent, and it is largely varying across the site and climate with the influence of heterogeneity in LU/LC, topography, soil properties, precipitation and evapotranspiration. Hence, the characterization of soil moisture variability is essential. The work reported in this thesis aims at understanding the soil moisture variability and land cover change impacts in an agricultural dominant semi-arid basin. The Variable Infiltration Capacity (VIC) model, a physically based, semi distributed hydrological model was used to simulate the hydrologic responses of the basin for different LU/LC scenarios (the year 2000 and 2010) with multiple soil layersiv parameterization (three soil layers: 0 – 10 cm, 10 – 45 cm and 45 – 100 cm). The total drainage area of the basin was discretized into number of model grids (5.5 km resolution: totally 1694 grids), and the input parameterization of the model was made at each grid level. The major input parameters to the model are meteorological forcing (Precipitation, Tmax, Tmin), soil characteristics, land surface vegetation classes (vegetation parameter & library) and topography. This study demonstrated a methodological frame work for improved vegetation parameterization to the model simulation. Moderate Resolution Imaging Spectroradiometer (MODIS)-derived 8-day Lear Area Inded (LAI) time-series data was used to sub-group agricultural dominant areas into major crop groups and corresponding monthly vegetation phenology in terms of LAI, albedo, height, root distribution were arrived. This exercise enabled improved definition of vegetation parameterization for the study area, incorporating the region specific conditions. Firstly, the model was calibrated and validated using the observed stream flow data collected at two different locations for the period 1994 – 2001. The model parameter values were adopted for each model grid (about 5.5 km) based on the saturated hydraulic conductivity at that grid by trial and error method. To assess the hydrological impacts of LU/LC change on the flow regime of the basin, the model was run using the two LU/LC conditions separately with the same observed meteorological forcing and soil data. The changes attributed to LU/LC at basin level indicate that the surface runoff and baseflow decreased by 18.86 and 5.83% respectively. The evapotranspiration increased by 7.8%, mainly because of the agricultural crops. The variability in hydrological components and the spatial variation of each component attributed to LU/LC was further assessed at the basin grid level. The majority of the basin grids showed an increase in evapotranspiration (80 % of basin grids) and subsequent decrease in runoff and baseflow (79 and 85% of basin grids, respectively) with resepect to LU/LC change. Further, the spatio-temporal variation of soil moisture was assessed using the model simulated soil moisture along with three different satellite derived surface soil moisture products (SM-CCI, SM-TRMM and SM-AMSRE). It was found from the analysis that the impacts of LU/LC changes on soil moisture were more evident in the deeper layers (45 cm and 100 cm). The soil moisture decreased byv an average of 14.43 and 18.21% (percentage change), particularly in dry periods at second and third layers, respectively. Further, the modeled soil moisture along with three different satellite surface soil moisture products were investigated for its spatio-temporal variability in the basin. The soil moisture in the top layer (up to 10 cm) showed high temporal variations. However, the mean soil moisture was found almost constant during the summer and winter seasons. The basin showed high variability in soil moisture during the intermediate wetness condition. Further, the spatial variability of the soil moisture during the wetting period (June-August) was high compared to drying period (December – February). Based on the analysis performed in this study, 29 (out of total model grids - 1694) representative grid locations were identified in the basin. These locations could be effectively considered for installing observational network mainly for monitoring soil moisture in near real-time.Item Modeling Evapotranspiration using Remotely Sensed Spatial Contextual Information(National Institute of Technology Karnataka, Surathkal, 2020) C, Sanjay Shekar N.; Nandagiri, Lakshman.Characterization of the spatial and temporal variabilities of Actual Evapotranspiration (AET) or Latent Heat Flux (λET) from heterogeneous landscapes is essential in studies related to hydrology, climate, agriculture, irrigation, water resources engineering and management and environmental impact assessments. AET/λET is influenced by a large number of factors related to climate, vegetation and soil moisture and therefore its direct measurement is rendered difficult especially over large spatial domains. The only feasible and convenient way to map AET over regional or catchment-scales is through the use of remote sensing technology and accordingly, numerous world-wide studies have focussed on this approach. Among these, the Penman-Monteith (PM) and Priestley-Taylor (PT) methods have proved to be most popular on account being simple but yet providing reasonably accurate estimates of regional AET. However, most previous studies have implemented satellite-based PM and PT AET estimation approaches to crop lands located in arid to semi-arid regions. Therefore, the main focus of the present study is to develop satellite-based AET estimation methods which can be applied to wet