Numerical Study of the Impacts of Urban Expansion on Meiyu Precipitation over Eastern China

The Yangtze River Delta (YRD) has experienced significant urban expansion in recent years, while the Meiyu belt of China has demonstrated a decadal northward shifting trend. Thus, it is of interest to assess how urban expansion affects Meiyu precipitation and hopefully to reveal the underlying physical mechanisms involved. In this study, the urban extents over the YRD in 2001 and 2010 are derived based on land use/land cover (LULC) category data and nighttime light image data. Two parallel groups of 10-summer (2001-2010) numerical simulations are carried out with the urban extents over the YRD in 2001 and 2010, respectively. The results show that the urban expansion in the YRD tends to result in increased (decreased) Meiyu precipitation over the Huaihe River (Yangtze River) basin with intensities of 0.2-1.2 mm day^-1. Further analysis indicates that the spatiotemporal pattern of the Meiyu precipitation change induced by the urban expansion resembles the third empirical orthogonal function (EOF) mode of the observed Meiyu precipitation. Analyses of the possible underlying physical mechanisms reveal that urban expansion in the YRD leads to changes in the surface energy balance and warming (cooling) of tropospheric (stratospheric) air temperature over eastern China. Anomalous upward (downward) motion and moisture convergence (divergence) over the Huaihe River (Yangtze River) basin occur, corresponding to the increases (decreases) of the Meiyu precipitation over the Huaihe River (Yangtze River) basin.