Urbanization and its effects on water resources: Scenario of a tropical river basin in South India

Karamana River Basin (KRB), set in the tropical monsoon climate (i.e., Koppen\u27s Am), hosts the drinking water supply to the capital city of Thiruvanathapuram, one of the highly urbanized cities in the southwestern seaboard of India. Primary focus of the study is a scrutiny of future water security status of KRB, amidst the rising population and subsequent urban sprawl. The study was done through a combination of analysis of remotely sensed data, and collation of data on population growth, surface water distribution and decadal-level groundwater monitoring. An uptrend of the decadal-level population and unscientific constructions across KRB led to the decline of per capita water entitlement and causing conflicts around water service delivery. So this study has an imperative focus on the effects of rapidly growing urban life and its impact on water resources in KRB. This was accomplished by studying the land use, land surface temperature (LST), annual precipitation, and groundwater trend for two decades, followed by land use modeling and quantifying total water deposit. The estimated LST values in KRB, robustly substantiate an upward shift in surface temperature between 2001 (47.55%) to 2020 (64.01%), a testimony of urban sprawl and it may be the major cause to reduce the rate of rainwater infiltration and increase in runoff. The Normalized Difference Vegetation Index (NDVI), used to generate land use map, and LST of the basin have been assessed for the years 2001, 2011, and 2020 to model whether or not land use has been modulated by urbanization. Based on this, future trends of land use changes for 2030 and 2050 have been predicted using CA-Markov model - a model combining Cellular Automata and Markov chain. We also carried out a quantification of annual water deposit, potential evapo-transpiration, infiltration, surface runoff, and storage. Decadal trends of population change, degree of urbanization and consequent rise in domestic water demand and shrinkage of area of open space/soil cover have also been factored in assessing water security in KRB. The results show that, as of today, the city is facing an acute annual shortage of surface water by 321.51 MCM. Furthermore, we propose potential sources for future water security of the state\u27s capital region