Nighttime urban boundary layer height in the urban weather generator: Analysis and dynamic modelling

Source abstract

The urban weather generator (UWG) is a lightweight simulation tool that predicts the urban heat island intensity. One limitation of the UWG is that it takes as an input parameter the nighttime urban boundary layer (UBL) height, which is a time-varying physical quantity that is very little known. To overcome this limitation, a dynamic model for the nighttime UBL height is implemented in the UWG. The effect of this model implementation is analyzed in detail. A primary analysis of the base UWG model reveals erratic behavior related to the nighttime UBL height. When the nighttime UBL height is low, spurious fluctuations occur. When it is high, the air temperature predictions are disconnected from the characteristics of the urban layout, which renders the model inappropriate for assessing the performance of urban heat mitigation strategies. The dynamic nighttime UBL height model reconnects the air temperature predictions to the characteristics of the urban layout and regulates the thermal behavior of the UBL to avoid spurious fluctuations. The model predicts nighttime UBL height values that optimize the UWG prediction accuracy; however, these values remain considerably low compared with measured nighttime UBL heights. The paper also highlights contradictions in the definition of the characteristic length input parameter, and a strong correlation between the predicted rural inversion strength and the urban heat island intensity.