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Enhancing SWAT with remotely sensed LAI for improved modelling of ecohydrological process in subtropics

Ma, Tianxiao ; Duan, Zheng LU ; Li, Runkui and Song, Xianfeng (2019) In Journal of Hydrology 570. p.802-815
Abstract

Vegetation growth in Soil and Water Assessment Tool (SWAT) is a crucial process for quantifying ecohydrological modelling, as it influences evapotranspiration, interception, soil erosion and biomass production. The simplified version of Environmental Policy Integrated Climate (EPIC) in SWAT was originally designed for temperate regions and naturally based on temperature to simulate growth cycles of vegetation. However, tropical or subtropical vegetation growth is mainly controlled by rainfall. Due to this limitation, current SWAT simulations in tropics and subtropics have been facing a series of problems on vegetation dormancy, water balance and sediment yield. Therefore, we proposed an approach to enhance... (More)

Vegetation growth in Soil and Water Assessment Tool (SWAT) is a crucial process for quantifying ecohydrological modelling, as it influences evapotranspiration, interception, soil erosion and biomass production. The simplified version of Environmental Policy Integrated Climate (EPIC) in SWAT was originally designed for temperate regions and naturally based on temperature to simulate growth cycles of vegetation. However, tropical or subtropical vegetation growth is mainly controlled by rainfall. Due to this limitation, current SWAT simulations in tropics and subtropics have been facing a series of problems on vegetation dormancy, water balance and sediment yield. Therefore, we proposed an approach to enhance the modelling of SWAT vegetation dynamics with remotely sensed leaf area index (LAI), to finally increase the applicability of SWAT in tropical or subtropical areas. Spatially and temporally continuous LAI products (1 day, 500 m) from Moderate Resolution Imaging Spectroradiometer (MODIS) observations were integrated into SWAT to replace the LAI simulated by built-in EPIC module. Two advanced filter algorithms were employed to derive a downscaled LAI (30 m) to keep a consistent spatial scale with the size of Hydrological Response Units (HRU) and open data (i.e. SRTM, 30 m), and the source code of the plant growth module were correspondingly modified to incorporate the downscaled LAI into SWAT. To examine the performance of our proposed approach, a case study was conducted in a representative middle-scale (6384 km 2 ) subtropical watershed of Meichuan basin, China, and detailed analysis was performed to investigate its ecohydrological effects, such as streamflow, sediment yield and LAI dynamics from 2001 to 2014. Model performances were compared among three scenarios: (1) original SWAT, (2) SWAT with a corrected plant dormancy function, and (3) modified SWAT after integration of MODIS LAI (our proposed method). Results showed that the modified SWAT took advantage of downscaled MODIS LAI and produced more reasonable seasonal curves of vegetation cover factor (C) of plants than the original model. Correspondingly, the modified SWAT substantially improved streamflow and sediment simulations. The findings demonstrated that SWAT model can be a useful tool for simulating ecohydrological process for subtropical ecosystems when integrated with our proposed method.

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publishing date
type
Contribution to journal
publication status
published
subject
keywords
Integration, LAI, Modified SWAT, MODIS, Subtropics, Vegetation growth
in
Journal of Hydrology
volume
570
pages
14 pages
publisher
Elsevier
external identifiers
  • scopus:85060989490
ISSN
0022-1694
DOI
10.1016/j.jhydrol.2019.01.024
language
English
LU publication?
no
id
1a10dda1-0aa9-4db5-8932-9b3f2ed2a718
date added to LUP
2019-12-22 20:10:03
date last changed
2020-10-07 06:49:45
@article{1a10dda1-0aa9-4db5-8932-9b3f2ed2a718,
  abstract     = {<p>                             Vegetation growth in Soil and Water Assessment Tool (SWAT) is a crucial process for quantifying ecohydrological modelling, as it influences evapotranspiration, interception, soil erosion and biomass production. The simplified version of Environmental Policy Integrated Climate (EPIC) in SWAT was originally designed for temperate regions and naturally based on temperature to simulate growth cycles of vegetation. However, tropical or subtropical vegetation growth is mainly controlled by rainfall. Due to this limitation, current SWAT simulations in tropics and subtropics have been facing a series of problems on vegetation dormancy, water balance and sediment yield. Therefore, we proposed an approach to enhance the modelling of SWAT vegetation dynamics with remotely sensed leaf area index (LAI), to finally increase the applicability of SWAT in tropical or subtropical areas. Spatially and temporally continuous LAI products (1 day, 500 m) from Moderate Resolution Imaging Spectroradiometer (MODIS) observations were integrated into SWAT to replace the LAI simulated by built-in EPIC module. Two advanced filter algorithms were employed to derive a downscaled LAI (30 m) to keep a consistent spatial scale with the size of Hydrological Response Units (HRU) and open data (i.e. SRTM, 30 m), and the source code of the plant growth module were correspondingly modified to incorporate the downscaled LAI into SWAT. To examine the performance of our proposed approach, a case study was conducted in a representative middle-scale (6384 km                             <sup>2</sup>                             ) subtropical watershed of Meichuan basin, China, and detailed analysis was performed to investigate its ecohydrological effects, such as streamflow, sediment yield and LAI dynamics from 2001 to 2014. Model performances were compared among three scenarios: (1) original SWAT, (2) SWAT with a corrected plant dormancy function, and (3) modified SWAT after integration of MODIS LAI (our proposed method). Results showed that the modified SWAT took advantage of downscaled MODIS LAI and produced more reasonable seasonal curves of vegetation cover factor (C) of plants than the original model. Correspondingly, the modified SWAT substantially improved streamflow and sediment simulations. The findings demonstrated that SWAT model can be a useful tool for simulating ecohydrological process for subtropical ecosystems when integrated with our proposed method.                         </p>},
  author       = {Ma, Tianxiao and Duan, Zheng and Li, Runkui and Song, Xianfeng},
  issn         = {0022-1694},
  language     = {eng},
  month        = {03},
  pages        = {802--815},
  publisher    = {Elsevier},
  series       = {Journal of Hydrology},
  title        = {Enhancing SWAT with remotely sensed LAI for improved modelling of ecohydrological process in subtropics},
  url          = {http://dx.doi.org/10.1016/j.jhydrol.2019.01.024},
  doi          = {10.1016/j.jhydrol.2019.01.024},
  volume       = {570},
  year         = {2019},
}