Urbanization Effect on Trends of Extreme Temperature Indices of National Stations over Mainland China, 1961–2008

TLDR

Long‑term changes in extreme temperature events are key for climate change detection, yet the influence of urbanization on extreme temperature index trends across China remains unclear. The study evaluates how urbanization has affected trends of extreme temperature indices in mainland China from 1961 to 2008 using a homogenized national temperature dataset and a rural station network. The authors used a homogenized daily temperature dataset from national reference and basic meteorological stations, combined with a rural station network, to assess urbanization impacts on extreme temperature index trends. Urbanization has driven significant trends in extreme temperature indices: annual Tmin, Tmax, and mean temperatures increased by 0.070 °C, 0.023 °C, and 0.047 °C per decade, respectively; diurnal temperature range declined sharply, especially in winter and spring; cold nights fell by 1.485 days per decade while warm nights rose by 2.264 days per decade, with the largest impacts in northern China and during the 1966–76 deurbanization period.

Abstract

Abstract Understanding the long-term change of extreme temperature events is important to the detection and attribution of climate change. It is unclear, however, how much effect urbanization has had on trends of the extreme temperature indices series constructed based on the commonly used datasets on a subcontinental scale. Applying a homogenized daily temperature dataset of the national reference climate stations and basic meteorological stations, and a rural station network previously developed, urbanization effects on trends of extreme temperature indices in mainland China for the time period 1961–2008 are evaluated. It is found that 1) the country-averaged annual- and seasonal-mean extreme temperature indices series generally experience statistically significant trends; 2) annual-mean urbanization effects in the country as a whole are statistically significant for daily minimum temperature (Tmin), maximum temperature (Tmax), and mean temperature of Tmin and Tmax (Tavg), reaching 0.070°, 0.023°, and 0.047°C (10 yr)−1, respectively, with the largest values for annual-mean Tmin occurring in north China; 3) annual- and seasonal-mean urbanization effects for the declining diurnal temperature range (DTR) are highly significant, and the largest seasonal-mean DTR decline because of urbanization occurs in winter and spring; 4) annual-mean urbanization effects for the lowest Tmin, summer days, tropical nights, and frost days series are significant, but an insignificant urbanization effect is detected for icing days series; 5) urbanization has led to a highly significant decline of annual cold nights at a rate of −1.485 days (10 yr)−1 and a highly significant increase of annual warm nights at a rate of 2.264 days (10 yr)−1. Although urbanization effects are also significant for cold days and warm days, they are relatively smaller, and 6) the smallest absolute values of annual-mean urbanization effects for most of the indices series are found to dominantly appear during 1966–76, a well-known deurbanization period resulting from the Cultural Revolution.