Publication
Efficient tools to simulate main crops in Portugal for decision support systems
| Summary: | Agricultural systems are inherently vulnerable to climate variability and climate change is expected to increase this vulnerability. Various studies warn the anthropogenic-driven global warming with elevated CO2 concentration and altered regional precipitation pattern, are expected to negatively affect local crop productivity and thus exacerbate food insecurities in many regions worldwide, particularly for Mediterranean basin. Mediterranean basin is one of the most prominent climate change “hotspot” due to ongoing and projected changes in both climate means and variabilities, comprising a robust climate change signal of an overall warming and drying trend, accompanied by more frequent occurrence of severe drought and extreme high temperatures. Specifically, these projected changes are expected to be more pronounced in southern Europe, such as in Portugal, where annual mean temperature has increased at a rate more than double the global warming rate in the past decades, along with the observed decreases in precipitation and its enhanced inter-annual variability. Therefore, it is urgently needed to carry out the assessment of climate change impacts on agricultural production and explore suitable adaptation strategies, whereas the related studies so far remain scarce in Portugal. We had chosen three important cropping systems for Portuguese agriculture, i.e. irrigated maize, rainfed wheat and perennial forage grassland, while representative study sites in their current principal growing regions were identified accordingly. The overall methodology follows combined use of climate and crop models, where the spatially-downscaled bias-corrected climate change projections from climate models were utilized to drive crop model simulations at study sites, which were prior calibrated using local observed weather, soil and management data. For employed process-based crop models, both STICS and AquaCrop were applied for the irrigated maize production, whereas the other two cropping systems were only analyzed using STICS model. It was noteworthy one major strength from current studies consisted in, on top of projected mean climate changes, we had consistently incorporated the effects of potential changes in climate variability and its associated extreme weather events into the simulated impacts (e.g. yield changes) for a more reliable assessment. The results indicate threats and risks of future climate change are substantially high for agriculture production in Portugal. Because an overall negative climate change impact from the mid until the end of 21st century is obtained for all three important cropping systems, corresponding to moderate-to-severe yield losses with increased inter-annual variabilities. Yield losses are greater in magnitude with higher year-to-year variability, in the second half of the century than in the first half, and in a high emission pathway than in a low emission scenario. The CO2 fertilization effect is unlikely to compensate these yield reductions, where it brings more yield increment for C3 species (wheat and defined grass mixture) than for C4 (maize). Specifically, majority of negative impacts are derived from the shortened growth duration for irrigated maize under a warmer climate, and from intensified drought and heat stresses during a sensitive period (grain-filling) for rainfed wheat or during an unfavorable summer period for perennial grassland. These aspects correspond to the vulnerabilities of cropping systems facing climate change. It is interesting to note though higher temperature is clearly detrimental to irrigated maize production, it facilitates advanced phenology of perennial grass shifting towards the favorable cool and wet winter period for enhanced production or it may also help rainfed wheat crop to mature earlier to avoid excessive terminal stresses. Yet the magnitude of climate change impacts on agricultural productivity remains uncertain, varying with analyzed cropping systems, locations and management practices, applied climate models (including downscaling approaches) and crop models (including partial or full calibration), selected time periods and emission pathways. Adaptation strategies provide potential to mitigate these negative impacts, and development of appropriate and risk-focused adaptation policy should address previously identified vulnerabilities and prioritize available options for an integrated and comprehensive strategy. For annual cereal crops, increased irrigation amount at various levels has been firstly tested for irrigated maize cropping system under climate change, taking into account crop water demand and projected seasonal rainfall distribution. Though increased irrigation is able to mitigate yield reductions and maintain current yield levels, crop WUE considerably declines as a result of diminished yield responsiveness to seasonal water input with shorter growth duration. In view of increasing risks of water scarcity and decreasing portion of fresh water available for agriculture in the Mediterranean basin, solely increased irrigation supply might not be a feasible strategy, whereas the adaptive response for