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Unexpected large-scale atmospheric response to urbanization in East China

Ma, Hongyun, Li, Tim, Jiang, Zhihong, Gu, Peng
Climate dynamics 2019 v.52 no.7-8 pp. 4293-4303
climatic factors, evaporation, land use, latitude, mathematical models, monsoon season, rain, specific humidity, subsidence, summer, surface temperature, tropics, urbanization, China
Urban land use in East China has undergone considerable change since the 1990s. How such change affects both in situ and remote climate conditions is investigated through numerical modelling experiments with the Community Atmosphere Model Version 5.1. The results show that urbanization causes an increase in surface temperature due to reduced surface albedo but a decrease in specific humidity due to locally reduced surface evaporation. The change in specific humidity overwhelms the surface temperature change effect, leading to locally reduced precipitation. It is noted that urbanization causes changes in climate conditions not only locally but also remotely. Anomalous low-level divergence associated with the reduced precipitation in situ prevents the northward progression of the East Asian summer monsoon. As a result, the major monsoon rain band is strengthened and confined over South China and the tropical Asian monsoon zone along 12°–25°N. The increase of rainfall in the tropical zone, on one hand, induces the local overturning cell, leading to anomalous subsidence over mid-latitude Asia and the equatorial zone, and, on the other hand, perturbs the Subtropical Jet, generating a Rossby wave train disseminating along the Jet. Both of these processes cause anomalous dry and hot conditions over mid-latitude Asia.