Effectiveness of introducing crop coefficient and leaf area index to enhance evapotranspiration simulations in hydrologic models

Abstract

Evapotranspiration (ET) is an essential component of the hydrological cycle and plays a critical role in water resource management. However, ET is often overlooked in order to transform rainfall to runoff for better streamflow simulation. Hydrological models are commonly used to estimate areal actual evapotranspiration (AET) after calibration against observed discharge. However, classical approaches are often inadequate to appropriately simulate other hydrologic components. Hence, it is important to introduce natural heterogeneity to enhance hydrological processes and reduce water balance errors. In this study, the effectiveness of introducing a constant crop coefficient (Kc), flux tower‐based Kc, and leaf area index (LAI) to three hydrological models (Three‐Parametric Hydrologic Model [TPHM], Génie Rural à 4 paramètres Journalier [GR4J], and Catchment hydrologic cycle Assessment Tool [CAT]) is assessed for the simulation of daily streamflow and AET in a mountainous mixed forest watershed (8.54 km2) in South Korea. The results show that the streamflow simulations after introduction of Kc and LAI to the original models are quite similar. However, the effectiveness of the AET estimation was significantly enhanced after introduction of the flux tower‐based Kc and LAI. The information criterion computed to compare the models reveals that the flux tower‐based Kc‐simulated AET demonstrated better agreement with the observed AET. The Pearson's correlation coefficients (R2) of the TPHM (8%), GR4J (55%), and CAT (55%) models also showed improvements that were greater than the constant based Kc simulation. Similarly, the limitations of the three models with respect to capturing seasonal variation as well as high and low flows were enhanced after the introduction of the flux tower‐based Kc, which adequately reproduced hydrological processes with minimum water balance errors and bias. A regression analysis revealed the potential of estimating Kc as a linear function of LAI (R2 = 0.84). The results of this study indicate that introduction of Kc and LAI to the conceptual rainfall–runoff models can be considered an effective approach to reduce water balance errors and uncertainties in hydrological models and improve the reliability of climate change studies and water resource management.

Improving the Predictive Skill of a Distributed Hydrological Model by Calibration on Spatial Patterns With Multiple Satellite Data Sets

“…Following Demirel et al (), a dynamically scaling function ( F DS ) is used to calculate potential evaporation ( E p ) to account for vegetation‐climate interactions and improve spatial estimation of E p (Bai et al, ; Jiao et al, ). The approach is based on the concept of E p calculation from crop coefficients and E ref (Allen et al, ; Birhanu et al, ). Here the F DS (equation ) plays the role of a spatially varying crop coefficient, and it is estimated based on leaf area index ( I LA ) data.…”

“…It therefore has little discriminatory power to constrain the feasible parameter space of a distributed model, i.e., the boundary flux or closure problem (Beven, 2006b). Consequently, a spatially DHM calibrated only on streamflow is very unlikely able to reproduce a reliable spatiotemporal representation of other hydrological fluxes and states (Birhanu et al, 2019;Clark et al, 2016;Grayson & Bloschl, 2001;Hrachowitz et al, 2014;Livneh & Lettenmaier, 2012;Minville et al, 2014), even if a multiscale parameter regionalization (MPR) scheme is used (Rakovec et al, 2016). Mismatches between temporal and spatial patterns should therefore be expected when comparing hydrological model outputs to other distributed observational data sets (Vereecken et al, 2008;Xu et al, 2014).…”

Suitability of 17 gridded rainfall and temperature datasets for large-scale hydrological modelling in West Africa

“…In this study, the Hargreaves and Samani method (Hargreaves and Samani, 1985), solely based on air temperature data, is used to calculate the reference evaporation (E ref ). Potential evaporation (E p ) is calculated by adjusting E ref to vegetation cover (Allen et al, 1998;Birhanu et al, 2019). A dynamical scaling function (F DS ) (cf.…”

“…The results are presented and discussed for the entire simulation period (2003-2012, i.e. combined calibration and evaluation periods) because reliable meteorological datasets are expected to produce a plausible representation of hydrological processes independently of the modelling period (Bisselink et al, 2016). Separated results are provided for the calibration and evaluation periods in the Supplement.…”

Spatiotemporal changes and driving factors of vegetation in 14 different climatic regions in the global from 1981 to 2018

“…Vegetation growth is dominated by temperature, precipitation, and radiation (Guli•Jiapaer et al 2015, Liang et al 2020. Evapotranspiration is very important in the global hydrological water cycle and energy balance and is an important component of ecological hydrological processes (Birhanu et al 2019, Niu et al 2019. As determined by satellite remote sensing monitoring, the vegetation LAIs are increasing, and the main causes of global greening may be climate change and CO2 fertilization effects (Chen et al 2019).…”