A numeric study of regional climate change induced by urban expansion in the Pearl River Delta, China

Abstract

The Pearl River Delta region has experienced rapid urbanization and economic development during the past 20 years. To investigate the impacts of urbanization on regional climate, the Advanced Research core of the Weather Research and Forecasting (ARW-WRF) model is used to conduct a pair of 1-yr simulations with two different representations of urbanization. Results show that the reduction in vegetated and irrigated cropland due to urban expansion significantly modifies the near-surface temperature, humidity, wind speed, and regional precipitation, which are obtained based on the significance t test of the differences between two simulations with different urbanization representations at the 95% level. Urbanization causes the mean 2-m temperature over urbanized areas to increase in all seasons (from spring to winter: 1.7° ± 0.7°C, 1.4° ± 0.3°C, 1.3° ± 0.3°, and 0.9° ± 0.4°C, respectively) and the urban diurnal temperature range decreases in three seasons and increases in one (from spring to winter: -0.5° ± 0.3°C, +0.6° ± 0.3°C, -0.4° ± 0.2°C, and -0.8° ± 0.2°C, respectively). Urbanization reduces near-surface water vapor (1.5 g kg-1 in summer and 0.4 g kg-1 in winter), 10-m wind speed (37% independent of season), and annual total precipitation days (approximately 6-14 days). However, the total rainfall amount increases by approximately 30%, since the decrease in the number of days with light rain (8-12) is overcome by the increase in the number of days of heavy or extreme rain (3-6), suggesting that urbanization induces more heavy rain events over the urban areas. Overall, the effect of urbanization on regional climate in the Pearl River Delta is found to be significant and must be considered in any broader regional climate assessment. © 2014 American Meteorological Society.