An Assessment of Climatic and Anthropogenic Impacts on the Hydrological System of Himayat Sagar Catchment, India
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An Assessment of Climatic and Anthropogenic Impacts on the Hydrological System of Himayat Sagar Catchment, India Rajesh Nune July, 2018 Submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy Department of Infrastructure Engineering The University of Melbourne i Declaration This is to certify that: 1. The thesis comprises only my original work towards the PhD except where indicated in the preface, 2. Due acknowledgment has been made in the text to all other material used, 3. The thesis is less than 100,000 words in length, exclusively of tables, maps, bibliographies and appendices Rajesh Nune July, 2018 ii Abstract Many regions of the world face water shortages that are likely to become more severe in the future. Multiple drivers are responsible for the hydrological change in catchments and these can be exogenous (change in climate variability and mean), endogenous (anthropogenic changes in catchment characteristics) or both. Water shortages, especially streamflow and groundwater storage, lead to impacts on water users within and outside the catchment, which are typically more severe for downstream users. Both exogenous and endogenous changes can have a large impact on catchment hydrology and they need to be considered together. This research aims to understand such changes in the Himayat Sagar (HS) catchment, India, where significant reductions in streamflow and declining groundwater storage have been observed for a couple of decades. This thesis aims first, to examine different changes that have taken place in HS climate and catchment characteristics, apply statistical, conceptual and hydrological modelling approaches to relate and attribute the observed changes to the trends in both the streamflow and groundwater storage and then examine potential future changes through scenario analysis. To support that analysis a field investigation was undertaken to collect information on various catchment characteristics. An analysis of the available data showed that HS streamflow has declined at a rate of 3.6 mm/y without significant changes in rainfall, over the period 1980 to 2007. Analysis indicated that evapotranspiration from the catchment have increased significantly due to landuse change. Different approaches to estimate evaporation based on the different catchment changes were used. Evapotranspiration estimates based on well inventories suggested an increase of 7.2 mm/y, whereas changes in irrigation area combined with typical irrigation practices suggests applied water increased by 9.0 mm/y. Estimates of evapotranspiration using remote sensing data showed an increasing rate of 4.1 mm/y. Changes in surface water storage capacity and interception of various small watershed development structures have also occurred and these increased by 2 mm over 7 years. These changes have likely increased recharge while reducing the streamflow of the catchment. Overall, the expansion of agricultural irrigation area led to an increase in groundwater extractions and decrease in iii groundwater levels, which effected the contribution of groundwater discharge (baseflow) to streamflow of the HS catchment. The second major analysis step aimed to detangle the individual and combined impacts of HS climate and catchment changes on hydrology in the past through modelling. A coupled semi- distributed surface and groundwater model, the Modified SWAT was used to model the hydrologic impacts of changes in Himayat Sagar catchment characteristics. The model was able to predict the trends in streamflow and groundwater levels well. Simulations including various subsets of catchment changes were used to separate different impacts; notably changes in hydrological structures that aim to intercept runoff and increase recharge, changes in land use, especially irrigation expansion and changes in meteorological forcing. A reduction in average annual simulated streamflow for the validation period of 2 mm or less was found when hydrological structure changes were added into a simulation. Nearly 50% of the total amount of water harvested by the hydrologic structures ultimate contributed to simulated streamflow as baseflow from the groundwater storage. Land use change and associated water extractions led to an increase of 44 mm in simulated catchment average annual irrigation amount. Which led to a net water withdrawal of 25 mm and to a decrease in streamflow of 19 mm, primarily baseflow (15 mm). Groundwater storage declined at a rate of 5 mm/y due to land use impacts and this was offset by a net addition of 2 mm/y by hydrological structures. Overall the simulations suggest that the land use change impacts on streamflow are an order of magnitude larger than the impact of hydrological structures and about 2.5 time higher in terms of groundwater impacts. The total irrigation requirement, which is met by groundwater extraction, was completely met by recharge during the wet years. During the remainder of the time, (dry and normal years), the irrigation requirement was met from a combination of recharge