Local hourly trends in near-surface and land surface temperatures.

Essential Climate Variables, such as near-surface (T2m) and land surface temperatures (LST), are typically reported in Coordinated Universal Time (UTC) for global consistency. However, their diurnal variability leads to temperature trends that differ by the local hour, a factor not analyzed on the global nor regional scale. Using ECMWF ERA5-Land reanalysis data (1981-2022), we assess temperature trends by local hour and month. Our results show that the trends can change significantly during the day. LST and T2m warming or cooling trends peak in the afternoon, while showing large spatial variability across both hemispheres. Using MODIS observations, we show how the nominal Equator crossing times of TERRA and AQUA influence LST trends. These findings highlight the necessity of accounting for local time in climate assessments to improve adaptation strategies.