Accurately monitoring urban precipitation is notoriously difficult, even more so in many parts of Africa where the coverage of ground-based weather radars is usually sparse. The built-up environment near radars may result in underestimation due to beam blockage and local overestimation due to clutter. In addition, due to the strongly varying urban canopy and terrain, rainfall measurements from gauges are often only representative for an even smaller area than in rural terrain. At the same time, accurate and timely precipitation measurements and, consecutively, forecasts are crucial because the response time of urban catchments is very fast and costs associated with potential damage are high.

Coincidentally, urban areas with high population density can generally be associated with high mobile phone traffic, which in turn requires a high density of cell phone towers to transmit the signals. The wireless connection between two cell phone towers, more commonly referred to as a Commercial Microwave Link (CML), is known to be (partially) attenuated by rainfall. Deriving the magnitude of the attenuation from the transmitted and received signal levels stored operationally in the network management system of mobile network operators, one can estimate the average rainfall intensity over the path. 

In this study we use a dense network of several thousand CMLs in the megacity of Lagos, Nigeria, to estimate path-averaged rainfall intensities. We employ the open-source R package RAINLINK to process the 15-minute CML data into path-averaged rainfall intensities, and, where available, evaluate these against dedicated rain gauge measurements and satellite precipitation retrievals. In addition, based on the CML-derived rainfall intensities, 2D rainfall maps are created using a geostatistical interpolation method. This study highlights both the benefits and complexities of using a very dense network of CMLs with, predominantly, a sub kilometer path length and limited reference rainfall data. 

How to cite: Walraven, B., Droste, A., Overeem, A., Bogerd, L., Leijnse, H., Coenders, M., Hut, R., van der Valk, L., and Uijlenhoet, R.: High-resolution urban precipitation monitoring in a tropical megacity using Commercial Microwave Links (CMLs), 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-943, https://doi.org/10.5194/icuc12-943, 2025.

                  Observed Link Between Spatial Pattern of Heavy Precipitation in Urban Cluster and Environmental Factors in the Greater Bay Area

Zheyu He^a, Jiachuan Yang^{a, *}

^a Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China

Global urbanization has rapidly increased over the past few decades, leading to the emergence of urban clusters comprising multiple adjacent cities and their surrounding areas. The Greater Bay Area (GBA) is one of the most urbanized clusters in China. Research indicates that urbanization processes—such as the urban heat island (UHI), building barrier effect, and aerosol emissions—significantly alter precipitation patterns in both urban and surrounding regions. However, most existing studies have primarily focused on the precipitation modifications in individual cities due to singular factors, often emphasizing the enhancement of precipitation occurring downwind of urban centers.

This study focuses on the GBA urban cluster, utilizing observational and reanalysis data to examine the spatial patterns of regional heavy precipitation events during the warm season (May-Sep) from 2010 to 2017 under varying conditions of regional UHI and ambient wind speed. Quantitative indicators, including horizontal and vertical precipitation profiles and regional precipitation anomaly ratios, were employed to analyze and compare the spatial distribution of precipitation between the central urban area and surrounding suburbs, as well as across different directions and distances from the urban center. This research investigates the potential link between extreme precipitation events in urban cluster and UHI under varying ambient wind conditions, thereby addressing gaps in the current literature regarding how urban clusters influence precipitation distribution in complex environments.

How to cite: He, Z. and Yang, J.: Observed Link Between Spatial Pattern of Heavy Precipitation in Urban Cluster and Environmental Factors in the Greater Bay Area, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-18, https://doi.org/10.5194/icuc12-18, 2025.

The United States Department of Energy-funded Community Research on Climate and Urban Science (CROCUS) Urban Integrated Field Laboratory is a multi-year intensive research program that integrates long-term instrumentation deployments, intensive field observations, and multi-scale modeling efforts across the greater Chicago region to study the community-scale physics and impacts of extreme weather and climate events. Set to occur in the spring of 2025, the CROCUS Urban Flooding and Rainfall Campaign is the second intensive field observation effort. The campaign’s goal is to use novel observational strategies to characterize hydroclimate dynamics from the subsurface through the troposphere before, during, and after flooding events in Chicago to enable physical and agent-based modeling, assess the performance of flood management infrastructure, and improve the resilience of Chicago-area residents to extreme precipitation events.  

