1 Simulating Climate Change and Socio-economic Change Impacts on Flows and Water Quality 1 in the Mahanadi River System, India 2 Li Jin 1* , Paul G. Whitehead 2 , Harvey Rodda 3 , Ian Macadam 4 , Sananda Sarkar 5 3 4 1 Geology Department, State University of New York College at Cortland, Cortland, NY 13045, 5 USA 6 2 School of Geography and the Environment, University of Oxford, Oxford, UK 7 3 Hydro-GIS Ltd, 10 Coles Lane, Chalgrove, Oxfordshire OX44 7SY, UK 8 4 Met Office, FitzRoy Road, Exeter, EX1 3PB, United Kingdom 9 5 School of Civil Engineering, Kalinga Institute of Industrial Technology, Bhubaneswar, Odisha 10 752024, India 11 * Li Jin li.jin@cortland.edu 12 13 Abstract 14 Delta systems formed by the deposition of sediments at the mouths of large catchments are 15 vulnerable to sea level rise and other climate change impacts. Deltas often have some of the 16 highest population densities in the world and the Mahanadi Delta in India is one of these, with 17 a population of 39 million. The Mahanadi River is a major river in East Central India and flows 18 through Chattisgarh and Orissa states before discharging into the Bay of Bengal. This study uses 19 an Integrated Catchment Model (INCA) to simulate flow dynamics and water quality (nitrogen 20 and phosphorus) and to analyze the impacts of climate change and socio-economic drivers in 21 the Mahanadi River system. Future flows affected by large population growth, effluent 22 discharge increases and changes in irrigation water demand from changing land uses are 23 assessed under shared socio-economic pathways (SSPs). Model results indicate a significant 24 increase in monsoon flows under the future climates at 2050s (2041-2060) and 2090s (2079- 25 2098) which greatly enhances flood potential. The water availability under low flow conditions 26 will be worsened because of increased water demand from population growth and increased 27 irrigation in the future. Decreased concentrations of nitrogen and phosphorus are expected due 28 to increased flow hence dilution. Socio-economic scenarios have a significant impact on water 29 quality but less impact on the river flow. For example, higher population growth, increased 30 sewage treatment discharges, land use change and enhanced atmospheric deposition would 31 result in the deterioration of water quality, while the upgrade of the sewage treatment works 32 lead to improved water quality. In summary, socio-economic scenarios would change future 33