Precipitation over urban areas in the western Maritime Continent using a convection-permitting model
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This study investigates the effects of urban areas on precipitation in the western Maritime Continent using a convection-permitting regional atmospheric model. The Weather Research and Forecasting model was used to simulate the atmosphere at a range of spatial resolutions using a multiple nesting approach. Two experiments (with and without urban areas) were completed over a 5-year period (2008–2012) each to estimate the contribution of cities to changes in local circulation. At first, the model is evaluated against two satellite-derived precipitation products and the benefit of using a very high-resolution model (2-km grid spacing) over a region where rainfall is dominated by convective processes is demonstrated, particularly in terms of its diurnal cycle phase and amplitude. The influence of cities on precipitation characteristics is quantified for two major urban nuclei in the region (Jakarta and Kuala Lumpur) and results indicate that their presence locally enhances precipitation by over 30 %. This increase is mainly due to an intensification of the diurnal cycle. We analyse the impact on temperature, humidity and wind to put forward physical mechanisms that explain such changes. Cities increase near surface temperature, generating instability. They also make land-sea temperature contrasts stronger, which enhances sea breeze circulations. Together, they increase near-surface moisture flux convergence and favour convective processes leading to an overall increase of precipitation over urban areas. The diurnal cycle of these effects is reflected in the atmospheric footprint of cities on variables such as humidity and cloud mixing ratio and accompanies changes in precipitation.
KeywordsRegional climate modelling Precipitation Maritime Continent Urban climate Convection Convection-permitting models
This work was made possible by funding from the Australian Research Council (ARC) as part of the Centre of Excellence for Climate System Science (CE110001028), as well as the NSW Office of Environment and Heritage. Jason Evans was supported by the Australian Research Council Future Fellowship FT110100576. This work was supported by an award under the Merit Allocation Scheme on the NCI National Facility at the ANU. We are thankful to the European Centre for Medium-Range Weather Forecasts for providing ERA-Interim data. We also thank Dr. Thomas Chubb from Monash University (Australia) for making the Skew-T code publicly available.
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