Climatic warming in Shanghai during 1873–2019 based on homogenised temperature records

Xujiahui (XJH) station in downtown Shanghai holds the longest continuous daily temperature series in China, which is unique for assessing modern climate change and impacts but must be homogenised. The present work established a set of homogenised monthly and daily surface air temperature (SAT) series during 1873–2019 at XJH. Two major inhomogeneous break points (around 1954 and 1993) were identified in the original SAT series, which had been overlooked in previous works. The inhomogeneous biases were adjusted via the inter-station deviation analysis. The adjusted SAT series shows a warming trend of 1.9 °C per century compared with 1.7 °C per century in the original series. The multi-decadal variations of quasi-32-year and quasi-64-year periods are weaker in the adjusted series than in the original series, suggesting overestimated multi-decadal variability in the original data due to inhomogeneous biases. Relative to the early period 1873–1900, the recent decade (the 2010s) is warmer by 2.2 °C. Urbanisation has been responsible for approximately 19.3% of the rapid warming since the 1980s. The high and low SAT extremes exhibit significant warming, especially after the 1970s. The trend in the low SAT extremes in the adjusted series is substantially larger than that in the original series, implying that previous studies might underestimate the warming in cold extremes.