Crop evapotranspirative cooling across spatio-temporal scales

Plants experience heat stress when exposed to high temperatures. High temperature events have caused shocks to food production in some of the world's most important growing regions, and global heating is expected to increase the frequency and magnitude of such events. Evapotranspirative cooling is a mechanism of heat avoidance at plant, farm and regional scale. In this thesis, the importance of evapotranspirative cooling is explored at all three of these scales. At the plant scale, thousands of observations of leaf temperature are used to explore the magnitude of heat avoidance from transpirational cooling and its connection to heat tolerance. At the farm scale, the ORYZA crop model is used to test the importance of transpirational cooling in modelling the trade-off between saving water and heat avoidance in irrigated rice. At the regional scale, large spatial data sets of irrigated rice area are used in combination with observed temperature data to examine the impact of landscape wide irrigation on heatwaves in India over the historical period. The results of this thesis show that evapotranspirative cooling is an important heat avoidance mechanism in common bean. The first empirical evidence demonstrating a connection between transpirational cooling and heat tolerance in common bean is presented. At the farm scale, evapotranspirative cooling is shown to explain a far greater share of variability in yield than changes in irrigation strategy. Modelling of evapotranspirative cooling is shown to be a key uncertainty in efforts to understand the trade-off between saving water and resilience to heat stress in a warming climate. Finally, region-wide irrigation is shown to reduce the frequency and duration of heatwaves in India.