October 2024
What drives warming rates of extreme temperatures relative to the mean?
Local hydroclimate drives differential warming rates between regular summer days and extreme hot days in the Northern Hemisphere.
Image credit: Image courtesy of Abhishekh Srivastava, Department of Land, Air and Water Resources, University of California Davis, Davis, CA, USA.
Image caption: The infographic shows the role of land-atmosphere interactions driving the warming of extreme temperatures (summer maximum value of daily maximum temperature; TXx) relative to the mean (summer mean daily maximum temperature; TXm). The red (blue) arrows indicate positive (negative) trends. The length of the arrows indicates the magnitude of the trend. The top panel shows that where trends in the Bowen Ratio (ratio of sensible to latent heat flux) during mean and extreme days are small and comparable in magnitude, the TXx has a smaller positive trend than TXm. This thermodynamical mechanism is generally true for hyper-arid, arid, semi-arid, and moist regions. The bottom panel shows that where trends in the Bowen ratio are significantly higher on TXx days, the TXx has a bigger positive trend than TXm. This mechanism holds for dry-subhumid regions.
The Science
This work compares the warming rate of Northern Hemisphere summer hot extremes against the mean. The study finds that the warming rate of hot extremes relative to the mean is determined by the local hydroclimate conditions.
The Impact
Heat extremes pose significant challenges for different sectors of society and the economy, such as human health, agriculture, animal discomfort, and energy demand. Identifying regions where extremes are rising faster or will rise faster in the future informs decision-makers and policyholders to take necessary steps for planning and adaptation. The physical mechanism identified in this work is useful for process-based evaluation of climate models.
Summary
This work examines the warming rate of summertime extreme temperatures relative to the local mean in the Northern Hemisphere. The relative warming pattern of extreme temperatures is analyzed using a generalized extreme value distribution framework. This study shows extreme temperatures are rising slower than the local mean in generally arid and moist regions. In contrast, the extremes are rising faster than the local mean in dry-subhumid regions. The evaluation based on the response of the surface fluxes during mean and extreme heat days suggests that the local hydroclimate conditions drive the relative warming rates of extreme temperatures.
Contact
Abhishekh Srivastava
Assistant Project Scientist, Department of Land, Air and Water Resources, University of California Davis, Davis, CA, USA
asrivas@ucdavis.edu
Funding
This research was supported by the Office of Science, Office of Biological and Environmental Research of the US Department of Energy under contract no. DE-AC02-05CH11231 for the CASCADE Scientific Focus (funded by the Regional and Global Model Analysis Program area within the Earth and Environmental Systems Modeling Program). The work of C.B. and of P.A.U. is supported by the “PCMDI: An Earth System Model Evaluation Project” Science Focus Area (SFA) funded through the Regional and Global Climate Modeling Program of the Office of Science at the DOE, and is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.
Publications
Srivastava, A. K., Wehner, M., Bonfils, C., Ullrich, P. A., & Risser, M. (2024). Local hydroclimate drives differential warming rates between regular summer days and extreme hot days in the Northern Hemisphere. Weather and Climate Extremes, 45, 100709. doi: 10.1016/j.wace.2024.100709.