maize should be prioritized to promote water-saving techniques and maximize WUE for stabilizing yields (marginal reductions allowed). Combining optimized irrigation strategy (e.g. deficit irrigation) and installed efficient facilities (e.g. drip irrigation system) with other adaptation options, including introducing longer cycle cultivars and advanced sowing dates to counterbalance the shortened growing duration, is recommend, but should be further rigorously examined. For the rainfed wheat cropping system, adaptation priority should address the exacerbated risks of drought and heat stresses during the sensitive anthesis and grain-filling periods. The terminal stress escaping strategy is proposed by firstly testing early flowering cultivars (also known as short-cycle genotypes), where the trade-off between lower risk of exposure to terminal stress and higher risk of reduced yield potential tends to be positive, leading to net yield gains. Still, this option needs to be combined with other adaptation opportunities including early sowing date, wheat cultivars with less or no vernalization requirement (e.g. using spring wheat) and supplementary irrigation during the sensitive stage. Early sowing is expected to achieve the same stress escaping goals by anticipation of growth cycle. But winter warming during early sowing window could potentially slow vernalization fulfillment, with limited benefits to advance the susceptible stages. Using earlyflowering spring wheat cultivars (the earliness threshold must be carefully defined) thus can help advocating early sowing practice that potentially make use of more autumn-winter rainfall. Nevertheless, the proposed stress escaping strategy is found to be comparatively more useful to avoid enhanced terminal heat stress (>38º last over a short period) than prolonged terminal drought stress, where the latter can be alleviated with optimized supplemental irrigation. Adaptation strategy for perennial forage grassland should take advantage of opportunity and tackle the challenge, both arising from climate change. Benefiting from advanced phenology towards winter and early spring with alleviated cold stress and enriched ambient CO2 concentration, adaptation measures should focus on maximizing growth potential during this favorable period. These include optimized resource use (balanced early fertilization strategy with limited N leaching) and using grass-legume mixture for flexible forage utilization and better exploiting the stimulated CO2 responsiveness. In contrast, to cope with the challenge of exacerbated risks of summer heat and drought stresses, future breeding programs should ensure a diversification (intra- and interspecific variations) of available germplasms in phenology (fit new seasonal climate pattern), heat tolerance and dehydration tolerance for principal forage species. Specifically, continuous improvement of drought persistence and summer dormancy traits should gain more importance for rainfed Mediterranean grassland. Moreover, these drought survival traits should be integrated into plant materials with deeper root system to enhance water uptake (e.g. more of tall fescue), but it may raise forage quality issues that remain unassessed. Besides, we also hypothesize it is possible to adapt to summer drought from a management perspective without the needs to improve and diversify the species and variety mixture. The findings suggest that provided minimum soil moisture is guaranteed by supplemental irrigation to ensure adequate drought survival rate and standing density, breeding efforts should be more motivated towards heat tolerance, particularly in southern Portugal. Meanwhile, this measure is likely to result in a considerable increase in irrigation need, rendering a similar water-restriction issue facing irrigated maize. Crop yield projections and explored adaptation strategies are essential to assess the regional food security prospects and provide crucial information to support planning and implementing suitable adaptation strategies for farmers and policymakers in Portugal and in Mediterranean basin that is known to be susceptible to climate change. Despite the uncertainties in the magnitude of yield impacts and quantitative effectiveness of adaptations, the proposed and recommended adaptation strategies can represent promising opportunities to maintain or increase production in future climate while minimize environment impacts. Future research efforts should be directed towards using multi-model ensembles (both crop and climate models) to quantify the uncertainties and make the estimations more robust and reliable, but sustained and extensive international cooperation is required. Moreover, stronger link of field experimentation with crop modelling is essential for a more mechanistic understanding of crop response to climate change, as well as the integration of crop model into economic modelling for complex farm-level assessment. These shall all contribute to appropriate manage the climate risks and comprehensively improve the resilience of cropping system |
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| Main Authors: | Chenyao Yang |
| Subject: | Cropping systems Crop modelling |
| Year: | 2019 |
| Country: | Portugal |
