The Cooling Efficiency Factor Index (CEFI): a geostationary satellite metric for near-real-time monitoring of land-surface processes and environmental stress

The cooling efficiency of the land surface, i.e. its ability to dissipate absorbed radiation and moderate temperature rise, is expressed through its apparent heat capacity, a dynamic surface property that varies throughout the day in response to turbulent fluxes and boundary layer development. Under continuous clear-sky conditions, daytime changes in apparent heat capacity can be estimated from geostationary satellite observations, allowing the derivation of the Cooling Efficiency Factor Index (CEFI), a physically based metric characterizing the local temperature response to incoming radiation at spatial scales of few kilometers. The spatial distribution of CEFI is primarily controlled by land cover and further modulated by evapotranspiration and near-surface wind speed, enabling the detection of microclimatic contrasts that are not resolved by conventional meteorological and climate products. Temporal variations in CEFI provide useful proxies for surface processes that are otherwise difficult to observe directly. In vegetated systems, CEFI acts as an indicator of drought stress associated with stomatal closure under soil moisture limitation and high atmospheric evaporative demand, and is therefore strongly related to vegetation productivity. In arid and sparsely vegetated regions, CEFI can serve as a direct proxy for surface wind stress. Here we present the theoretical background of CEFI and demonstrate the feasibility of several practical applications, including early detection of flash drought, estimation of wildfire risk in natural ecosystems, assessment of crop production losses, and identification of dust formation hotspots in desert environments. CEFI is available in near real time, providing suitable data to support operational environmental monitoring and early warning systems.