Modelling of Basin Wide Daily Evapotranspiration with a Partial Integration of Remote Sensing Data

Vedran Ivezic,Damir Bekic,Bojana Horvat

doi:10.3390/atmos9040120

Abstract

Evapotranspiration (ET) is the most significant water balance component and is also a very complex component to evaluate in spatio–temporal scales. Remotely-sensed data greatly increases the accuracy of basin wide ET estimation but only in periods with available satellite images. This paper describes an attempt to estimate daily ET regardless of the availability of the satellite images. The method is based on application of the interpolated evaporative fraction (Λ) from “historical” satellite images to periods with no satellite data available. Basin wide daily ET is obtained by combining interpolated Λ and standard PET methods on meteorological stations. The reliability of such approach was evaluated by comparing the obtained daily ET to the SEBAL ET estimates through the analysis of residuals (Δ), standard deviations of residuals (σ) and the Nash–Sutcliffe coefficient (NSE) over the basin. The SEBAL ET estimates were validated with the data from two lysimeters. The discrepancy of obtained ET versus the SEBAL ET estimates (Δ = 0.13 mm day−1, σ = 0.64 mm day−1, NSE = 0.07) indicated that the proposed concept has relatively high accuracy, which is notably higher than the Penman–Monteith interpolated ET estimates (Δ = 1.94 mm day−1, σ = 1.03 mm day−1, NSE = −4.71). It was shown that a total of five images can provide a reliable estimate of interpolated Λ and thus represent specific characteristics of a basin. As the presented concept requires minimum remote sensing data and ground based inputs, it could be applied to estimate basin wide daily ET in data scarce regions and in periods with no satellite images available.

Highlights

A discrepancy between water availability and water demand is present continuously and globally, with food production making 70% of all water withdrawals [1]
Remote sensing allows a definition of spatially distributed basin wide actual ET (AET), but with one major drawback: the procedure depends on the usability of the input data in terms of the image quality and the availability of the acquired images
This paper investigated how “historical” remote sensing datasets may be used for basin wide ET

Summary

Introduction

A discrepancy between water availability and water demand is present continuously and globally, with food production making 70% of all water withdrawals [1]. Spatial and temporal variations of available water resources are altered by climate change in many river basins worldwide. Droughts in Europe have incurred a total cost of €100 billion over the past 30 years with a sharp upward trend, so the average costs from droughts have quadrupled [2]. The Mediterranean and the Danube regions in Europe are recognized as being highly vulnerable to droughts [1] with two recent long term droughts, in 2003 and 2015. Evapotranspiration (ET) is major water balance output component in river basins [3,4] and greatly influences the hydrological cycle and the energy balance of the land surface [5]. ET is governed by numerous physical factors and is the most difficult water balance component to measure or to estimate

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Conclusion