Agricultural Irrigation Exacerbates Humid Heat Stress in the Mid-Lower Reaches of the Yangtze River

Massive irrigation across eastern China (EC) could reduce extreme heat by altering energy and water budgets. However, the irrigation effect on increasing humidity has often been missed, especially in humid regions, leaving its effect and mechanism on extreme humid heat (EHH) poorly characterized. We analyzed assemblies of observations and performed regional simulations with more detailed irrigation scheme to explore the irrigation impacts and potential mechanisms on EHH. We find that irrigation in EC, despite having a cooling effect of about 0.2-0.6 degrees ${}<^>{\circ}$C, leads to an increase of about 0.4-0.8 degrees ${}<^>{\circ}$C in EHH, with a more intense impact on the Middle-Lower Yangtze Plain (MLYP) by 0.9 degrees ${}<^>{\circ}$C. Cooling effect induced by increased latent heat fluxes through irrigation contributes to air deposition, which lowers boundary layer height, raises near-surface moist enthalpy, and ultimately exacerbates the EHH. Results mechanistically emphasized irrigation impacts on EHH and highlighted the necessity of improving irrigation modeling reality.