The here and now of climate change: Climatic trends throughout Australian cotton regions and implications for the growing season

Context: Much research has focused on assessing future climatic conditions on cotton production. However, understanding climatic changes that have already occurred throughout Australian cotton regions may provide insights on how existing and new regions are adapting to change. Objectives: This study aims to understand climatic changes that have occurred throughout Australian cotton regions, and the implications that these changes may have had for cotton growth and development. Methods: We utilised historical weather data to undertake an analysis of regional climate using changes in: heat unit accumulation for seasonal assessment of temperature conditions; frequency of extreme weather conditions affecting cotton growth; seasonal potential evapotranspiration (ETO); and the timing of key cotton developmental stages. Nine Australian cotton regions over three time periods from 1961 to 2020 were assessed. We also used the cotton simulation model OZCOT to predict yield, crop evapotranspiration (ETC), and water use efficiency (WUE, lint yield kg/mm ETC) for a crop grown at each location. Results: Our data shows some reductions in early season cold shocks ( <= 11 degrees C min.), and increases in minimum temperature, seasonal heat accumulation, ETO, and the frequency of extremely high temperatures ( >40 degrees C). Overall, time to first flower (FF) has decreased across several locations which may be having implications for less leaf area prior to flowering, but it may be contributing to an opportunity for longer reproductive periods at Emerald and Moree. Conclusions: Climatic changes including decreased frequency of early season cold shocks, increased minimum temperatures and frequency of high temperatures and evapotranspiration, and an increase in season long heat accumulation have occurred across Australian cotton regions from 1961 to 2020, affecting growth and development of cotton. Overall, warmer seasonal temperatures have reduced the time to first flower, increased the time to last effective flower (LEF), and resulted in some changes to last harvestable boll (LHB). Implications: Climatic changes have resulted in an opportunity for longer reproductive periods and the potential for increased yields. Recognising that regions have experienced specific changes may help to guide current and future agronomic practice in the different regions.