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-resolu-
tion model (2-km grid spacing) over a region where rain-
fall 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 over-all 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.
Fig. 7. Difference between WRF2 and WRF2 NoUrb in total precipitation in Java domain (a) and Malay Peninsula domain (b). Stippling
indicates that differences are statistically significant using a Wilcoxon test at a 99 confidence level using daily values. Urban areas in WRF2
are delimited by green contours
This page is maintaind by Jason Evans |
Last updated 29 November 2013