Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Hydrol. Earth Syst. Sci., 21, 4449-4467, 2017
https://doi.org/10.5194/hess-21-4449-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
07 Sep 2017
An improved SWAT vegetation growth module and its evaluation for four tropical ecosystems
Tadesse Alemayehu1,2, Ann van Griensven1,2, Befekadu Taddesse Woldegiorgis1, and Willy Bauwens1 1Vrije Universiteit Brussel (VUB), Department of Hydrology and Hydraulic Engineering, Brussels, Belgium
2IHE Delft Institute for Water Education, Department of Water Science and Engineering, Delft, the Netherlands
Abstract. The Soil and Water Assessment Tool (SWAT) is a globally applied river basin ecohydrological model used in a wide spectrum of studies, ranging from land use change and climate change impacts studies to research for the development of the best water management practices. However, SWAT has limitations in simulating the seasonal growth cycles for trees and perennial vegetation in the tropics, where rainfall rather than temperature is the dominant plant growth controlling factor. Our goal is to improve the vegetation growth module of SWAT for simulating the vegetation variables – such as the leaf area index (LAI) – for tropical ecosystems. Therefore, we present a modified SWAT version for the tropics (SWAT-T) that uses a straightforward but robust soil moisture index (SMI) – a quotient of rainfall (P) and reference evapotranspiration (ETr) – to dynamically initiate a new growth cycle within a predefined period. Our results for the Mara Basin (Kenya/Tanzania) show that the SWAT-T-simulated LAI corresponds well with the Moderate Resolution Imaging Spectroradiometer (MODIS) LAI for evergreen forest, savanna grassland and shrubland. This indicates that the SMI is reliable for triggering a new annual growth cycle. The water balance components (evapotranspiration and streamflow) simulated by the SWAT-T exhibit a good agreement with remote-sensing-based evapotranspiration (ET-RS) and observed streamflow. The SWAT-T model, with the proposed vegetation growth module for tropical ecosystems, can be a robust tool for simulating the vegetation growth dynamics in hydrologic models in tropical regions.

Citation: Alemayehu, T., van Griensven, A., Woldegiorgis, B. T., and Bauwens, W.: An improved SWAT vegetation growth module and its evaluation for four tropical ecosystems, Hydrol. Earth Syst. Sci., 21, 4449-4467, https://doi.org/10.5194/hess-21-4449-2017, 2017.
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Short summary
The goal of this paper is to improve the vegetation growth modelling in SWAT for tropical ecosystems. Therefore, we propose a straightforward but robust soil moisture index (SMI) – a quotient of rainfall (P) and reference evapotranspiration (ETr) – to dynamically initiate a new growth cycle within a predefined period. Our results for the Mara Basin (Kenya/Tanzania) show that the simulated LAI corresponds well with the MODIS LAI for for evergreen forest, savanna grassland and shrubland.
The goal of this paper is to improve the vegetation growth modelling in SWAT for tropical...
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