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Can the introduction of the topographic indices in LPJ-GUESS improve the spatial representation of environmental variables?

Narváez Vallejo, Alejandra LU (2016) In Master Thesis in Geographical Information Science GISM01 20152
Dept of Physical Geography and Ecosystem Science
Abstract
Ecosystem modelling is an always evolving science trying to catch the complexity of the nature and its principles to model environmental responses in a realistic way. Over and over, models try to introduce more variables and interactions to achieve better representations of phenomena of interest like the responses of the ecosystem to a fast changing world (climate change, land use change). LPJ-GUESS is a flexible dynamic ecosystem model widely used to model the structure and dynamics of terrestrial ecosystems. It is based on plant physiology, biochemical cycles and feedbacks on independent gridcells, there is no consideration of lateral transfer of water between cells. On the other hand, soil moisture is essential for vegetation growth and... (More)
Ecosystem modelling is an always evolving science trying to catch the complexity of the nature and its principles to model environmental responses in a realistic way. Over and over, models try to introduce more variables and interactions to achieve better representations of phenomena of interest like the responses of the ecosystem to a fast changing world (climate change, land use change). LPJ-GUESS is a flexible dynamic ecosystem model widely used to model the structure and dynamics of terrestrial ecosystems. It is based on plant physiology, biochemical cycles and feedbacks on independent gridcells, there is no consideration of lateral transfer of water between cells. On the other hand, soil moisture is essential for vegetation growth and its distribution is known to be driven by the topography of the landscape, which drives the lateral transfer of water. Based on this, it was considered important to assess the modelled spatial representation of environmental variables (soil moisture, LAI) from LPJ-GUESS and to evaluate a possible method to include the effect of topography over the hydrology in LPJ-GUESS model. For this, Alergaarde catchment (smooth relief) was chosen and by the use of correlation analysis and visual interpretation the following issues were studied, 1) Importance of topography on the spatial distribution of environmental variables based on topographic indices (Ln (Drainage area), tan ( angle slope) and topographic wetness index, TWI); 2) LPJ-GUESS ability to catch the environmental variables spatial distribution and 3) Implementation of a coupled LPJ-GUESS - topographic indices model to account for the topography influence on hydrology and assessment of its performance on modelling the spatial patterns of environmental variables.
Results of the first two topics showed how LPJ-GUESS could not catch the spatial variations of satellite based LAI, and that even the gentle topography of the catchment was an important issue on explaining the heterogeneity of vegetation related variables. Nevertheless, there are many factors, like climate conditions, which affect the strength of this relationship, as reflected on low correlation coefficients (never over 0.25), the variable correlation coefficients along the year and the identification of areas more related to the topographic indexes than others. Additionally, TWI was selected, based on its higher correlations with respect to the other topographic indices, to be one used to represent the topography influence in the catchment. The integrated model, LPJ-Topographic index (LPJ-TI), use the TWI to make a cell wise characterization and create weights affecting the water inputs to the soil layer as a way to account for hydrological processes driven by topography. LPJ-TI showed localized and time dependent improvement of the spatial representation of the satellite based LAI. These results confirm the need to include the topographic influence on the hydrological module of LPJ-GUESS and present a possible low computational method to start working on. (Less)
Popular Abstract
Ecosystem modelling is an always evolving science trying to catch the complexity of the nature and its principles to model the ecosystem in a realistic way. Over and over, models are being modified or complemented to make better predictions and achieve better representations of phenomena of interest like the responses of the ecosystem to a fast changing world (climate change, land use change). LPJ-GUESS is a flexible dynamic ecosystem model widely used to model vegetation, water and carbon cycles in terrestrial ecosystems. In order to model an ecosystem in LPJ-GUESS the area of interest is gridded in cells, where every cell is modelled independently; that is there is no communication between the cells so important interactions such as... (More)
Ecosystem modelling is an always evolving science trying to catch the complexity of the nature and its principles to model the ecosystem in a realistic way. Over and over, models are being modified or complemented to make better predictions and achieve better representations of phenomena of interest like the responses of the ecosystem to a fast changing world (climate change, land use change). LPJ-GUESS is a flexible dynamic ecosystem model widely used to model vegetation, water and carbon cycles in terrestrial ecosystems. In order to model an ecosystem in LPJ-GUESS the area of interest is gridded in cells, where every cell is modelled independently; that is there is no communication between the cells so important interactions such as water movement do not occur; dynamic particularly important at watershed levels.
Topography is an important driver on determining the flow of water on a catchment, thus influences de distribution of water over the area, process being evident on differential soil moisture, vegetation, vegetation growth, decomposition, etc. Topographic characteristic can be summarized on topographic indices, which aim to represent the key hydrological processes driven by topography in a simplified but realistic way. Some of the most used topographic indices related to the distribution of water over the landscape are: slope, drainage area and, a combination of former ones, the topographic wetness index.
