The effect of urbanization of Metro Manila, particularly on the amount of sensible heat flux, rainfall and temperature of selected urban and rural areas, was investigated using the Weather Research and Forecasting Version 3.4.1 (WRFV3.4.1) model. National Center for Environmental Prediction - Final (NCEP-FNL) grib1 data from 2000 to 2010 were used as inputs into the model for meteorological data. The Mann–Kendall trend test (M–K test) was utilized to verify the significance of the trends while Sen’s slope estimator was used to quantify the measured trends. Results showed that, on average, the sensible heat flux of Metro Manila is about 1.5 × 10⁸ Jm⁻² higher than in selected areas outside Metro Manila. The occurrence of an urban heat island (UHI) effect was detected in Metro Manila by comparing the difference in the minimum and maximum temperatures. For the selected urban and rural areas, the minimum and maximum temperature differences (relative to Metro Manila) are around 0.4 to 2.4 °C and 0.83 to 2.3 °C, respectively. Metro Manila recorded higher 11-year average values of rainfall during the summer season (8% to 64%), rainy season (15% to 305%), and transition season (8% to 232%) when compared with selected areas from 25 to 100 km from Manila. These results show that the sensible heat flux, temperature and rainfall in Metro Manila is affected by Metro Manila’s urbanization.

The three megacities namely Cebu City, Davao City and Manila City are considered as highly urbanized cities in the Philippines. The migration of the rural dwellers to these cities are the cause of fast urbanization. To meet the demand for housing, better roads and economic growth, the use of land was shifted from natural ecosystems (such as vegetation, parks, forest) into artificial environments (such as high-rise commercial and residential buildings). These changes in both population densities and land uses greatly alter the weather and climate of these areas. Studies show urbanization greatly affects local weather, particularly temperature and rainfall patterns of the urban and nearby rural areas. The development of Urban Heat Island (UHI) effect is also documented as this brings discomfort and health related issues among urban dwellers. Using the Diurnal Temperature Range (DTR) values of the selected cities, the researchers investigated the development of UHI. The meteorological parameters of the three cities were generated by the Weather Research and Forecasting Model (WRF). Results showed that there are more hot days during the hot and wet period than hot and dry periods as revealed by the values of Tmax. Manila was warmer than areas under study during the hot and dry period. Early morning (Tmin , 5-AM) temperature of Manila is hotter with mean value of 27.3°C. In general, among the three cities Davao had the coolest morning temperature by approximately 1°C – 3°C. The differences of DTR are ranging from 0.15°C to 1°C. The predominance of UHI is observed during the dry and wet period and weak during the cool and dry period. Overall, UHI development occurred for the entire period of study.