Evaluation of the LPJ-GUESS crop model under ambient and elevated CO2 concentrations.
(2022) In Student thesis series INES NGEK01 20221Dept of Physical Geography and Ecosystem Science
- Abstract
- In the future atmospheric CO2 concentrations might exceed 550 ppm according to the RCP8.5 scenario by mid-century from our current 410 ppm, while our world population is projected to surpass the 9.7 billion threshold within the same time span. This challenge leads to the raising of questions addressing future food security.
Elevated CO2 has been shown to not only increase photosynthetic rates in plants, but also to reduce stomatal conductance where both processes generate increases in biomass and yield. In this thesis, the performance of the LPJ-GUESS crop model in simulating observed wheat yields under both ambient and elevated CO2 concentrations has been evaluated. Observational data has been obtained from three free-air carbon... (More) - In the future atmospheric CO2 concentrations might exceed 550 ppm according to the RCP8.5 scenario by mid-century from our current 410 ppm, while our world population is projected to surpass the 9.7 billion threshold within the same time span. This challenge leads to the raising of questions addressing future food security.
Elevated CO2 has been shown to not only increase photosynthetic rates in plants, but also to reduce stomatal conductance where both processes generate increases in biomass and yield. In this thesis, the performance of the LPJ-GUESS crop model in simulating observed wheat yields under both ambient and elevated CO2 concentrations has been evaluated. Observational data has been obtained from three free-air carbon dioxide enrichment (FACE) facilities, located in Germany, the United States of America and Australia. Model benchmarking revealed issues regarding yield underestimation which were consistent for both ambient and elevated CO2 model runs. Nonetheless, the model managed to capture the CO2 response reasonably well. The simulated yields for the German site provided the best agreement between modelled and observed data, with a CO2 response of 12% compared to the 15% in field, when CO2 concentrations were increased by 180 ppm. Conversely, the American site led to the lowest agreement, due to strongly underestimated yields and a CO2 response of 33% (instead of 15%) that led to an average modelled yield increase of 2 t/ha once exposed to elevated CO2.
Furthermore, modelled leaf area index (LAI) development is consistently delayed by about 1.5 months for all locations. Water stress has been found to primarily affect wheat towards the end of the growing season in Australia, while some influence could be observed in the US as well. After exposure to elevated CO2, improvements in water stress levels could be noted. A comparison between field measurements of gross primary productivity (GPP), revealed that GPP is underestimated by 37%, while simulated net primary production (NPP) fluxes are overestimated by 25% in LPJ-GUESS. An offset of NPP in the beginning of the growing season leads to most of the NPP and biomass accumulating in a shorter time window towards the end of the growing period.
To be able to utilise this model for future crop grain estimates, issue regarding the underestimating yields and delayed LAI need to be solved first. Otherwise, it will become challenging to successfully project yields for future climate scenarios, where elevated CO2, increased temperature, and drought might interact simultaneously at the end of the growing period. As this is the period, where most of the biomass is accumulating, even lower yield estimates can be expected. In the future advances and improvements in crop growth models will become more important, which depend on availably of field data of high quality for purposes such as model validation and calibration, stressing the responsibility of experimentalists to include as many relevant measurements as possible. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9090196
- author
- Nitschke, Annika LU
- supervisor
-
- Thomas Pugh LU
- organization
- course
- NGEK01 20221
- year
- 2022
- type
- M2 - Bachelor Degree
- subject
- keywords
- LPJ-GUESS, free-air carbon dioxide enrichment experiments, elevated CO2, climate change, wheat yield
- publication/series
- Student thesis series INES
- report number
- 567
- language
- English
- id
- 9090196
- date added to LUP
- 2022-06-17 13:19:34
- date last changed
- 2022-06-17 13:19:34
@misc{9090196,
abstract = {{In the future atmospheric CO2 concentrations might exceed 550 ppm according to the RCP8.5 scenario by mid-century from our current 410 ppm, while our world population is projected to surpass the 9.7 billion threshold within the same time span. This challenge leads to the raising of questions addressing future food security.
Elevated CO2 has been shown to not only increase photosynthetic rates in plants, but also to reduce stomatal conductance where both processes generate increases in biomass and yield. In this thesis, the performance of the LPJ-GUESS crop model in simulating observed wheat yields under both ambient and elevated CO2 concentrations has been evaluated. Observational data has been obtained from three free-air carbon dioxide enrichment (FACE) facilities, located in Germany, the United States of America and Australia. Model benchmarking revealed issues regarding yield underestimation which were consistent for both ambient and elevated CO2 model runs. Nonetheless, the model managed to capture the CO2 response reasonably well. The simulated yields for the German site provided the best agreement between modelled and observed data, with a CO2 response of 12% compared to the 15% in field, when CO2 concentrations were increased by 180 ppm. Conversely, the American site led to the lowest agreement, due to strongly underestimated yields and a CO2 response of 33% (instead of 15%) that led to an average modelled yield increase of 2 t/ha once exposed to elevated CO2.
Furthermore, modelled leaf area index (LAI) development is consistently delayed by about 1.5 months for all locations. Water stress has been found to primarily affect wheat towards the end of the growing season in Australia, while some influence could be observed in the US as well. After exposure to elevated CO2, improvements in water stress levels could be noted. A comparison between field measurements of gross primary productivity (GPP), revealed that GPP is underestimated by 37%, while simulated net primary production (NPP) fluxes are overestimated by 25% in LPJ-GUESS. An offset of NPP in the beginning of the growing season leads to most of the NPP and biomass accumulating in a shorter time window towards the end of the growing period.
To be able to utilise this model for future crop grain estimates, issue regarding the underestimating yields and delayed LAI need to be solved first. Otherwise, it will become challenging to successfully project yields for future climate scenarios, where elevated CO2, increased temperature, and drought might interact simultaneously at the end of the growing period. As this is the period, where most of the biomass is accumulating, even lower yield estimates can be expected. In the future advances and improvements in crop growth models will become more important, which depend on availably of field data of high quality for purposes such as model validation and calibration, stressing the responsibility of experimentalists to include as many relevant measurements as possible.}},
author = {{Nitschke, Annika}},
language = {{eng}},
note = {{Student Paper}},
series = {{Student thesis series INES}},
title = {{Evaluation of the LPJ-GUESS crop model under ambient and elevated CO2 concentrations.}},
year = {{2022}},
}