Conducted in partnership with organizations within and around the city of Chicago, this campaign will collect a suite of subsurface, surface, and remote sensing observations at high temporal and spatial scales to benchmark remote sensing, parameterize multi-scale atmospheric and hydrologic models, and provide detailed data mapping for decision-making around the heterogeneity of the region’s flood response. Long-term monitoring of the subsurface and surface conditions across the region will be augmented by targeted soil characterization and soil moisture measurements and the deployment of an X-Band radar, soundings, lidars, and radiometers. Together, these observations will be used to drive coupled models to better understand the drivers for extreme precipitation in an urban setting, as well impacts of heavy precipitation on urban communities. These data collection efforts are embedded within Chicago neighborhoods and neighboring communities, and are thus critically coordinated with education and community engagement efforts to develop the scientific inquiry and build capacity within heavily impacted communities.

How to cite: Hence, D., Berkelhammer, M., Packman, A., Nesbitt, S. W., Negri, C., Kotamarthi, R., Collis, S., Burbano, B., Garcia, M., Gonzalez-Meler, M., Lauer, A., Lee, J., McNicol, G., Park, S., Querubin, S., Sharma, A., and Wadwha, A.: The 2025 CROCUS Urban Flooding and Rainfall Campaign, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-484, https://doi.org/10.5194/icuc12-484, 2025.

Climate change has led to a significant increase in the intensity and frequency of extreme meteorological events, resulting a substantial increase in flood risk for a large part of China's monsoon region territory. In the north of China, rainfall is highly concentrated temporally and spatially, posing significant flood risks to numerous villages in mountainous watersheds. The SWMM model was coupled with the HEC-RAS two-dimensional hydrodynamic model to simulate the flood inundation levels of 38 villages in YongDingHe watershed under extreme precipitation conditions.

The results indicate: (1) In terms of overall flood risk, villages located downstream of the Qingshui River and at the exit of the YongDingHe River gorge have higher flood risks, and under the three future SSPs scenarios, peak river flow, the number of flooded villages, flooded area, and inundation depth all significantly increase. (2) In different SSPs scenarios, 40% to 72% of medium-sized villages will be flooded under the 100-year return period, while 35.2% of small settlements have no flood risk. (3) The risk of village inundation is sensitive with the distance from water bodies, while under the 100-year return period in the SSP126, SSP245, and SSP585 scenarios, the inundation area of water-distant villages is 56.8%, 54%, and 60.9% smaller than that of water- proximate villages, respectively..

Villages with relatively high overall risks should build intercepting ditches and slope vegetation buffer zones on slopes to intercept slope runoff and slow down the flow speed of floods. Ecological ponds should be constructed in low-lying areas to temporarily store floodwater. Dry stone check dams should be built in mountain stream valleys to reduce the water flow speed and disperse the flood energy. The layout of land use in and around the villages should be optimized and adjusted, and flexible land use functions should be arranged in low-lying areas.

How to cite: Sun, Z., Zheng, L., Wu, Q., Jiang, J., and Cui, Z.: Climatic Resilience of Mountainous Villages in Northern China: a Case of YongDingHe watershed, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-995, https://doi.org/10.5194/icuc12-995, 2025.

