PNNL

Abstract

Reanalysis datasets provide spatially and temporally complete climate fields and are widely used as observational surrogates. Temperature trends from these datasets underpin numerous geoscience studies, yet the alignment of their directional trends with observations at the continental scale remains unclear. This study evaluates the directionality of annual mean daily maximum (TMAX) and minimum (TMIN) temperature trends from three reanalysis data, viz. ERA5, MERRA-2, and NLDAS against long-term observations at 7,059 (TMAX) and 6,983 (TMIN) stations across the continental United States (CONUS). We observe substantial trend misalignment, with ~27–30% of TMAX and ~21–30% of TMIN stations exhibiting discrepancies, mainly driven by false positive trends. Misalignment intensifies with longer records (=10–30 years) and is concentrated at stations with strong negative observed trends. Snow-affected regions show greater discrepancies, particularly in NLDAS. These findings call for caution while using reanalysis datasets for regional temperature trend analyses and derived applications.