Leaf- to field-level compound effects of warm and dry conditions on crops and potential mitigating strategies

Abstract: Ongoing climate change has been threatening global food security. Under climate change, increasing risk of hot and dry conditions (termed compound events) is projected in many agricultural regions. Compound events cause detrimental effects on crops, yet their effects have rarely been quantified based on modeling approach. In this thesis, we established mechanistic and statistical models to analyze crop canopy temperature, transpiration rate, and yield responses to compound effects. We aimed to explore the compound effects on crops and help identifying adaptation strategies. Our results suggested that hot and dry conditions interacted in enhancing canopy temperature, i.e. the risk of potential crop heat stress, and crop yield losses. Both canopy temperature and yield losses increased from wet-cool conditions to dryhot conditions. Short-term intra-seasonal conditions and growing season averages were equally important in assessing crop responses to compound events. More intermittent precipitation regimes and longer dry spells negatively affected canopy temperature and yields even when the mean climatic conditions remained unaltered. Rainfed crop yields showed yield maximizing precipitation, which increased with temperature. As one of the adaptation strategies, irrigation could alleviate but not cancel the negative effects of adverse climate. Another adaptation is a shift from annual to perennial grain crops. Whether perennial grain crops are less vulnerable to heat and water stress depends on some key plant traits, such as leaf area index, which should be targeted for future breeding program to adapt to climate change.