Impact of land use changes on hydrological response of humid and sub-humid catchments in Karnataka State, India

Abstract

Due to activities aimed at improving the socio-economic status and wellbeing of people, natural resources are exploited, and, as a result, environment has changed in terms of climate and land use. These changes have great influence on the local hydrologic cycle and hydrologic response of the catchment. In addition to climatic factors, the flow characteristics of a stream depend upon catchment characteristics such as topography, soil, geology and land use and land cover. The land use experiences rapid spatio-temporal changes that become one of the critical factors influencing the pattern of streamflow. The major objective of the present thesis work was to analyze and investigate the interaction between hydrologic response and the land use/land cover (LU/LC) pattern in two contrasting catchments namely Netravati river basin, a humid catchment and Harangi catchment, a sub-humid catchment of Karnataka State, India. This research work was explicitly carried out to: a) perform LU/LC classification and identifying the driving factors using multi-date satellite images, b) prediction of future trends in LU/LC pattern using Land Change Modeler (LCM) and CA-Markov model, c) estimate Actual Evapotranspiration (AET) and Land Surface Temperature (LST) using satellite images, d) explore the applicability of the semi distributed model to estimate streamflow, e) explore the applicability of monthly rainfall-runoff polygon in explaining hydrological processes in humid and sub-humid catchments, and f) analyse the relationship between changes in hydrological response and LU/LC change pattern. Study areas selected for the present work: Netravati river basin and Harangi catchment. The Netravathi basin geographically lies between 75º 01′ E and 75º 46′ E longitude and 12º 29′ N and 13º 11′ N latitude with an area of 3312.74 sq. km. Harangi catchment geographically lies between 750 38’ E and 750 55’ E longitude and 120 24’ N and 120 40’ N latitude with an area of 417.54 sq. km. The study utilized LCM and CA-Markov models for the prediction of LU/LC for the years 2010 and 2016 in Netravati river basin and 2013 and 2016 in Harangi catchment by considering LU/LC maps of 2005, 2007 and 2007, 2010 as base maps respectively. LCM and CA-Markov model predicted the LU/LC change by 2010 with an accuracy of 80.1% and 82.13%, respectively in Netravati river basin. An accuracy of 86.6% and 80% is obtained in Harangi catchment by using LCM and CA-Markov model respectively. The result of land change prediction for theii year 2016 by CA-Markov model in Netravati river basin shows a decrease in forest, fallow land and land with or without scrub land between 2010 and 2016, contributing to an increase in builtup land and plantation. Predicted map of Harangi catchment for the year 2016 shows that the plantation is increasing from 175.77 to 220 sq.km area, but forest, fallow and wasteland are showing a decreasing trend. Then, the present study estimated AET by using Priestley Taylor method based on satellite data in Netravati and Harangi catchments. The Split Window (SW) algorithm was utilized for spatial mapping of LST. Result shows that AET has increased during the study period of 1997-2015. Since the AET estimation method is based on brightness temperature and fractional vegetation cover, the increase in LST and decrease in fractional vegetation cover has lead to increase in AET. The present research work discussed about calibration of continuous hydrological model to predict runoff volume in Netravati river basin. The result of simulation run for the calibration period shows that the model is underestimating peak flows during monsoon and overestimating low flows during summer. The Nash Sutcliffe Efficiency determined for calibration period is about 0.251. This indicates that this model which required 19 parameters seem to be data intensive and necessitated the development of simple methodology to estimate streamflow. Therefore, the study developed a simple methodology to study the hydrological response to changes in two contrasting catchments namely Netravati river basin and Harangi catchment by using rainfall-runoff polygon method. The methodology involved qualitative and quantitative interpretation of runoff coefficient and geometric properties of polygon in relationship with the catchment behavior. Netravati river basin is represented by the less steep and wider polygon indicates the fact that the catchment response to rainfall is variable in each month especially from June to September during all periods. Harangi catchment is characterized by more steep and narrow polygon implies the consistent variation of catchment response to rainfall pattern in each month especially from the end of June to the end of August during all the periods. The analysis concluded that the influence of LU/LC change on rainfall-runoff conversion mechanism is predominant in Netravati river basin when compared to Harangi catchment. This is clearly represented by wider polygon and smaller over all slope of polygon w.r.t x-axis.