1. Ph.D Theses
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/1/11
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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 Characterization Of Historical and Future Hydrometeorological Droughts in an Indian Tropical River Basin(National Institute of Technology Karnataka, Surathkal, 2020) Pathak, Abhishek A.; Dodamani, B M.Drought is acknowledged as a significant natural disaster which leads to food, fodder, and water shortages along with destruction of vital ecological system. Drought is a transient recurring sinister disaster, which originates from the lack of precipitation and further creeps into different subdivisions of hydrological cycle causing adverse effects on agricultural and its allied sector. Combination of these leads to economic losses and several damage to living organisms. Identifying and quantifying drought characteristics of a region is must to understand the behavior of drought and its profound impacts on society, economy, and environment. Along with the historical knowledge, comprehensive overview of future drought projections is a vital step in ensuring future water and food security. The present study focuses on characterizing different hydrometeorological droughts in the historical and future climate of an agrarian Indian river basin. The specific objectives of the study are 1) To investigate annual and seasonal trends of hydro meteorological variables, over the study area. 2) Assessment and comparison of Meteorological, Hydrological and Agricultural drought characteristics with multiple indices 3) To explore the applicability of copulas theory for joint modeling of drought characteristics 4) Characterization of future hydro-climatic droughts. The study was implemented in the Ghataprabha river basin, being one among the potential lands for agriculture in the basin of river Krishna. Firstly, the basin has been categorized in to humid, sub humid and semiarid region based on Aridity Index. Similarly, groundwater well of the study area are grouped in to different clusters using hierarchical and non-hierarchical clustering methods The annual and seasonal trend analysis of different hydrometeorological variables are carried out using Mann-Kendall trend test and the magnitude of the trend was estimated using the Sen’s Slope Estimator. A non-significant decreasing trends in both rainfall and rainy days was observed in semiarid region during monsoon period. Significant increasing trend in mean temperature was observed for all the stations and for all the seasons with the average magnitude of 0.2⁰ C per decade. Along with the mean temperature, annual andseasonal PET trends were also increasing for all the stations but are significant only in semiarid region with the average increase of 3.5mm per decade. The trends in annual streamflow of the basin are decreasing with magnitude of 574.25 cumecs/year, whereas, no significant trends were observed in the reservoir levels. The trend analysis of the groundwater levels of different clusters, revealed that annual water level in the 81% of the wells of cluster 2 and 47% of the total wells of the study area are significantly declining. The hydrometeorological droughts assessment with different indices portrayed significant number of droughts in the past. The RDI and SPI are behaving similarly in all the stations whereas, significant discrepancies was observed between SPI/RDI and SPEI. The hydrological drought assessed with SDI followed similar pattern with SRSI whereas it showed significant divergence with meteorological droughts. Similarly, Agricultural drought derived through VCI followed similar pattern of SPI-6 in comparison with SPI-3. A teleconnection between meteorological drought and groundwater drought was observed along with the crucial role of underlying hydrogeological characteristics. Joint modelling of hydrometeorological drought characteristics and regional bivariate frequency analysis was carried out by employing Archimedean copula. An attempt has also been made to characterize drought in multivariate perspective by developing Standardized Hydro Meteorological drought Index. From the results of bivariate frequency analysis of meteorological drought, it was observed that, droughts of high severity with prolonged duration are frequent in semiarid region compared to humid and sub-humid regions. The joint probability of hydrological drought conveyed drought of smaller duration or severity are more prominent in the basin whereas joint return periods of groundwater drought is high in the well of cluster 2. The developed SHMI considers combined effects of precipitation and streamflow to picturize a near realistic drought scenario of the basin. The future hydrometeorological drought characteristics were assessed by different RCMs. The different bias correction methods were applied to rainfall and temperature to raw RCMs and observed that CNRM-CM5 with LS bias correction method performed better for correcting the rainfall and VS is proved to be superior for correcting the temperature projections. The trend analysis carried out for the future hydrometeorological variable showed significant decreasing trends in annual and post monsoon season whereas temperature trend is increasing significantly with the rise of 0.150 C per decade. The future hydro-meteorological drought characteristics revealed that the basin will experience more number of droughts compared to the past and it can be attributed to decreasing rainfall trend and significant rise in temperature of the basin. In this study, an attempt has been made to characterize future and historical hydrometeorological droughts comprehensively. The outcome of the study will be helpful to design proactive drought mitigation and preparedness strategies for upcoming drought and it also provides a framework to evaluate the drought risks at other parts of the world.Item Assessment of Climate Change Impacts on River Basins Originating in the Western Ghats of India(National Institute of Technology Karnataka, Surathkal, 2018) Amogh Mudbhatkal; Amai MaheshaThe Western Ghats of India are an environmental and climate-sensitive region of India. The Western Ghats are the mountainous forest range of tropical region which plays a major role in the distribution of Indian monsoon rains. The present study was focused on the assessment of climate change impacts on the hydrology of river basins originating in the Western Ghats of India. Nine river catchments across the Western Ghats were selected to represent the complete range of spatial, topographical and climate variability. The study was carried out with four objectives which include (i) Analysis of historical trends in rainfall, temperature, evapo-transpiration, and streamflow, (ii) Performance evaluation of bias correction methods for precipitation and temperature with regard to hydrological modeling, (iii) Simulation of catchment response under forecasted climate conditions by using the Soil and Water Assessment Tool (SWAT) hydrological model, and, (iv) Examination of dependence of