Urbanization effects on climatic changes in 24 particular timings of the seasonal cycle in the middle and lower reaches of the Yellow River

Abstract

Changes in the timing of the seasonal cycle are important to natural ecosystems and human society, particularly agronomic activity. Urbanization effects (UEs) on surface air temperature changes at the local scale can be strong. Quantifying the observed changes in the timing of the seasonal cycle associated with UEs or large-scale background climatic warming is beneficial for the detection and attribution of regional climate change and for effective human adaptation, particularly in China, where rapid urbanization and industrialization are occurring. In this study, long-term changes in 24 particular timings of seasonal cycle, known as the Twenty-four Solar Terms (24STs), in the middle and lower reaches of the Yellow River in China are analyzed on the basis of homogenized daily temperature data over 1961–2010. UEs on these changes are further assessed by using a rural-station network selected from 2419 meteorological stations. In terms of area mean, half of the 24STs have significantly warmed, and UEs have contributed to 0.07–0.14 °C/decade or 25.7–64.0 % of the overall warming. The climatic solar terms from mid-February to early May (September and early October) have significantly advanced (delayed) by 5–17 days (approximately 5 days) over the last 50 years; 2–4 (2–3) of these days are attributed to UEs. The contribution of urbanization to the advancing or delaying trends is 21.7–69.5 %. The implications of these quantitative results differ for farmers, urban residents, and migrant workers in cities.