Air temperature trend analysis for the Cananéia–Iguape Coastal System (São Paulo State, Brazil), 1981–2022, using reanalysis products evaluated against surface observations

This study addresses the scarcity of long-term climatic data in the Cananéia–Iguape Coastal System (CICS) by identifying a validated reanalysis-based framework for coastal climate monitoring. We evaluate which ECMWF product (ERA5, ERA5-Land, and AgERA5) best represents regional conditions against station observations (2007–2022). Our findings establish AgERA5 as the superior product for this coastal interface, overcoming the land–sea mask limitations of ERA5-Land. Using this validated series (1981–2022), we identify a pivotal climatic breakpoint in the year 2000, marking a transition to a significantly warmer regime. Annual trends show a persistent increase of 0.022 °C year⁻¹ (ranging from 0.02 °C year⁻¹ to 0.03 °C year⁻¹), with a pronounced seasonal asymmetry where September records the largest warming (0.05 °C year⁻¹). By providing a justified reanalysis choice and identifying a coherent regime shift, this study establishes a validated climatic baseline that can support future studies on potential ecosystem responses. • Four-station validation of ERA5, ERA5-Land, and AgERA5 air temperature over CICS. • AgERA5 outperforms ERA5 and ERA5-Land in reproducing monthly and seasonal air temperature across CICS. • A robust breakpoint around 2000 marks a shift toward warmer conditions across CICS. • Warming is seasonally asymmetric in CICS, peaking in JFM, JAS, OND, and in September–October.