Examining the onset of spring in China

The onset of spring is a critical time in mid-latitude atmosphere-biosphere interactions. Deciduous plants resume growth after winter dormancy, and their activities cause land surfaces to become more active agents in energy and mass exchanges. The progress of spring plant development driving these changes can be conveniently monitored by observation of plant life-stage (phenological) events. Thus, phenological data can play a crucial role in understanding and monitoring springtime vegetation and climate dynamics, especially about potential changes over time. Although global-scale phenological monitoring is not yet possible, alternative strategies are available to assess these impacts. In this paper, a simple phenological model, driven by surface-level daily maximum-minimum temperatures is employed as a surrogate measure of the onset of spring in China. Contrasting with results from similar studies in North America and Europe, the onset of spring plant growth in China has no apparent change over 1959-1993. However, during the same period, last spring frost (-2.2degreesC) dates have become markedly earlier (by 6 d), with the greatest change occurring in the northeast portions of the country. First autumn frost dates have also become later (by 4 d), especially in north-central China. Combining these 2 changes, the frost period has decreased by 10 d over many northern regions of the country. A shorting frost period is consistent with decreasing diurnal temperature ranges and day-to-day temperature differences during spring and autumn in China, reported by previous research.