Assessment of rainfall interception, soil moisture dynamics and seasonal headwaters in a micro-catchment of Western ghats

Abstract

The aim of this study is to assess the canopy rainfall interception, surface detention storage, and soil moisture fluctuation in a micro-catchment of a coffee plantation. Field measurements were carried out using 15 funnel-type ordinary rain gauges in an experimental area of 30 m × 30 m to measure the rainfall passing through the upper and lower canopy to estimate interception and throughfall. Rain gauges were placed at different locations to account for variability in net rainfall falling over the catchment. Throughfall measurements were compared with Gross rainfall measurements taken in an open space near to the plot. The overall ratio of the average of net ground precipitation to gross rainfall measured at the open space for the season was 0.82. Analysis for different rainfall intensities showed that lower-intensity rainfall contributes a higher fraction of the rainfall to interception loss. Site-specific field-based equations have been developed to convert the rainfall into throughfall for the agrarian basins of coffee plantations. Soil moisture depletion data revealed that the upper layer of the soil responds to rainfall and atmospheric demand quickly, compared to the deeper soil layers. Thick soil layers require a longer duration to reach field capacities and contribute significant amounts of the flow in seasonal/low-order streams. The discharge measurements after two months of continuous rainfall revealed that soils in plantation fields reach saturation during the monsoon season and release water to maintain flow in non-perennial streams after the monsoon season ends.