Spatiotemporal Characteristics and Trends of Climate Extremes in and Around the Yunnan Reach of the Nujiang River Basin

Daily observations from 14 stations and ERA5 reanalysis were used to examine temperature, precipitation, and wind extremes in and around the Yunnan reach of the Nujiang River Basin during 1991–2020. Twelve station indices, two reanalysis-derived wind indices, and circulation diagnostics describe their spatial, seasonal, and interannual variability. The regional annual maximum of daily maximum temperature (TXx) and annual minimum of daily minimum temperature (TNn) increased by 0.50 and 0.55 °C per decade, respectively. Warm-night and warm-day frequencies increased by 3.98 and 3.00 percentage points (pp) per decade, whereas cold-night and cold-day frequencies decreased by 2.67 and 2.87 pp per decade. Recorded wet-day precipitation had a fitted trend of −69.27 mm per decade (Newey–West 95% confidence interval: −110.03 to −28.51 mm per decade; p = 0.002), with considerable interannual variability (R2 = 0.135). Climatological wet-day precipitation ranged from 847.46 mm at Yunxian to 2016.39 mm at Longling over the study period. Using identical station thresholds and matched valid days, ERA5 warm-day, cold-night, and heavy-precipitation frequencies differed from observations by −5.89, +7.14, and +0.40 pp, respectively. ERA5 annual maximum hourly 10 m wind speed showed no significant regional trend (+0.01 m s−1 per decade; p = 0.791). Seasonal circulation and humidity fields provide context for the observed annual cycle of temperature and precipitation extremes. Overall, the station network shows a shift towards warmer temperature extremes and strong spatial contrasts in precipitation; ERA5 captures shared annual frequency variations while yielding different mean frequencies and event dates, supporting separate evaluation of temporal covariability and local event occurrence.