Modelling impacts of climate and weather extremes on wheat cropping systems across New South Wales

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Australian wheat production is crucial to global food security, as Australia is one of the world’s major grain exporters. The NSW wheat belt is a main wheat production area in south-eastern Australia. Interannual wheat yields in the NSW wheat belt are highly variable, as the rainfed wheat cropping systems are significantly affected by recurrent climate and weather extremes. Ongoing climate change is projected to induce more extremes events, thereby leading to more unfavourable climate conditions for wheat production. This thesis aims to quantify the impacts of various climate and weather extremes on wheat yield in the present and explore their potential impacts in the future, thereby enhancing the capability of stakeholders to reduce yield losses. Five inter-related studies based on statistical regression-based models, process-based crop models, or the integration of both models were conducted in the NSW wheatbelt. Consistent findings demonstrate that: (1) Inter-annual variability of rainfall in winter and spring was largely responsible for wheat yield variation. (2) Seasonal agricultural drought conditions could be well monitored for the wheat belt using remote sensing information and machine learning-based statistical models. (3) APSIM simulated biomass, multiple climate extremes indices, NDVI, and SPEI were incorporated into the RF model to develop a hybrid model for improved modelling of impacts of climate extremes. Drought events throughout the growing season were identified as the main factor causing yield losses. (4) The wheat belt was expected to experience drier conditions in spring and winter but had little change in summer and autumn. By the end of the 21st century, over half of the wheat belt was at a high risk of experiencing spring and winter drought. (5) The hybrid model was used to assess the impacts of future climate and weather extremes on wheat yield. Increasing drought and heat events around reproductive stages were identified to be major threats causing yield losses in the future. This project enhanced systematic understanding of impacts of present and future climate and weather extremes on wheat yield and their likely changes in the future. However, certain aspects such as new crop cultivars, efficient management practices, pests and weed, were not explicitly considered in the modelling methods. Therefore, these findings should be further reconfirmed by models involving more influential information to guide agricultural production.
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