Numerous studies have established that green spaces are crucial in combating urban heat islands (UHI). As ecological Green Hearts have been adopted in many multipolar urban agglomerations, this study questions their long-term impact on urban heat mitigation. Taking the “Green Heart” area of the Changsha-Zhuzhou-Xiangtan urban agglomeration, and utilizing land use datasets between 1990 and 2020, numerical simulations of near-ground air temperatures were conducted to analyze the temperature variations induced by the spatial dynamics and the land-use change inside the Green Heart. The findings reveal a 0.4 °C increase in urban temperatures caused by urban expansion. A “cool island effect” by the Green Heart is observed but the temperature difference achieved (2 °C to 4 °C) is no more significant than in city-scale parks and the cooling extent beyond the Green Heart's perimeter was insignificant. Doubling the construction land inside the Green Heart increased daytime and nighttime temperatures by 1.5 °C and 2.6 °C, respectively, suggesting the importance of maintaining forests. The long-term urban temperature fluctuations are arguably influenced more by the spatial transformations inside the cities than changes inside the Green Heart. These results imply that combating urban heat should prioritize city-centered cooling strategies and land-use control.

中文翻译：

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“绿心”夏季降温影响研究——基于天气研究预报（WRF）模拟的长株潭城市群案例研究


大量研究已经确定，绿色空间对于对抗城市热岛 （UHI） 至关重要。由于生态绿心已被许多多极城市群采用，本研究质疑它们对城市热缓解的长期影响。以长株潭城市群的“绿心”区域为研究对象，利用 1990 年至 2020 年的土地利用数据集，对近地空气温度进行了数值模拟，分析了绿心内部空间动力学和土地利用变化引起的温度变化。研究结果显示，城市扩张导致城市温度升高 0.4 °C。观察到绿心的“冷岛效应”，但达到的温差（2 °C 至 4 °C）并不比城市规模的公园更显着，而且绿心周边以外的冷却程度微不足道。将绿心内的建筑用地增加一倍，白天和夜间温度分别增加了 1.5 °C 和 2.6 °C，这表明维护森林的重要性。可以说，城市内部空间变化对城市长期温度波动的影响大于“绿心”内部的变化。这些结果表明，对抗城市热量应优先考虑以城市为中心的冷却策略和土地利用控制。