Quantifying the Impact of Climate Change and Extreme Heat on Rice in the United States

The United States (U.S.) is the world 's 4th largest rice exporter and challenges associated with extreme heat and water availability may pose a threat to future productivity. Forecasts from multiple CMIP6 climate models were linked with geospatial data and a version of the ORYZA crop model, revised with updates to phenology, heat stress, gas exchange, and energy balance components, to evaluate yield and water use efficiency (WUE) in response to future climate projections using four region specific heat tolerant versus sensitive rice cultivars. Rising temperatures were projected to reduce yield by 12 -25 % and 22 -41 % for the 2040s and 2070s, respectively. California and the north Mississippi Delta were the most vulnerable regions. Elevated atmospheric CO 2 was projected to compensate for 18 -42 % of yield losses in the 2070s and could alleviate most negative impacts of rising temperatures on heat-tolerant crop varieties. Heat-sensitive cultivars still experienced 1 to 5 % yield reductions during the same periods. The cultivar distinction was particularly evident in 2070s under SSP585 scenario, in which yields for the heat tolerant cultivars were 12 % greater than heat sensitive ones. A significant portion of predicted yield loss was attributed to reduced spikelet fertility due to heat stress during anthesis. Thus, breeding for heat tolerance and high-yield traits is a potential strategy for climate adaptation. Without elevated CO 2 , WUE is likely to decline by 14 -25 % for 2040, and 23 -42 % for the 2070s. These WUE reductions were mitigated-3 % to 7 % and-4 % to 8 % for the 2040s and 2070s under elevated CO 2 . This modelbased effort provides unique spatial assessments regarding projected climate impacts on potential rice yield and water use and highlights the need for integrating crop genetic and region-specific adaptation strategies to maintain sustainable rice production.