In this Science Talk, Dr. Mohammad Reza Alizadeh, Senior Fellow at UNU-INWEH, examines how the land surface shapes the severity and persistence of climate extremes. Soil moisture governs how much incoming energy leaves the surface as evaporation and how much heats the air above it. Once soils dry past a threshold, evaporation can no longer buffer the surface energy balance. Temperature and atmospheric dryness then rise together, and a moderate rainfall deficit can develop into a compound dry-hot event lasting weeks.
Dr. Alizadeh will trace this land–atmosphere coupling from long-term observations to satellite records. A century of station data across the contiguous United States shows that compound dry and hot extremes have grown more frequent and more spatially connected. Satellites resolve the mechanism behind that trend: SMAP measures surface soil moisture and vegetation water content, ECOSTRESS resolves evapotranspiration and canopy temperature, and solar-induced fluorescence tracks photosynthesis as water stress develops. The consequences reach beyond temperature. Carbon uptake falls when stomata close under high atmospheric dryness, so the events that intensify heat also weaken the land carbon sink. Because soil moisture is observable from space within days, it is early enough to support drought and heat warning for agriculture and water management.
You may watch the talk on the UNU-INWEH YouTube channel (no registration required).
Speaker
Dr. Mohammad Reza Alizadeh
Research Fellow, Human-Environment Systems Modeling at UNU-INWEH
