How to use lake breeze circulations to improve urban natural ventilation: A case study in a typical inland multi-lake megacity

Utilizing lake breeze circulations (LBCs) to improve city breathability is one of the most promising nature-based solutions for inland cities under calm and stable weather conditions. Previous studies highlighted the LBC benefits from great-sized lakes to mitigate urban heat island effects at the regional scale. How cold air flows out from relatively small lakes to influence the heat transfer process within urban areas, however, remains unclear. Using the Weather Research and Forecasting (WRF) model, the temporal development of lake breezes (LBs) was simulated in Wuhan city on hot days with weak synoptic wind. We further explored the spatial structures of a single LBC and the interactions of multiple LBCs on a typical LB day. The results indicate that LBs occurred mostly in the morning, peaked around noon, and dissipated in the afternoon. The LB occurrence periods with high probability varied significantly with the lake size, shape, location, and distribution. Specifically, large lakes with simple shapes and aggregated distribution were more likely to develop and sustain LBs. There were distinct LBC flow regimes on different lakeshores, in which the perturbed LBC mainly on leeward lakeshores increased cool air penetrability compared with the strong LBC predominantly on windward lakeshores. In addition, chain flows of LBCs formed over lake groups parallel to the prevailing synoptic wind, as the upper-level outflows from one upwind LBC were connected to the lower-level inflows from the other downwind LBC. Based on these results, we propose a conceptual framework for planning urban blue space to enhance natural ventilation, which can support urban planners to create livable built environments with lake breezes entry.