Hydrologic flow regimes in humid tropics river basin Gajendran Chellaiah * and Daniel Biju Eazon Department of Civil Engineering, Karunya Institute of Technology and Sciences, Coimbatore, Tamil Nadu, India *Corresponding author. E-mail: cgajendran@gmail.com GC, 0000-0002-2765-7075 ABSTRACT The study is carried out to understand the impact of the land-use change in terms of alteration in flow regimes, which are understood to be a leading cause of ecological and environmental deterioration in riverine systems. Meenachil river in the humid tropical region of Kerala, India, is one of a kind river with human settlement along the banks for all its 78 kms of flow through the Kottayam District. The analysis of stream- flow from four stream gauge stations was done using Range Variability Approach. The analysis was down as a two-time period analysis with the parametric approach with the period separation taken according to prior studies on land-use change. The analysis shows a high degree of alteration, which can be attributed to the land-use change and can be understood as the root cause for the deterioration of water quality and also the ecological distress, which is well documented in the downstream and watershed regions of the river. Key words: environmental flow, humid Tropics, hydrologic alterations, land-use change, range variability HIGHLIGHTS • Range variability. • Environmental flow. • Land-use change. • Humid Tropics. • Hydrologic alterations. INTRODUCTION Water is the lifeblood of planet Earth (Acreman 2004). The hydro-ecological systems such as lakes, rivers, saline, and freshwater bodies, as well as the groundwaters, are systems that need protection. In the total available water on Earth, which is of 1,400 million km 3 , only 2.5% or 35 million km 3 is freshwater. The primary freshwater sources are the permanent ice caps of Antarctica and Greenland. Another portion is also locked in deep underground aquifers. Lakes, rivers, soil moisture, and shallow ground- water basins are the primary source of usable freshwater. The available and potable volume of freshwater sources is around 200,000 km 3 of water, less than 1% of all freshwater available on Earth (UNEP 2002). The available freshwater renews by rainfall and snowfall at a volume of 40–50,000 km 3 per year. According to UNESCO (2019), the water demand globally was found to be increasing about a percentage from the 1980s, which is caused due to population growth, socio-economic development, and increased consumption. This level of water demand increase is expected to follow the same trend up to 2050. More than 2 billion are expected to be under increased water stress, and another 4 billion people may experience severe water scarcity due to increased consumption and demand. The freshwater crisis is gradually unfolding in India in a significant way. The access to a safe supply of water is in crisis due to the inadequate management of water sources and subsequent destruction to the surroundings. The econ- omic and social development of India is correlated with the water crisis in the country. There is temporal and spatial variation in the water crisis in different parts of India. Due to human action, most of the freshwater ecosystems in India are degrading. The intense competition among the agricultural, industrial, and domestic sectors, which are dependent on groundwater, has left the depletion of groundwater levels. Pollution to the surface water and groundwater has damaged the freshwater quality. Large dams and riverine alteration along with the deforestation and land-use changes along the river banks are threats to the freshwater system. Sand quarrying and riverbank agriculture with land reclamation and construction are This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). © 2021 The Authors Water Science & Technology Vol 00 No 0, 1 doi: 10.2166/wst.2021.357 corrected Proof Downloaded from http://iwaponline.com/wst/article-pdf/doi/10.2166/wst.2021.357/940290/wst2021357.pdf by guest on 29 September 2021