Mechanism of Precipitation Increase with Urbanization in Tokyo as Revealed by Ensemble Climate Simulations

Abstract

This study examines how urbanization affects the precipitation climatology in Tokyo, Japan. A unique aspect of this study is that an ensemble, regional climatological simulation approach is used with sensitivity experiments to reduce uncertainty arising from nonlinearity in the precipitation simulations. Another aspect is that the robustness of the precipitation response is tested with ''stress response'' simulations with increasing urban forcing. The results show that urbanization causes a robust increase in the amount of precipitation in the Tokyo metropolitan area and a reduction in the inland areas. These anomalies are statistically significant at the 95% and 99% levels in some parts. There is no measureable change in the surrounding rural and ocean areas. These precipitation responses are attributed to an increase of surface sensible heat flux in Tokyo, which destabilizes the atmosphere and induces an anomalous surface low pressure pattern and the convergence of grid-scale horizontal moisture flux. The anomalous convergence of grid-scale horizontal moisture flux is a consequence of urbanization modifying the sea breeze.

Interaction of Urban Heating and Local Winds During the Calm Intermonsoon Seasons in the Tropics

“…The interactions of strong urban thermals with the natural topographic flow are analogously observed in inland and coastal cities (Freitas et al, ; Li et al, ; Miao et al, ; Ryu & Baik, ). As a result, the displacement or weakening/strengthening of these flows has significantly altered the rainfall patterns (Dixon & Mote, ; Kusaka et al, ; Thielen et al, ) and pollutant level within and around the city (Ji, Lee, & Lee, ; Thompson, Holt, & Pullen, ). The influence of urban thermals is further extended and complicated by the near proximity of urban to mountains and water body (Von Glasow et al, ).…”

Role and Impact of the Urban Environment in a Numerical Forecast of an Intense Summertime Precipitation Event over Tokyo

“…Its urban surfaces have often been argued to locally increase summertime precipitation (e.g., Fujibe et al 2009) as a result from an increase in low-level convergence over the city associated with enhancement of the Tokyo Bay breeze (e.g., Souma et al 2013, Kusaka et al 2014. In other meteorological situations the city has been shown to lead to the opposite effect, i.e., to a decrease in precipitation (i.e., Matheson and Ashie, 2008).…”

Impact of an improved WRF urban canopy model on diurnal air temperature simulation over northern Taiwan

“…Furthermore, the most recent report on world urbanization prospects published by the United Nations indicated that in 2014, 54 % of the world's population resided in urban areas (http://esa.un.org/unpd/wup/ Highlights/WUP2014-Highlights.pdf); by 2050, the world's urban population is projected to be 66 %. Rapid urbanization has resulted in environmental problems including increasing energy consumption and air pollution, deterioration of visibility, a significant urban heat island (UHI) effect, urban heavy rainfall, and even local (regional) climate change (Oke, 1982;Grimmond and Oke, 1995;Atkinson, 2003;Arnfield, 2003;Jin et al, 2005;Feddema et al, 2005;Ren et al, 2007;Corburn, 2009;Kusaka et al, 2012bKusaka et al, , 2014Kang et Published by Copernicus Publications on behalf of the European Geosciences Union.…”