Title: Crop Responses to Climate Change: Impact on Agricultural Production and the Soil Water Balance in the Flemish Region of Belgium
Other Titles: Gewasrespons op klimaatverandering: Impact voor landbouwproductie en bodemwaterbalans in Vlaanderen, België
Authors: Vanuytrecht, Eline
Issue Date: 15-Oct-2013
Abstract: 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 climatic changes include higher temperatures year round, wetter winters and drier summers. Agricultural production and its available water resources are highly 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 of Belgium was assessed with process-based crop models, driven by future weather projections from climate models. First, scenarios of future local-scale weather were generated for the study area. Scenarios were constructed by downscaling climate signals from two ensembles of global (GCMs, from the Coupled Model Intercomparison Project (CMIP3)) and regional 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 principally water-driven and simulates crop development and production. At the core of 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 the model 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 variation in responsiveness is equally relevant to considering climatic changes and elevated [CO2] when assessing future crop production. Indicative values 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. The sensitivity analysis consisted of a Morris screening followed by an EFAST analysis. The analysis revealed important interaction effects between parameters and some irrelevant parameters, for which suggestions for model simplification were formulated. In general, the model’s yield output sensitivity 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 based on 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 model’s 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 Flemish Region 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 mean crop 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 projected climatic changes. Adaption of cultivation management (including shifted sowing dates and late maturing cultivars) shows additionally potential to augment the mean production level of spring-sown crops. Yet, climatic changes and adapted management also have an impact on interannual yield stability, which decreases generally for spring-sown crops. Even though the projected climatic changes may lead to mean production gains in the Flemish Region of Belgium, the soil water balance can be negatively affected. Often, this increases the incidence of drought stress for crops, which increases the crop’s vulnerability and affects the yield stability negatively. 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 can only speculate that RCM-based scenarios may be more advanced than GCM-based scenarios for agricultural impact assessments, the research results demonstrate definitely that the choice of one or another ensemble of climate models (with different resolution) adds to the overall uncertainty of climate change impact assessments in agriculture.
Table of Contents: Problem statement and research questions
Chapter 1 Climate scenarios
Chapter 2 Crop responses to CO2
Chapter 3 The AquaCrop model
Chapter 4 Modelling the responses to CO2 with AquaCrop
Chapter 5 Global sensitivity analysis of AquaCrop
Chapter 6 Calibration of AquaCrop in the temperate maritime climate of Belgium
Chapter 7 Impact on crop production and the soil water balance
Conclusions and perspectives
ISBN: 978-90-8826-319-4
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Division Soil and Water Management
Hydraulics Section
Department of Civil Engineering - miscellaneous

Files in This Item:
File Status SizeFormat
Dissertation_EVanuytrecht.pdf Published 7715KbAdobe PDFView/Open Request a copy

These files are only available to some KU Leuven Association staff members


All items in Lirias are protected by copyright, with all rights reserved.