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Impact of vegetation responses to climate change on the hydrological system in Belgium.
On a global scale, increasing atmospheric CO2 concentrations ([CO2]) and the associated process of global warming cause climatic changes. They include increased air temperatures, altered rainfall patterns and a higher occurrence of extreme weather episodes. In Belgium, expected climaticchanges include higher temperatures year round, wetter winters and drier summers. Agricultural production and its available water resources arehighly vulnerable to climatic changes. The magnitude and direction of the climate change impact on agricultural production and the soil water balance depend on location and environment. Generally, elevated [CO2] benefit crop production by stimulating photosynthesis and simultaneously reducing crop transpiration (through stomatal closure). Decreases in rainfall can lead to water stress for crops and drier soils. But also floods and changes in rainfall intensity can be harmful for agricultural fields. Temperature increases lead to a higher evaporative demand of the atmosphere. If temperatures rise to supra-optimal temperatures, crop production is at risk. In temperate regions at mid latitude however, moderate rises in air temperature extend the length of the suitable growing period and allow to grow late maturing cultivars with a higher production potential. In this research, the impact of combined changes in weather variables and [CO2] on four important crops in the Flemish Region ofBelgium was assessed with process-based crop models, driven by future weather projections from climate models.
First, scenarios offuture local-scale weather were generated for the study area. Scenarioswere constructed by downscaling climate signals from two ensembles of global (GCMs, from the Coupled Model Intercomparison Project (CMIP3)) andregional climate models (RCMs, from the EU-ENSEMBLES project (ENS)) by the stochastic weather generator LARS-WG. All models used in this research projected temperature increases but the CMIP3-based scenarios were generally more pronounced than the ENS-based scenarios. For precipitation,projected trends in change were less univocal.
Next, the AquaCrop model was selected as impact model and prepared for the assessment study. AquaCrop is a functional, multi-crop model that is principallywater-driven and simulates crop development and production. At the coreof the model is the biomass production, which is simulated in exchange for water transpired by the developing crop canopy. The proportional factor between transpiration and biomass production is the water productivity parameter.
To augment the understanding of and adapt themodel for crop responses to elevated [CO2], a statistical meta-analysis of research results of free air CO2 enrichment (FACE) studies was performed. The most prominent analysis results were the positive correlation between [CO2] and biomass/yield production and the negative correlation between [CO2] and evapotranspiration. They lead to a substantial increase in water productivity for crops (for both C3 andC4type crops). Additionally, changes in root:shoot ratio and phenology were apparent. Based on the results of the meta-analysis, a correction factor was introduced in AquaCrop to correct transpiration downwards with increasing [CO2]. Additionally, a flexible response of the water productivity parameter to elevated [CO2] was introduced to capture the variation in crop responsiveness associated with crop sink strength. Limited sink strength of a crop in the field, e.g. as a result of sub-optimal nitrogen availability, can suppress the crop responsiveness to CO2. The research results suggest that considering crop sink strength and variationin responsiveness is equally relevant to considering climatic changes and elevated [CO2] when assessing future crop production. Indicativevalues for crop responsiveness (representing sink strength) were proposed for all crops currently available in the AquaCrop database.
Subsequently, a global sensitivity analysis of the AquaCrop model output to changes in model parameters was performed, and the model was calibrated and validated for the temperate maritime climate of Belgium. Thesensitivity analysis consisted of a Morris screening followed by an EFAST analysis. The analysis revealed important interaction effects betweenparameters and some irrelevant parameters, for which suggestions for model simplification were formulated. In general, the models yield outputsensitivity to important parameters depends strongly on environmental conditions but thematic categories of parameters that merit attention according to different local conditions can be distinguished.
