Numerical Evaluation of the Impact of Urbanization on Summertime Precipitation in Osaka, Japan

Abstract

This study utilized the Weather Research and Forecasting (WRF) model version 3.5.1 to evaluate the impact of urbanization on summertime precipitation in Osaka, Japan. The evaluation was conducted by comparing the WRF simulations with the present land use and no-urban land use (replacing “Urban” with “Paddy”) for August from 2006 to 2010. The urbanization increased mean air temperature by 2.1°C in urban areas because of increased sensible heat flux and decreased mean humidity by 0.8 g kg−1because of decreased latent heat flux. In addition, the urbanization increased duration of the southwesterly sea breeze. The urbanization increased precipitation in urban areas and decreased in the surrounding areas. The mean precipitation in urban areas was increased by 20 mm month−1(27% of the total amount without the synoptic-scale precipitation). The precipitation increase was generally due to the enhancement of the formation and development of convective clouds by the increase in sensible heat flux during afternoon and evening time periods. The urbanization in Osaka changes spatial and temporal distribution patterns of precipitation and evaporation, and consequently it substantially affects the water cycle in and around the urban areas of Osaka.

Numerical Simulation of Heavy Rainfall in August 2014 over Japan and Analysis of Its Sensitivity to Sea Surface Temperature

“…The MSM GPV data have spatial resolutions of 0.0625 • (longitude) × 0.05 • (latitude) for ground level data and 0.125 • (longitude) × 0.1 • (latitude) for pressure level data and a temporal resolution of 3 h. The RTG_SST_HR data have a spatial resolution of 0.0833 • and a temporal resolution of 24 h. The FNL data have a spatial resolution of 1 • and a temporal resolution of 6 h. The physical parameterizations used in this study include the Yonsei University scheme [44] for the planetary boundary layer parameterization, the WRF single-moment 6-class microphysics scheme [45], the Noah land surface model [46], the rapid radiative transfer model [47] for long wave radiation, and the Dudhia scheme [48] for the shortwave radiation. Previous studies [40,49] showed that WRF accurately reproduced meteorological fields in Japan with these physical parameterizations. However, because Shimadera et al [40] also mentioned that there were difficulties in simulating summertime precipitation accurately at a certain time and location, this study evaluated the WRF results mainly by spatially integrated values.…”

“…Previous studies [40,49] showed that WRF accurately reproduced meteorological fields in Japan with these physical parameterizations. However, because Shimadera et al [40] also mentioned that there were difficulties in simulating summertime precipitation accurately at a certain time and location, this study evaluated the WRF results mainly by spatially integrated values. Further studies with different physical parameterizations may enable the improvement of the model performance for summertime precipitation.…”

“…Static geographical data, objective analysis data, and physical parameterizations used in this study were similar to those used by Shimadera et al [40]. Topography and land use were derived from the 30-s resolution data of the United States Geological Survey and the 100-m resolution National Land Numerical Information data of the Geospatial Information Authority of Japan, respectively.…”

“…The model performance was evaluated using the Pearson's correlation coefficient (r), the mean bias error (MBE), the mean absolute error (MAE), the root mean square error (RMSE), and the index of agreement (IA). IA is defined by [55]), and also Japan (Shimadera et al [40,49]). …”

Evaluation of Water Retentive Pavement as Mitigation Strategy for Urban Heat Island Using Computational Fluid Dynamics

“…The vertical domain consists of 30 layers from the surface to 100 hPa with the middle height of the first, second and third layers are about 28 m, 92 m and 190 m above the surface, respectively. Except for the calculation period, the WRF configurations were essentially the same as those in Shimadera et al (2015), the Yonsei University planetary boundary layer scheme , the WRF singlemoment 6class microphysics scheme (Hong and Lim, 2006), the Noah land surface model (Chen and Dudhia, 2001), the rapid radiative transfer model (Mlawer et al, 1997) for the long wave radiation, and the shortwave radiation scheme of Dudhia (1989) with initial and boundary conditions derived from the mesoscale model grid point value data by the Japan Meteorological Agency (JMA).…”