Abstract: As a key factor affecting both ecosystem processes and human health, the long-term dynamics of the diurnal temperature range (DTR) and its underlying drivers remain poorly constrained, largely due to the scarcity of longterm observational data. Here, we developed the first tree-ring cellulose oxygen isotope (δ¹⁸O)-based reconstruction of May–October DTR for China's Sichuan Basin, spanning the period 1673–2022. The reconstruction reveals a significant increasing trend in DTR since approximately 1952, which contrasts with the general global pattern and highlights distinct regional heterogeneity. This observed DTR increase is primarily driven by an asymmetric warming pattern dominated by rising maximum temperature (TMAX), and is closely associated with local environmental factors including reduced cloud cover and decreased atmospheric humidity. Correlation and running correlation analyses demonstrate significant modulation of the reconstructed DTR by sea surface temperature anomalies in key ocean basins. We find that the El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) jointly modulate DTR variability through their influences on monsoon circulation and cloud–radiation processes, with the Atlantic Multidecadal Oscillation (AMO) playing a secondary role. Future projections based on CMIP6 models indicate continued DTR increases under high-emission scenarios, underscoring the combined effects of internal climate variability and anthropogenic forcing on regional climate risks.

Key words: Tree rings, Stable oxygen isotopes, Sichuan basin, El Ni?o-Southern oscillation