Assessing the Impact of the Urban Landscape on Extreme Rainfall Characteristics Triggering Flood Hazards

Abstract

This study configures the Weather Research and Forecasting (WRF) model with the updated urban fraction for optimal rainfall simulation over Kampala, Uganda. The urban parameter values associated with urban fractions are adjusted based on literature reviews. An extreme rainfall event that triggered a flood hazard in Kampala on 25 June 2012 is used for the model simulation. Observed rainfall from two gauging stations and satellite rainfall from Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) are used for model validation. We compared the simulation using the default urban fraction with the updated urban fraction focusing on extreme rainfall amount and spatial-temporal rainfall distribution. Results indicate that the simulated rainfall is overestimated compared to CHIRPS and underestimated when comparing gridcell values with gauging station records. However, the simulation with updated urban fraction shows relatively better results with a lower absolute relative error score than when using default simulation. Our findings indicated that the WRF model configuration with default urban fraction produces rainfall amount and its spatial distribution outside the city boundary. In contrast, the updated urban fraction has peak rainfall events within the urban catchment boundary, indicating that a proper Numerical Weather Prediction rainfall simulation must consider the urban morphological impact. The satellite-derived urban fraction represents a more realistic urban extent and intensity than the default urban fraction and, thus, produces more realistic rainfall characteristics over the city. The use of explicit urban fractions will be crucial for assessing the effects of spatial differences in the urban morphology within an urban fraction, which is vital for understanding the role of urban green areas on the local climate.

The Atmospheric Dynamics Related to Extreme Rainfall and Flood Events during September-October-November in South Sulawesi

“…Nevertheless, the lowest values were determined in Palopo, Enrekang and Parepare (Tradowsky et al, 2023) on Figure 4b. The average annual rainfall (RTOT) confirmed a range of values between 1500 mm to 3500 mm per year (Umer et al, 2023) on Figure 4c. The wettest areas with an average rainfall of 3000 -3500 mm per year were observed along the western region of South Sulawesi, incorporating areas from Barru to Gowa (excluding Makassar) and the northern regions (Luwu Timur, Luwu Utara and Toraja Utara).…”

Modern Developments in Flood Modelling

“…The paper "Assessing the Impact of the Urban Landscape on Extreme Rainfall Characteristics Triggering Flood Hazards" [10] by Yakob Umer, Victor Jetten, Janneke Ettema and Gert-Jan Steeneveld presents a configuration of the WRF model developed for the city of Kampala, Uganda. The use of the WRF model to study the deep convection over Kampala required a special configuration, which requires the proper position and extent of the city in order to better consider the spatial contrast between the city and Lake Victoria.…”

Changing Urban Temperature and Rainfall Patterns in Jakarta: A Comprehensive Historical Analysis

“…Furthermore, increasing urban temperatures due to LULC change can influence urban rainfall. Urban-induced rainfall is a complex process, intricately influenced by the urban environment [23][24][25][26]. Temperature changes in urban areas are related to urbanization and global warming, which can affect local precipitation [27].…”

“…Marelle et al (2020) [35] showed that an increasing upward movement of warm air and moisture convergence to an increasing sensible heat could be an important driver of increasing rainfall due to urbanization. Umer et al (2023) [25] showed that changes in an urban landscape dominated by urban and built-up areas increased extreme rainfall intensity resulting in flash floods in the city of Kampala, Uganda. Future urbanization and LULC changes are projected to sustain an increase in urban rainfall, as observed in Can Tho, Vietnam [37], as well as in cities like Paris and Shanghai [38], along with numerous other urban centers worldwide.…”