streamflow on elevation and suitability of regional network of weather stations and river gauges for predicting hydrological impacts of climate change. The data used in the study were procured from India Meteorological Department (historical meteorological data), Rossby Centre Regional Climate Model - RCA4 (RCP 4.5 forecasted meteorological data), and India Water Resource Information System (river gauging data). The frequency analysis was also carried out on the river flow to obtain flow quantiles at 10% duration intervals in the range 10% - 90%. The High flow index (HFI) (Q10/Q50) and the Low flow index (LFI) (Q90/Q50) were derived from the flow quantiles. The HFI was used to characterize the relative magnitudes of peak flow (Q10) with reference to the median flow (Q50), while the LFI was used to characterize relative magnitudes of low flow (Q90) to the median flow. The trend analysis was performed using the modified Mann-Kendall trend test and the magnitude of the trend was estimated using the Sen’s Slope Estimator. The analysis was carried out for scenarios: Scenario 1 (1951-2005; historical data) and Scenario 2 (2006-2060; forecasted data). The trend analysis of historical data revealed that the effect of climate change in the river basins of Western Ghats of India is quite heterogeneous and the central and southern portions of the Western Ghats are more vulnerable to the climate change. The annual rainfall was found to increase over central rivers (Malaprabha and Aghanashini) by 4% and 3.5% per decade, respectively. The annual rainfall over southern rivers, Netravathi and Vamanapuram decreased by 3% and 4.3% per decade. The southern rivers indicated a weakening of the Indian South-west monsoon as monsoon rainfall decreased at the rate of 3.2%, 2.3%, and 6.2% per decade over Netravathi, Chaliyar, and Vamanapuram river catchments, respectively. However, the post-monsoon and summer rainfall was found to be increasing. No improvement was noticed in the forecasted scenario. The historical temperature was found to be increasing with average annual temperature rising to the extent from 0.02 °C to 0.12 °C per decade. The southern river catchments witnessed the highest increase in average annual temperature (0.12 °C per decade in Vamanapuram catchment) and it was found that the southern river catchments are warming more rapidly as compared to the northern river catchments. Upon analysis of the seasonal temperature, the increase during monsoon season was the highest followed by the summer season. The forecasted scenario indicates a higher rate of increase in annual and seasonal temperature. The monsoon and summer season could witness an increase at the rate of 0.14 °C per decade. The potential evapo- transpiration indicates an increasing trend over several catchments, as a consequence of rising temperature. The streamflow in the rivers was found to be decreasing by as much as 17.50% annually in the southern rivers followed by 12% and 4% decrease in central and northern rivers, respectively. The river Aghanashini in the central portion of the Western Ghats of India demonstrated better resilience to climate change. The bias correction methods adopted and compared in this study were the Linear Scaling (LS), Delta Change Correction (DC), Local Intensity (LI) scaling, Power Transform (PT), Variance Scaling (VS), and the Distribution Mapping (DM) method. These six methods may be classified into five bias correction methods applied for precipitation (LS, DC, LI, PT, and DM) and four methods for temperature (LS, DC, VS, and DM). The results indicated that the raw-RCM simulated precipitation is biased by 42% and the temperature is biased by 12% across the catchments investigated. Subsequently, a bias of 65% was found in the streamflow. This was attributed to underestimation of heavy precipitation and overestimation of light precipitation events and precipitation frequencies, by the RCM. The DC method significantly improved the rainfall and temperature time series for the catchments. The hydrologic modeling using the bias-corrected data forced on SWAT hydrological model showed the superiority of DC method. The performance of the delta change correction method was consistently better for precipitation (with NSE >0.75 for 5 catchments) and temperature (NSE = 1) compared to other methods. Good performance was observed between the observed and bias corrected streamflow (daily time scale) for the catchments Purna (NSE = 0.97), Ulhas (NSE = 0.64), Aghanashini (NSE = 0.82), Netravathi (NSE = 0.89), and Chaliyar (NSE = 0.90), low performance with NSE of 0.3 was observed for catchments Kajvi and Vamanapuram. The methods failed for Malaprabha and Tunga catchments. This work concludes that, the delta correction method is the most appropriate method of bias correction for the impact analysis of climate variables for the catchments of the Western Ghats. The examination of dependence of rainfall and streamflow on elevation stratification revealed that the lag time between the rainfall event and resulting runoff was proportional to elevation stratification (10, 20, and 30 days in Zone 1, 2, and 3, respectively for river Aghanashini). Also, the maximum intensity of rainfall over the west-flowing rivers of the Western Ghats of India is at some distance from the crest on the windward side. In the east-flowing rivers, the maximum rainfall is at the crest and decreases on the leeward side from the Western Ghats. The impacts of climate change on the local response to streamflow pattern was found to be varying and the availability of water in the month of May was higher compared to previous decades. The number of rainy days (rainfall>2.5mm/day) was lesser in the northern catchments and higher in the central and southern catchments indicating that, the central and southern portions of the Western Ghats receive more events of rainfall, but the intensity of rainfall is decreasing over time. The major contributing months for monsoon rainfall are June-July and the second half of monsoon (August and September) are witnessing a decrease in rainfall. Compared to conventional peak streamflow availability during July and August, the peak streamflow availability is higher during July as a response to such changing rainfall pattern. The variation in annual streamflow availability is less in the northern rivers and decreasing in the southern rivers. The frequency analysis suggests more Q10 flows in central rivers (Malaprabha, Aghanashini, and Tunga) and lesser Q10 and Q90 flow in the southern rivers (Netravathi, Chaliyar, and Vamanapuram). The High Flow Index (HFI) slightly increased in the northern rivers and magnitude of increase was higher in central rivers. The HFI decreased in the southern rivers and accordingly, the Low Flow Index (LFI) increased. The present work is an attempt to comprehensively study the climate change and its impact on rivers of the Western Ghats of India. The work is an effective tool in understanding the hydrological impacts of climate change and adopting strategies to counter the impacts of climate change.