A Modified Gash Model for Estimating Rainfall Interception Loss of Forest Using Remote Sensing Observations at Regional Scale

Yaokui Cui,Li Jia

doi:10.3390/w6040993

Abstract

Rainfall interception loss of forest is an important component of water balance in a forested ecosystem. The Gash analytical model has been widely used to estimate the forest interception loss at field scale. In this study, we proposed a simple model to estimate rainfall interception loss of heterogeneous forest at regional scale with several reasonable assumptions using remote sensing observations. The model is a modified Gash analytical model using easily measured parameters of forest structure from satellite data and extends the original Gash model from point-scale to the regional scale. Preliminary results, using remote sensing data from Moderate Resolution Imaging Spectroradiometer (MODIS) products, field measured rainfall data, and meteorological data of the Automatic Weather Station (AWS) over a picea crassifolia forest in the upper reaches of the Heihe River Basin in northwestern China, showed reasonable accuracy in estimating rainfall interception loss at both the Dayekou experimental site (R2 = 0.91, RMSE = 0.34 mm∙d −1) and the Pailugou experimental site (R2 = 0.82, RMSE = 0.6 mm∙d −1), compared with ground measurements based on per unit area of forest. The interception loss map of the study area was shown to be strongly heterogeneous. The modified model has robust physics and is insensitive to the input parameters, according to the sensitivity analysis using numerical simulations. The modified model appears to be stable and easy to be applied for operational estimation of interception loss over large areas.

Highlights

Rainfall interception loss is the proportion of gross rainfall that is intercepted, stored and subsequently evaporated from all parts of vegetation during or following rainfall
Fractional Vegetation Cover (FVC) due to seasonally dependent photosynthetic activity with the model running at daily steps, daily Vegetation Area Index (VAI) and FVC time series were obtained by linear interpolation of the 8-day time series, based on the assumption that daily VAI and FVC would change linearly between the two products
A RS-Gash model was developed based on the Gash (1995) model to estimate the interception loss of heterogeneous forest using remote sensing observations of forest canopy structure parameters and gross rainfall

Summary

Introduction

Rainfall interception loss is the proportion of gross rainfall that is intercepted, stored and subsequently evaporated from all parts of vegetation during or following rainfall. Many researchers have developed a series of rainfall interception models including: the empirical statistical model [5] and the physically-based model [6,7,8,9,10,11]. The latter has been paid more attention due to its robustness in physics and less need for calibration of empirical coefficients. Applications have covered different types of vegetation including rainforest, conifers, mixed conifer, shrubs, crops, etc Most of these applications, were at field scale [12]

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