Based on the former information, the current thesis considered important to assess the modelled LPJ-GUESS distribution of the environmental variables values over the area and to evaluate a method to include the effect of topography over the hydrology in the model. For this; Alergaarde catchment, a catchment with little relief located on central Jutland Denmark, was chosen, and by the use of correlation analysis and visual interpretation of the observed and simulated spatial patterns of environmental variables (soil moisture and vegetation development represented as Leaf area index - LAI) the following issues were studied: 1) Importance of topography on the spatial distribution of environmental variables based on topographic indices (Ln (Drainage area), tan ( angle slope) and topographic wetness index, TWI); 2) LPJ-GUESS ability to catch the environmental variables spatial distribution and 3) Implementation of a coupled LPJ-GUESS - topographic indices model ( LPJ-Topographic index, LPJ-TI) to account for the topography influence on hydrology and assessment of its performance on modelling the spatial patterns of environmental variables. The coupled model, LPJ-TI, bases on making a cell wise characterization of the catchment based on giving weights to the range of values of the topographic index and using them to affect the water going into the soil layer as a way to account for hydrological processes driven by topography.
Results and conclusions
The results of the first two topics showed how LPJ-GUESS could not catch the spatial variations of LAI, and that even the gentle topography of the catchment was an important issue on explaining the heterogeneity of vegetation related variables. Nevertheless, it was also noticed that there are many factors (ex. weather conditions, land management activities) affecting the strength of the relationship between topography and plant development (i.e. LAI), as reflected by the low correlation coefficients (never above 0.25), stronger and lower correlation depending on the month in consideration, and the identification of areas more related to the topographic indexes than others within the same time frame. Additionally on the first topic, TWI was proven to be a good index for demonstrating the association of topography with LAI and was therefore selected to be used on the model LPJ-TI.
Regarding the last issue, LPJ-TI showed localized and time dependent improvement of the spatial representation of LAI. These results confirm the need to include the topographic influence on the hydrological module of LPJ-GUESS and present a possible low computational method to start working on. (Less)
Please use this url to cite or link to this publication:
author
Narváez Vallejo, Alejandra LU
supervisor
organization
course
GISM01 20152
year
type
H2 - Master's Degree (Two Years)
subject
keywords
smooth topography, drainage area, slope, topographic wetness index, LPJ-GUESS, GIS, physical geography and ecosystem analysis, geography, geographic information systems, leaf area index, spatial patterns, MODIS LAI.
publication/series
Master Thesis in Geographical Information Science
report number
46
language
English
id
8598844
date added to LUP
2016-02-08 11:13:45
date last changed
2016-02-11 08:50:58
@misc{8598844,
  abstract     = {Ecosystem modelling is an always evolving science trying to catch the complexity of the nature and its principles to model environmental responses in a realistic way. Over and over, models try to introduce more variables and interactions to achieve better representations of phenomena of interest like the responses of the ecosystem to a fast changing world (climate change, land use change). LPJ-GUESS is a flexible dynamic ecosystem model widely used to model the structure and dynamics of terrestrial ecosystems. It is based on plant physiology, biochemical cycles and feedbacks on independent gridcells, there is no consideration of lateral transfer of water between cells. On the other hand, soil moisture is essential for vegetation growth and its distribution is known to be driven by the topography of the landscape, which drives the lateral transfer of water. Based on this, it was considered important to assess the modelled spatial representation of environmental variables (soil moisture, LAI) from LPJ-GUESS and to evaluate a possible method to include the effect of topography over the hydrology in LPJ-GUESS model. For this, Alergaarde catchment (smooth relief) was chosen and by the use of correlation analysis and visual interpretation the following issues were studied, 1) Importance of topography on the spatial distribution of environmental variables based on topographic indices (Ln (Drainage area), tan ( angle slope) and topographic wetness index, TWI); 2) LPJ-GUESS ability to catch the environmental variables spatial distribution and 3) Implementation of a coupled LPJ-GUESS - topographic indices model to account for the topography influence on hydrology and assessment of its performance on modelling the spatial patterns of environmental variables. 
Results of the first two topics showed how LPJ-GUESS could not catch the spatial variations of satellite based LAI, and that even the gentle topography of the catchment was an important issue on explaining the heterogeneity of vegetation related variables. Nevertheless, there are many factors, like climate conditions, which affect the strength of this relationship, as reflected on low correlation coefficients (never over 0.25), the variable correlation coefficients along the year and the identification of areas more related to the topographic indexes than others. Additionally, TWI was selected, based on its higher correlations with respect to the other topographic indices, to be one used to represent the topography influence in the catchment. The integrated model, LPJ-Topographic index (LPJ-TI), use the TWI to make a cell wise characterization and create weights affecting the water inputs to the soil layer as a way to account for hydrological processes driven by topography. LPJ-TI showed localized and time dependent improvement of the spatial representation of the satellite based LAI. These results confirm the need to include the topographic influence on the hydrological module of LPJ-GUESS and present a possible low computational method to start working on.},
  author       = {Narváez Vallejo, Alejandra},
  keyword      = {smooth topography,drainage area,slope,topographic wetness index,LPJ-GUESS,GIS,physical geography and ecosystem analysis,geography,geographic information systems,leaf area index,spatial patterns,MODIS LAI.},
  language     = {eng},
  note         = {Student Paper},
  series       = {Master Thesis in Geographical Information Science},
  title        = {Can the introduction of the topographic indices in LPJ-GUESS improve the spatial representation of environmental variables?},
  year         = {2016},
}