Response of Climatological Normals to Climate Warming in Guangdong, South China

Climatological normals are 30-year averages of meteorological variables and their derived statistics, which are not only used as predictors of future climate conditions, but are also used as climatic background of certain regions. Under the backdrop of climate warming, the decadal-updated-normals have also undergone changes. Therefore, it is essential to investigate the difference between the new (1991－2020) and the old (1981－2010) climatological normals in Guangdong Province. In this paper, based on data from 86 national meteorological observatories, the basic climate warming facts are revealed by analysis on temperature, thereafter, multiple climate indicators derived from daily temperature and precipitation are analyzed. Regarding temperature-derived indicators, the results show that in the new climatic stage, Guangdong Province experienced an increase of 3.9 days in the annual the average of high-temperature days and a decrease of 1.1 days in low-temperature days, while cold wave days decreased by 0.2 days, all reflecting the fact of climate warming. Precipitation patterns also shifted across different temporal scales: annually, seasonally, monthly, through the flood season, and during the "Dragon Boat Water" period. Notably, both rainstorm amount and rainstorm days increased whereas total rainfall and rainfall days decreased. Furthermore, the rainy season began an average of 5.0 days later in the new normal compared to the old. Multiscale analysis reveals that the temperature differences between the new and old climatological normals are primarily driven by a dominant linear warming trend, while precipitation differences are mainly dominated by interannual variability, which explains the insignificant change in annual total precipitation.