Introduction

Water, the elixir of life, sustains the ecological processes and basic needs of all natural processes. Hydro-ecological footprint refers to the hydrological regime that sustains the biotic components of an ecosystem including anthropogenic demand. This emphasizes con-sumption behavior, transactions of resources among/ between ecological and societal activities [1]. Freshwater ecosystems provide numerous ecological services including habitat for diverse species of flora and fauna. However, to sustain the biotic component, ecosystem has to maintain the minimum flows to ensure the quality and diversity. Ecological services provided by a river basin include drinking water, fish, fodder, food, building materials, apart from religious and cultural values. Earlier studies focused on domestic water footprint, production water footprint, and ecological water footprint [2-5]. Domestic water requirement or domestic water footprint considers water required for domestic purposes such as drinking, washing, flushing, cooking, etc. Similarly, production water footprint accounts for water demand by industries, agriculture, horticulture, power generation, and ecological water footprint accounts for water required by an ecosystem. Ecological footprint in general involves water for various aspects such as sustenance of ecosystem, minimal water requirements for aquatic fauna to survive and terrestrial flora in their natural condition. Eco-hydrological footprint assessment entails estimation of carrying capacity of a river basin considering water availability and demand of water for sustenance of biotic components. Carrying capacity deals with sustainable development of human beings and ecological wellbeing [2,6-8]. Figure 1 outlines various components for the sustainability of a region considering resources availability, uses and users needs, and prudent allocation of resources within the ecosystem’s sustainability threshold. Numerous studies of carrying capacities have been carried out considering aspects such as population, agriculture, industries, livestock, water and water bodies, forest, soil, urban, mining, marine, ecotourism, etc. [5,9-18].
Water resource carrying capacity (WRCC†) is defined as the rate at which the resource can be consumed (supportive capacity) and effluents that can be discharged (assimilative capacity) into the environment without affecting the ecological and biological functions, in-tegrity, and productivity [13,19,20]. WRCC provides a theoretical basis and means of operation for sustainable development while accounting for the system’s support-ive and assimilative capacity. Sustenance of hydro-logic regime in a river basin plays a pivotal role in maintaining ecosystem goods and services. It plays a prominent role in the productivity of forest and agriculture goods. This entails maintaining and restoring the ecological health for optimally meeting the demand for water by biotic components.
Uneven spatio-temporal distribution of water re-source across the globe has led to restrictions in water availability across many countries. The United Nations World Water Assessment Programme 2015 [21] predicted that by 2050, the global demand of water would increase by 55 percent, while fresh water resources, either surface or ground water, are depleting due to environmental mismanagement with growing demands of burgeoning population, agriculture, and other socio-economic activ-ities. This would lead to imbalance between water uses and users increasing risk of local conflicts, disruptions in ecosystems, etc. impacting the carrying capacity of the resource.
Natural forest ecosystems in the Western Ghats reg-ulates the transfer of water from the precipitation through the process of evaporation, transpiration, infiltration, and interception [22]. This regulatory mechanism is con-trolled by various physiographic factors such as density, structure, maturity, understory, aerodynamic, surface resistances, root density, root depth, hydro-climatic con-dition, etc. The process of evaporation and transpiration from vegetation, which influences the productivity, water supply, and local climate [23] was the first physiologi-cal process employed in the water budget [24]. Forests through evapotranspiration transfers water to the atmo-sphere [25,26] leading to the formation of rain bearing clouds. Aerodynamically rough surfaces of the forests create turbulence in airflow allowing absorbance of large amounts of solar radiation. The process of evapotrans-piration is controlled by the conductance or resistance along the pathway of water vapor from leaves to the at-mosphere [23]. Canopy cover of forests play a major role in controlling the interception, studies carried out using Rutter Model and Gash models have demonstrated that continuous canopies have low interception whereas inter-mittent canopies have higher interception [27].
The process of infiltration varies with tree density, diversity, and maturity [28,29]. With increasing age of forests, organic matter in soil and micro fauna interac-tion with the roots improves the soil structure, stability, and porosity creating paths for rapid infiltration of water [30]. Increases in monoculture enhance the stream flow significantly [31] during monsoons, and litter forms thick layer reducing infiltration. Plantations containing vege-tation such as Eucalyptus, Acacia, etc. have deeper tap roots due to which the quantum of water drafted from the subsurface region is very high [31], depleting ground water in the basin.
Countries in the tropics are facing imbalances in resource supply and demand with the rapid deforesta-tion [32,33] due to implementation of unplanned de-velopmental activities. Burgeoning population with an