Comparing Evapotranspiration Estimates from the GEOframe-Prospero Model with Penman–Monteith and Priestley-Taylor Approaches under Different Climate Conditions

Michele Bottazzi,Antonia Longobardi,Giacomo Bertoldi,Riccardo Rigon,Mirka Mobilia,Marialaura Bancheri

doi:10.3390/w13091221

Abstract

Evapotranspiration (ET) is a key variable in the hydrological cycle and it directly impacts the surface balance and its accurate assessment is essential for a correct water management. ET is difficult to measure, since the existing methods for its direct estimate, such as the weighing lysimeter or the eddy-covariance system, are often expensive and require well-trained research personnel. To overcome this limit, different authors developed experimental models for indirect estimation of ET. However, since the accuracy of ET prediction is crucial from different points of view, the continuous search for more and more precise modeling approaches is encouraged. In light of this, the aim of the present work is to test the efficiency in predicting ET fluxes in a newly introduced physical-based model, named Prospero, which is based on the ability to compute the ET using a multi-layer canopy model, solving the energy balance both for the sunlight and shadow vegetation, extending the recently developed Schymanski and Or method to canopy level. Additionally, Prospero is able to compute the actual ET using a Jarvis-like model. The model is integrated as a component in the hydrological modelling system GEOframe. Its estimates were validated against observed data from five Eddy covariance (EC) sites with different climatic conditions and the same vegetation cover. Then, its performances were compared with those of two already consolidated models, the Priestley–Taylor model and Penman FAO model, using four goodness-of-fit indices. Subsequently a calibration of the three methods has been carried out using LUCA calibration within GEOframe, with the purpose of prediction errors. The results showed that Prospero is more accurate and precise with respect to the other two models, even if no calibrations were performed, with better performances in dry climatic conditions. In addition, Prospero model turned to be the least affected by the calibration procedure and, therefore, it can be effectively also used in a context of data scarcity.

Highlights

The estimation of atmospheric turbulent fluxes at the land surface has long been recognized as the most important issue in the determination of the exchanges of energy and mass among hydrosphere, atmosphere and biosphere (e.g., [1,2,3,4,5,6,7,8])and it is of critical importance to the hydrological and energy cycles [9,10]
As regards the climatic conditions, each of the five main groups selected for the present study is defined by temperature criteria, except for the B climate, which has a low amount of annual rainfall
It is worth noticing that all the calibrated values differ from the literature ones, stressing the importance of using site-specific parameters, when it is possible to perform calibration versus observed data

Summary

Introduction

The estimation of atmospheric turbulent fluxes (sensible and latent heat) at the land surface has long been recognized as the most important issue in the determination of the exchanges of energy and mass among hydrosphere, atmosphere and biosphere (e.g., [1,2,3,4,5,6,7,8])and it is of critical importance to the hydrological and energy cycles [9,10]. The estimation of atmospheric turbulent fluxes (sensible and latent heat) at the land surface has long been recognized as the most important issue in the determination of the exchanges of energy and mass among hydrosphere, atmosphere and biosphere (e.g., [1,2,3,4,5,6,7,8]). ET, and, in particular, its separation in E and T [11], is still difficult to directly measure, and, as reported in [12], current land surface models provide different ratios of the T by vegetation to total ET. Vegetation hydraulic was recently reviewed by Stroock et al [20], providing the idea that a new synthesis is necessary between the modelling of water and carbon fluxes, providing further evidence that an upscaling from cells through plants to landscape is required

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Methods

Results