Preliminary Investigations on Localized Rainfall Interception Losses Under Real Field Observations

Abstract

Even under prevailing advanced science era, hydrological loss functions remain the weakest link and thus governs the ultimate success of any rainfall-runoff modeling on natural catchments. Among various such loss functions, interception happens to be the first and foremost element, on which research efforts are almost negligible, being truer for India and particularly middle Gujarat region. Present study is a preliminary effort, where field-based experimentations were conceived and conducted during rainy season of 2014, by adopting natural trees of different varieties and equipping them with certain low-cost alternative simple gauging setups to record daily magnitudes of stemflows, throughfalls and rainfalls. Two diverse sites were earmarked at newly developed College of Agricultural Engineering and Technology (CAET) Godhra in Gujarat, encompassing about 40 trees of 13 different types/varieties at 2 different sites. Simplified standard protocols and methodological steps were adhered, for measuring the stemflows, throughfalls, and actual rainfalls during active monsoon. Canopy interception (daily) was determined along with stemflow, by equipping the tree barks with reused half-cut tires and flexible plastic pipes and containers beneath it. Appropriately measured tree canopy area and rainfall were utilized in computations. Preliminary results as obtained and communicated herein are indeed an effort to visualize and attempt gap filling for this mistreated hydrological component. The observed range of average values of stemflows and throughfalls was found extremely heterogeneous depending upon rainstorms as well as physiological attributes of trees (8-20 and 5-35%, respectively). Though the individual observed values of intercepted rains remained small, but their cumulative magnitudes had visible hydrological impacts (soil moisture patterns, infiltration patter, overland flows, and re-distribution of raindrops) on land surface located beneath the tree canopy. Results revealed significant influences of vegetative physiognomies on several such impacts from intercepted rainfall, owing to heterogeneous trees and their physiological architecture (canopy area, tree height, types and shape of leaves, bark/branches). The qualitative analysis of intercepted rainwater was also performed and reported herein. Larger trees such as azadirachta indica (neem), mangifera indica (mango), tamarind (emlee), Saraca asoca (ashoka) showed higher interception magnitudes, even for identical rains, showing influence of their high aerodynamic roughness. The observed magnitudes and patterns of rainfall interception from this study are expected to be of vital utilities for futuristic hydrological modeling efforts in study region.