| Document type: | doctoral thesis |
| Access type: | open access |
| Associated institution: | Universidade de Trás-os-Montes e Alto Douro |
| Language: | English |
| Origin: | Repositório da UTAD |
| Summary: | Agricultural systems are inherently vulnerable to climate variability and climate change is expected to increase this vulnerability. Various studies warn the anthropogenic-driven global warming with elevated CO2 concentration and altered regional precipitation pattern, are expected to negatively affect local crop productivity and thus exacerbate food insecurities in many regions worldwide, particularly for Mediterranean basin. Mediterranean basin is one of the most prominent climate change “hotspot” due to ongoing and projected changes in both climate means and variabilities, comprising a robust climate change signal of an overall warming and drying trend, accompanied by more frequent occurrence of severe drought and extreme high temperatures. Specifically, these projected changes are expected to be more pronounced in southern Europe, such as in Portugal, where annual mean temperature has increased at a rate more than double the global warming rate in the past decades, along with the observed decreases in precipitation and its enhanced inter-annual variability. Therefore, it is urgently needed to carry out the assessment of climate change impacts on agricultural production and explore suitable adaptation strategies, whereas the related studies so far remain scarce in Portugal. We had chosen three important cropping systems for Portuguese agriculture, i.e. irrigated maize, rainfed wheat and perennial forage grassland, while representative study sites in their current principal growing regions were identified accordingly. The overall methodology follows combined use of climate and crop models, where the spatially-downscaled bias-corrected climate change projections from climate models were utilized to drive crop model simulations at study sites, which were prior calibrated using local observed weather, soil and management data. For employed process-based crop models, both STICS and AquaCrop were applied for the irrigated maize production, whereas the other two cropping systems were only analyzed using STICS model. It was noteworthy one major strength from current studies consisted in, on top of projected mean climate changes, we had consistently incorporated the effects of potential changes in climate variability and its associated extreme weather events into the simulated impacts (e.g. yield changes) for a more reliable assessment. The results indicate threats and risks of future climate change are substantially high for agriculture production in Portugal. Because an overall negative climate change impact from the mid until the end of 21st century is obtained for all three important cropping systems, corresponding to moderate-to-severe yield losses with increased inter-annual variabilities. Yield losses are greater in magnitude with higher year-to-year variability, in the second half of the century than in the first half, and in a high emission pathway than in a low emission scenario. The CO2 fertilization effect is unlikely to compensate these yield reductions, where it brings more yield increment for C3 species (wheat and defined grass mixture) than for C4 (maize). Specifically, majority of negative impacts are derived from the shortened growth duration for irrigated maize under a warmer climate, and from intensified drought and heat stresses during a sensitive period (grain-filling) for rainfed wheat or during an unfavorable summer period for perennial grassland. These aspects correspond to the vulnerabilities of cropping systems facing climate change. It is interesting to note though higher temperature is clearly detrimental to irrigated maize production, it facilitates advanced phenology of perennial grass shifting towards the favorable cool and wet winter period for enhanced production or it may also help rainfed wheat crop to mature earlier to avoid excessive terminal stresses. Yet the magnitude of climate change impacts on agricultural productivity remains uncertain, varying with analyzed cropping systems, locations and management practices, applied climate models (including downscaling approaches) and crop models (including partial or full calibration), selected time periods and emission pathways. Adaptation strategies provide potential to mitigate these negative impacts, and development of appropriate and risk-focused adaptation policy should address previously identified vulnerabilities and prioritize available options for an integrated and comprehensive strategy. For annual cereal crops, increased irrigation amount at various levels has been firstly tested for irrigated maize cropping system under climate change, taking into account crop water demand and projected seasonal rainfall distribution. Though increased irrigation is able to mitigate yield reductions and maintain current yield levels, crop WUE considerably declines as a result of diminished yield responsiveness to seasonal water input with shorter growth duration. In view of increasing risks of water scarcity and decreasing portion of fresh water available for agriculture in the Mediterranean