The calibration and validation of the AquaCrop model was performed basedon field data collected on farmers fields. AquaCrop could be satisfactorily calibrated and validated for winter wheat (Triticum aestivum L.), maize (Zea mays L.), potato (Solanum tubersosum L.) and sugar beet (Beta vulgaris L.) in the actual temperate maritime climate of Belgium. Given the earlier successful validation of the model in warmer conditions, under more severe levels of water stress and at elevated [CO2], and given the models physiological base, it was assumed that AquaCrop can be used under the future climate conditions. Winter cereals form an exception because particularities characteristic to these winter crops, including dormancy, cold hardening and vernalization, are summarized in AquaCrop. Yet, it turned out that without explicit consideration of these processes, simulated crop development responds too strongly to the projected future temperatures increase. Thus, the wheat model Sirius, which explicitly considers these processes, was selected to perform winter wheat simulations under future climate conditions.
Finally, the impact assessment of climatic changes on the four major crops in the FlemishRegion was performed by using the climate projections as input for the impact models AquaCrop and Sirius. Even though impacts vary among crops,environment and projected climatic changes, there are clear trendsvisible. Advantages of climate change dominate over negative effects for meancrop production in Belgium towards the middle of this century. Elevated [CO2] benefits production of winter wheat, potato and sugar beet and counteracts potential negative effects of supra-optimal temperatures and precipitation changes. Maize benefits less from elevated [CO2] than the C3 crops and can suffer from drought stress under the projectedclimatic changes. Adaption of cultivation management (including shiftedsowing dates and late maturing cultivars) shows additionally potential to augment the mean production level of spring-sown crops. Yet, climaticchanges and adapted management also have an impact on interannual yieldstability, which decreases generally for spring-sown crops. Even thoughthe projected climatic changes may lead to mean production gains in theFlemish Region of Belgium, the soil water balance can be negatively affected. Often, this increases the incidence of drought stress for crops, which increases the crops vulnerability and affects the yield stabilitynegatively. Only for winter wheat, changes in climate affect much less the soil water balance and interannual yield stability.
This research does not pretend to represent the future reality. Instead, it provides probable future trends, which may be expected in agriculture in the coming decades under a changing climate. Uncertainty related to climate scenario generation propagates to the impact assessment. Although we canonly speculate that RCM-based scenarios may be more advanced than GCM-based scenarios for agricultural impact assessments, the research resultsdemonstrate definitely that the choice of one or another ensemble of climate models (with different resolution) adds to the overall uncertaintyof climate change impact assessments in agriculture.
First, scenarios offuture local-scale weather were generated for the study area. Scenarioswere constructed by downscaling climate signals from two ensembles of global (GCMs, from the Coupled Model Intercomparison Project (CMIP3)) andregional climate models (RCMs, from the EU-ENSEMBLES project (ENS)) by the stochastic weather generator LARS-WG. All models used in this research projected temperature increases but the CMIP3-based scenarios were generally more pronounced than the ENS-based scenarios. For precipitation,projected trends in change were less univocal.
Next, the AquaCrop model was selected as impact model and prepared for the assessment study. AquaCrop is a functional, multi-crop model that is principallywater-driven and simulates crop development and production. At the coreof the model is the biomass production, which is simulated in exchange for water transpired by the developing crop canopy. The proportional factor between transpiration and biomass production is the water productivity parameter.
To augment the understanding of and adapt themodel for crop responses to elevated [CO2], a statistical meta-analysis of research results of free air CO2 enrichment (FACE) studies was performed. The most prominent analysis results were the positive correlation between [CO2] and biomass/yield production and the negative correlation between [CO2] and evapotranspiration. They lead to a substantial increase in water productivity for crops (for both C3 andC4type crops). Additionally, changes in root:shoot ratio and phenology were apparent. Based on the results of the meta-analysis, a correction factor was introduced in AquaCrop to correct transpiration downwards with increasing [CO2]. Additionally, a flexible response of the water productivity parameter to elevated [CO2] was introduced to capture the variation in crop responsiveness associated with crop sink strength. Limited sink strength of a crop in the field, e.g. as a result of sub-optimal nitrogen availability, can suppress the crop responsiveness to CO2. The research results suggest that considering crop sink strength and variationin responsiveness is equally relevant to considering climatic changes and elevated [CO2] when assessing future crop production. Indicativevalues for crop responsiveness (representing sink strength) were proposed for all crops currently available in the AquaCrop database.