and existing groundwater storage (50% during dry years and 30% during normal years). Overall this is leading to moderate and unsustainable declines in groundwater over time. Finally, to examine the relative impacts of potential future land and water management changes and climate change on the catchment hydrologic cycle and its sustainability, a scenario analysis was undertaken. Providing REgional Climates for Impacts Studies – a iv Regional Climate Model (PRECIS RCM) future climate data was used to analyse the impact of future climate changes on streamflow and groundwater storage of HS catchment. The water storage capacity of large village drinking water storage tanks and naturally formed lakes were assumed to increase by 50% by 2020 and then remain the same until the end of the century (2098). This reflects a program referred to as Mission Kakateeya, which started in 2015 in Telangana State to rejuvenate or desilt existing village water tanks to increase the capture of rainwater over the next five years, i.e by 2020. The irrigated area in the catchment was assumed to increase at the rate of 100 km2 for every 30 years by assuming that the government of Telangana would continue to subsidise farmers, whereas past growth rates have been higher (1990-2000: 85 km2; 2000-2010: 95 km2, an average of 90 km2). Irrigation is assumed to be supported by groundwater alone. Given that the HS catchment falls in a drought prone area of India, it was also assumed that the watershed development program would continue in the future, and therefore that the water storage capacity of small watershed structures would continue to increase at a constant rate over the study period. Capacity was assumed to increase 2km2 by 2040, 4km2 by 2070 and 1.7 km2 by 2098. During early-century, streamflow were predicted to reduce by an average of 49%, increases AEt by 20% and groundwater storage decreases by 3 m across the catchment compared to the baseline period. During mid-century, streamflow were predicted to decrease by 64%, AEt increases by 36% and groundwater storage declines by 7 m compared with the baseline period. During end-century, streamflow were predicted to decrease by 65%, AEt would increase by 45%, and groundwater storage could decrease by 10 m and stores will increase from -8 to 3 mm as compared to baseline period. The contribution of base flow to streamflow plays a key role in the future, it is observed that the base flow contribution is around 20-30% during low rainfall events and 60-70% during high rainfall events as compared with baseline period. v Preface This thesis presents the research carried out during my PhD candidature in the Department of Infrastructure Engineering, The University of Melbourne. The material included here has not been submitted for any other qualification. The thesis comprises only my original work towards my PhD. Chapter 4 has previously been published in Water Resources Management in 2014. The paper presents part of my PhD work and was written by myself. Prof. Andrew. W. Western and Dr B. George provided ideas, discussion and supervision during the research and co-authored the paper. Dr. P. G. Teluguntla assessed the trend of Evapotranspiration in the study and co- authored the paper. 1R., Nune, B., George, P., Teluguntla, and A.W., Western, (2014), Relating trends in streamflow to anthropogenic influences: A case study of Himayat Sagar catchment, India, Water Resources Management, volume 28, Issue 6 (2014), Page 1579-1595, doi. 10.1007/s11269- 014-0567-5 vi Acknowledgments This research is funded by the Australian Centre for International Agricultural Research (ACIAR), Australia through a John Allwright Fellowship Award. The research includes a field survey in the study area, which was supported by a Robert Bage Memorial Scholarship, from the University of Melbourne, Australia. Thanks are due to the International Water Management Institute (IWMI), ICRISAT, Hyderabad for the working space provided during field work in India. Thanks are also due to all the Indian and Telangana State Government Departments mentioned in the chapters for providing their valuable data for conducting this research. I owe special gratitude to my both supervisors Prof. Andrew Western and Dr. Biju George for their conscientious supervision, expert advice and kind support, which facilitated successful completion of my thesis. I also thank them for the opportunities afforded me for tutoring, research assistantship, attending international conferences and training, which made me notably stronger in subjects, more confidant in many areas such as hydrological modelling, analytical and critical thinking, skills for research, professional development in terms of better academic writing, presentation and better management skills. My sincere thanks also go to the Research Committee members, Prof. Hector Malano and Dr. Murray Peel for their constructive and insightful suggestions on my research work. I would also like to thank Dr. Tim Peterson and Dr. Bandara Nawarathna for their valuable suggestions and discussions on surface and groundwater models. I owe my special thanks to Dr Judy Dunai, for her great support in improving the Thesis write up.