Quantitative and Qualitative Perspectives of Forest-Water Interactions at Catchment Scales

Sustaining a resilient and reliable water cycle is a global challenge, which inevitably needs proper understanding and action at many levels. One quarter of the world’s population depends on water from forested catchments, where behavior of atmospheric water nonetheless governs the forest-water interactions and thus the ultimate water availability. As per a coarse estimation the water vapors comprise one quarter of 1% of atmospheric mass being equivalent to just 2.5 centimeters of liquid water over the entire Earth. Such water availability raises more tangible concerns for most people than do temperature and carbon. Ever escalating populations and living standards are badly impacting the earth’s surface in variety of ways, as 1.5 million Km2 of dense tree cover were reported to be lost between 2000-2012, leading to highly impeded access to fresh water. Majority of studies of how forest land use and its change influences climate and hydrology rely on models (mostly imperfect owing to pitiable/incomplete process understandings and poor parameterization). It is projected that land cover changes have caused a 5 to 6 % reduction in global atmospheric wetness. A plethora of alike estimations/inferences are included herein to offer relevant R&D insights on core theme of this paper, by encircling reviews of few global observations and findings towards forest influences on quality and quantity of water. With increasing demand for agricultural and urban land (owing to population/affluent life-styles) majority of forests are put under pressure. At this juncture tropical regions like India remains more crucial, as their water and land use policies are often influenced to big extent by many perceived effects from hydrological functioning of forested catchments. This paper offers certain food for thought by summarizing relevant scientific consensus of key aspects of forest-water relationships and couple of wider aspects towards ‘forest-water interactions’ and ‘water quality and pollution facets. Apprehensions and knowledge gaps about hydrological impacts of forest management and also the emerging futuristic R&D issues are elaborated with specified line of sights on effects of forests and forest management on various stream flow parameters, soil erosion, stream sedimentation, water quality, landslides and water uses. Owing to their inherent capabilities and capacities, the forests govern available moisture for tree growth, evapotranspiration (ET), soil infiltration, ground water recharge, and runoff; hence could be projected as futuristic ‘water towers’. Hydraulic redistribution of water in soil remains other important activities by the forest, where tree root structures plays a vital role to facilitate both upward and downward water dynamics. Even under low to intermediate tree cover each tree remains capable to improve soil hydraulic properties even up to 25 m from its canopy edge, with higher hydrologic gains in comparison to associated additional losses (transpiration and interception). Among most profound and alarming insights offered by this write up are; critical knowledge gaps on understanding importance of forests to water, trends of findings from a few catchments based hydrological experiments on water yield, roles forest may play in regulating water fluxes and rainfall patterns. Other key messages offered for water and forest policy makers includes issues like water use by forests, flood flows, water quality, erosion, climate change, energy forest, and forest water productivities.