Subsequently, a global sensitivity analysis of the AquaCrop model output to changes in model parameters was performed, and the model was calibrated and validated for the temperate maritime climate of Belgium. Thesensitivity analysis consisted of a Morris screening followed by an EFAST analysis. The analysis revealed important interaction effects betweenparameters and some irrelevant parameters, for which suggestions for model simplification were formulated. In general, the models yield outputsensitivity to important parameters depends strongly on environmental conditions but thematic categories of parameters that merit attention according to different local conditions can be distinguished.
The calibration and validation of the AquaCrop model was performed basedon field data collected on farmers fields. AquaCrop could be satisfactorily calibrated and validated for winter wheat (Triticum aestivum L.), maize (Zea mays L.), potato (Solanum tubersosum L.) and sugar beet (Beta vulgaris L.) in the actual temperate maritime climate of Belgium. Given the earlier successful validation of the model in warmer conditions, under more severe levels of water stress and at elevated [CO2], and given the models physiological base, it was assumed that AquaCrop can be used under the future climate conditions. Winter cereals form an exception because particularities characteristic to these winter crops, including dormancy, cold hardening and vernalization, are summarized in AquaCrop. Yet, it turned out that without explicit consideration of these processes, simulated crop development responds too strongly to the projected future temperatures increase. Thus, the wheat model Sirius, which explicitly considers these processes, was selected to perform winter wheat simulations under future climate conditions.
Finally, the impact assessment of climatic changes on the four major crops in the FlemishRegion was performed by using the climate projections as input for the impact models AquaCrop and Sirius. Even though impacts vary among crops,environment and projected climatic changes, there are clear trendsvisible. Advantages of climate change dominate over negative effects for meancrop production in Belgium towards the middle of this century. Elevated [CO2] benefits production of winter wheat, potato and sugar beet and counteracts potential negative effects of supra-optimal temperatures and precipitation changes. Maize benefits less from elevated [CO2] than the C3 crops and can suffer from drought stress under the projectedclimatic changes. Adaption of cultivation management (including shiftedsowing dates and late maturing cultivars) shows additionally potential to augment the mean production level of spring-sown crops. Yet, climaticchanges and adapted management also have an impact on interannual yieldstability, which decreases generally for spring-sown crops. Even thoughthe projected climatic changes may lead to mean production gains in theFlemish Region of Belgium, the soil water balance can be negatively affected. Often, this increases the incidence of drought stress for crops, which increases the crops vulnerability and affects the yield stabilitynegatively. Only for winter wheat, changes in climate affect much less the soil water balance and interannual yield stability.
This research does not pretend to represent the future reality. Instead, it provides probable future trends, which may be expected in agriculture in the coming decades under a changing climate. Uncertainty related to climate scenario generation propagates to the impact assessment. Although we canonly speculate that RCM-based scenarios may be more advanced than GCM-based scenarios for agricultural impact assessments, the research resultsdemonstrate definitely that the choice of one or another ensemble of climate models (with different resolution) adds to the overall uncertaintyof climate change impact assessments in agriculture.
Date:1 Oct 2008 → 15 Oct 2014
Keywords:Hydrological modelling, Grote Nete, Climate change, Crop development, MIKE-SHE, Dynamic model, AquaCrop, Soil water balance
Disciplines:Soil sciences, challenges and pollution, Agriculture, land and farm management, Physical geography and environmental geoscience, Construction engineering, Earthquake engineering, Geotechnical and environmental engineering, Water engineering, Wind engineering
Project type:PhD project