Revealing the response of urban heat island effect to water body evaporation from main urban and suburb areas

Abstract

The urban heat island (UHI) effect is accelerated with urbanization and climate change, thus threatening human survival. The evaporation from water body (E) takes away energy through heat absorption process, thereby effectively play a role in temperature cooling and UHI effect alleviation. However, the response of UHI effect to urban E is still lacks study in the current UHI research. To address this issue, this work proposes a customized water body evaporation model in urban areas. The newly developed urban E model considers the contribution of anthropogenic heat flux (AHF) to the energy balance in urban areas. Meanwhile, AHF is also used to enhance the simulation of the water heat storage change (G) for urban water body. Validation results in two megacities in China indicate that the developed urban E model which considered AHF in the energy balance equation significantly improves the simulation performance of E in the main urban area (the root mean square error (RMSE) significantly decreased by 26.6 W/m2 compared with the original Penman formula for E in the main urban area (Eu) simulation). The consideration of AHF in the G determination improves the simulation performance of E in the deep water body (the RMSE significantly decreased by 33.3 W/m2 compared to the AHF-Penman model that do not considering G for E simulation in deep water body). The developed urban E model is further used to evaluate the response of UHI to the Eu and E in the suburban area (Es). It is found that Eu effectively alleviates UHI, while Es aggravate UHI. Moreover, the cooling effect of E in the main urban areas (ΔTau) and suburbs (ΔTas) are increased with urbanization. The increasing rate of ΔTau is higher than ΔTas, indicate the contribution of evaporation cooling to the UHI alleviation is increased with urbanization. Further analysis demonstrate the urbanization process can explain approximately 90% of the enhanced ability of E to mitigate the UHI effect. Correlation analysis shows that the mitigation capability of E to UHI effect is mainly controlled by the volume and surface size of water body. Finally, future climate scenario-based urban E forecast confirms that ΔTau and ΔTas will continue to rise with climate change. The average increasing rate are 0.018 °C/year and 0.013 °C/year for ΔTau and ΔTas, respectively, under the three representative concentration pathways. The increasing rate of ΔTau is larger than ΔTas, suggesting the mitigation of the UHI effect will benefit more from urban E under the future climate change. Generally, our findings highlight that the mitigation of the UHI effect mainly benefits from E in the main urban area rather than E in the suburban area. This study gains insight into E in urban areas, including its algorithm, interaction with the UHI effect, and responses to urbanization and climate change. The results of this study provide a good scientific basis for urban landscape water planning.