tropical regions possessing natural vegetation. The current research work is aimed at the development, application and evaluation of methodologies for estimation of AET/λET by the PM approach using Moderate Resolution Imaging Spectrometer (MODIS) satellite imagery. The feasibility of extracting the bulk surface conductance (Gs); an important parameter in the PM model, from the spatial contextual information present in a scatter plot of Land Surface Temperature (LST) versus Fraction of Vegetation (Fr) is explored in this study. Also, few studies seemed to have compared the performances of the PM and the PT model and other similar models using the same dataset and therefore this exercise was taken up. Using a general expression for Gs derived by assuming a two-source total λET (canopy transpiration plus soil evaporation) approach proposed by previous researchers, minimum and maximum values of Gs for a given region can be inferred from a trapezoidal scatter plot of pixel-wise values of LST and corresponding Fr. Using these as limiting values, Gs values for each pixel can be derived through interpolation and subsequently used with the PM model to estimate λET for each pixel. The proposed methodology was implemented in 5 km x 5 km areas surrounding each of four AsiaFlux tower sites located in different countries of tropical south-east Asia which were selected based on certain specific criteria. MODIS data products of MOD11A1 product of Land Surface Temperature (LST) at 1000 m resolution, MOD09GA product of Land Surface Reflectance (LSR) at 1000 m resolution, MOD15A2 product of Leaf Area Index (LAI) as eight days average composited at 1000 m resolution and Digital Elevation Model (DEM) at 30 m resolution were used. Preliminary processing of images was performed using MODIS reprojection tool (MRT) and was converted to a standard format that can be read by MATLAB software. Geo-referencing, subsetting and pixel-wise analysis corresponding to the study area were performed using ArcGIS and ERDAS IMAGINE. Model evaluation was carried out using the following performance measures- coefficient of determination (R2), root mean squared error (RMSE), percent bias (PBIAS) and the intercept (a) and slope (b) terms of a linear regression fit (y = a + bx). Excellent comparisons were obtained between tower measured λET and those estimated by the proposed approach for all four flux tower locations (R2 = 0.85 – 0.96; RMSE = 18.27 – 33.79 W/m2). The proposed methodology was compared with two alternative methods proposed by previous researchers. Performances of all three approaches were comparable indicating the robustness of the methodology proposed in the present study. The PM method proposed in the present study was implemented in the Hemavathi sub-basin which is located in the Cauvery River Basin, Karnataka, India to map spatial patterns of daily AET. MOD16A2 product of actual evapotranspiration (AET) as eight day average composited at 500 m resolution was used for validation purposes. Climate records for the Belur station were used. The analysis was carried out for two dates in summer and two dates in winter separately for the years 2007 (wet year) and 2012 (dry year). For each date, trapezoidal scatter plots of MODIS-derived LST values versus Fr were plotted by considering 1 km2 pixels in the study area of 304 km2. For each day, estimated AET values by the PT approach (AETPT), PM model of the present study with Ga computed using Leuning equation (AETPM) and with Ga computed using Choudhary equation (AETPMCH) for each of the 304 pixels were extracted and compared with the corresponding pixel-wise MOD16A2 ET estimates. Results of the performance evaluation of AET estimation methods relative to MOD16A2 showed that the PM model proposed in the present study with Ga computed using the Leuning equation (AETPM) performed reasonably well for both the wet and dry years. High values of R2 (0.77 – 0.90) and reasonably low values of RMSE (0.28 – 0.38 mm/day) were obtained but the PBIAS values were somewhat high (-7.04 – -12.41). Also, the PM model yielded relatively poorer estimates for the winter days of the drier year 2012. The performance of the PT model was quite similar to the PM model with similar performance statistics being recorded. However, slightly lower RMSE values were obtained for this model on some days. The PM model proposed in the present study with Ga computed using the Choudhary equation turned out to be the best model as indicated by the lowest values of RMSE (0.19 – 0.25 mm/day), although R2 values were similar. Also, use of the Choudhary equation reduced PBIAS values significantly for all days considered. Using the pixel-wise values of AETPMCH, maps showing the spatial variability were prepared for the Hemavathi sub-basin for all the dates considered in 2007 and 2012. The variations of AET over the basin appear to be influenced by topography, type of LU/LC, LST and moisture availability conditions. The satellite-based spatial contextual information approach adopted in the present study for the first time with the PM model has proved to be a simple, calibration-free and accurate method. As demonstrated by previous studies and also the present study, use of the LST-Fr plot does not require additional hydrological data for optimization of the AET model parameters. The framework for implementing the spatial contextual information approach to derive operational estimates of daily AET over large spatial domains has been developed and validated in this study.