basin, solely increased irrigation supply might not be a feasible strategy, whereas the adaptive response for maize should be prioritized to promote water-saving techniques and maximize WUE for stabilizing yields (marginal reductions allowed). Combining optimized irrigation strategy (e.g. deficit irrigation) and installed efficient facilities (e.g. drip irrigation system) with other adaptation options, including introducing longer cycle cultivars and advanced sowing dates to counterbalance the shortened growing duration, is recommend, but should be further rigorously examined. For the rainfed wheat cropping system, adaptation priority should address the exacerbated risks of drought and heat stresses during the sensitive anthesis and grain-filling periods. The terminal stress escaping strategy is proposed by firstly testing early flowering cultivars (also known as short-cycle genotypes), where the trade-off between lower risk of exposure to terminal stress and higher risk of reduced yield potential tends to be positive, leading to net yield gains. Still, this option needs to be combined with other adaptation opportunities including early sowing date, wheat cultivars with less or no vernalization requirement (e.g. using spring wheat) and supplementary irrigation during the sensitive stage. Early sowing is expected to achieve the same stress escaping goals by anticipation of growth cycle. But winter warming during early sowing window could potentially slow vernalization fulfillment, with limited benefits to advance the susceptible stages. Using earlyflowering spring wheat cultivars (the earliness threshold must be carefully defined) thus can help advocating early sowing practice that potentially make use of more autumn-winter rainfall. Nevertheless, the proposed stress escaping strategy is found to be comparatively more useful to avoid enhanced terminal heat stress (>38º last over a short period) than prolonged terminal drought stress, where the latter can be alleviated with optimized supplemental irrigation. Adaptation strategy for perennial forage grassland should take advantage of opportunity and tackle the challenge, both arising from climate change. Benefiting from advanced phenology towards winter and early spring with alleviated cold stress and enriched ambient CO2 concentration, adaptation measures should focus on maximizing growth potential during this favorable period. These include optimized resource use (balanced early fertilization strategy with limited N leaching) and using grass-legume mixture for flexible forage utilization and better exploiting the stimulated CO2 responsiveness. In contrast, to cope with the challenge of exacerbated risks of summer heat and drought stresses, future breeding programs should ensure a diversification (intra- and interspecific variations) of available germplasms in phenology (fit new seasonal climate pattern), heat tolerance and dehydration tolerance for principal forage species. Specifically, continuous improvement of drought persistence and summer dormancy traits should gain more importance for rainfed Mediterranean grassland. Moreover, these drought survival traits should be integrated into plant materials with deeper root system to enhance water uptake (e.g. more of tall fescue), but it may raise forage quality issues that remain unassessed. Besides, we also hypothesize it is possible to adapt to summer drought from a management perspective without the needs to improve and diversify the species and variety mixture. The findings suggest that provided minimum soil moisture is guaranteed by supplemental irrigation to ensure adequate drought survival rate and standing density, breeding efforts should be more motivated towards heat tolerance, particularly in southern Portugal. Meanwhile, this measure is likely to result in a considerable increase in irrigation need, rendering a similar water-restriction issue facing irrigated maize. Crop yield projections and explored adaptation strategies are essential to assess the regional food security prospects and provide crucial information to support planning and implementing suitable adaptation strategies for farmers and policymakers in Portugal and in Mediterranean basin that is known to be susceptible to climate change. Despite the uncertainties in the magnitude of yield impacts and quantitative effectiveness of adaptations, the proposed and recommended adaptation strategies can represent promising opportunities to maintain or increase production in future climate while minimize environment impacts. Future research efforts should be directed towards using multi-model ensembles (both crop and climate models) to quantify the uncertainties and make the estimations more robust and reliable, but sustained and extensive international cooperation is required. Moreover, stronger link of field experimentation with crop modelling is essential for a more mechanistic understanding of crop response to climate change, as well as the integration of crop model into economic modelling for complex farm-level assessment. These shall all contribute to appropriate manage the climate risks and comprehensively improve the resilience of cropping system |
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