A comprehensive understanding of urban cloud dynamics is crucial, as changes in local cloud patterns impact energy and water cycles. Given the relatively limited research on urban cloud formation compared to urban precipitation, particularly in Southeast Asian cities, this study provides critical insights into the effects of urbanization on cloud formation over Greater Kuala Lumpur (GKL). Using Himawari-8 satellite observations (2016–2021) and Weather Research and Forecasting (WRF) model simulations incorporating a single-layer Urban Canopy Model (UCM), this study conducts a comprehensive analysis of urban cloudiness during the southwest monsoon (dry season, JJA) and northeast monsoon (wet season, DJF). Satellite observations reveal that urban areas in GKL consistently exhibit greater daytime cloud cover than the surrounding rural regions. At 15:00 local time (LT), peak urban cloudiness is 1.22 times greater than in rural areas during JJA and 1.24 times greater during DJF. These differences are primarily attributed to increased absorption of solar radiation and the urban heat island (UHI) effect, which enhance surface heating and convective activity. Numerical experiments further elucidate the mechanisms underlying this urban cloud enhancement. Urban areas exhibit significantly higher sensible heat fluxes (SH), with peak SH values reaching 1.4 times those of rural areas during both JJA and DJF. Consequently, the urban boundary layer height (PBLH) is consistently elevated, with average differences reaching approximately 530 m at 16:00 LT in DJF and 520 m at 18:00 LT in JJA. The diurnal evolution of PBLH closely follows SH variations, peaking around 15:00 LT. Enhanced boundary layer growth over urban regions fosters greater cloud fraction between 17:00 and 19:00 LT, reinforcing satellite-derived evidence of increased urban cloudiness. By integrating statistical and numerical approaches, this study enhances the understanding of urban cloud dynamics in tropical megacities, providing valuable insights for improving weather and climate predictions in rapidly urbanizing regions.

How to cite: Syed Mahba, S. F. and Kusaka, H.: Urbanisation-induced cloud enhancement over Greater Kuala Lumpur:  Evidence from satellite data and WRF-UCM model, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-546, https://doi.org/10.5194/icuc12-546, 2025.

Urban environments significantly modify boundary layer processes through spatial heterogeneities in surface heat and momentum fluxes. These heterogeneities are shaped by variations in building heights and land cover and impact the initiation, development, and evolution of convection, influencing precipitation patterns. The extent of these impacts varies under different synoptic weather conditions such as strong winds, weak winds, coastal marine environments, and low-level jets. This study aims to investigate how these local-scale processes interact with larger-scale weather patterns and affect organized convection in the coastal city of Houston, TX.

We conducted sub-kilometer scale simulations using the Weather Research and Forecasting (WRF) model coupled with the multi-layer BEP-BEM urban canopy model. The simulations featured a 3-D turbulent kinetic energy (TKE) scheme for vertical mixing, dynamically transitioning between large-eddy simulation (LES) and mesoscale parameterizations to address the gray-zone challenge. Two case studies were selected from the TRacking Aerosol Convection interactions ExpeRiment (TRACER): (i) a clear-sky day and (ii) a precipitation event.

Observational datasets from TRACER—including ceilometer-derived boundary layer heights, flux anemometer measurements of heat fluxes, radiosonde soundings, radar reflectivity, and surface meteorological observations—were used for model evaluation. Preliminary results indicate that the LES-based configuration captures spatial heterogeneities in near-surface meteorological fields. However, further analysis is required to understand how urban-induced heterogeneities affect the organization of convection and precipitation development under contrasting synoptic conditions.

This study highlights the need for refined experimental design to reveal the contrasting mechanisms across varying local and large-scale conditions. It also addresses key limitations related to parameterization schemes and grid resolution, offering insights for future improvements in urban weather prediction.

How to cite: Kamath, H., Pena, J. C., Zonato, A., Sudharsan, N., Gonzalez-Cruz, J., Yang, Z.-L., and Niyogi, D.: Urban Influence on Convection and Precipitation in the Coastal City of Houston, TX, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-964, https://doi.org/10.5194/icuc12-964, 2025.

While Singapore has demonstrated concerted efforts and progress in pluvial flood management, the recent Third National Climate Change Study in Singapore (V3) projects an increase in future annual extreme rainfall, and flash floods are expected to intensify. However, occurrences of flash floods in Singapore generally do not result in fatalities and significant infrastructural damages, and the most salient impacts observed during flash flood events are disruptions to traffic networks and businesses, which translates to economic and productivity losses.

This study thus aims to 1) Characterise future flooding likelihood and its uncertainties in Singapore under various Shared Socioeconomic Pathways (SSPs) for mid and end-century scenarios, 2) Calculate potential economic loss associated with travelling time delay due to traffic disruptions during flood events.

A Bayesian probabilistic modelling approach was used to obtain the probability distribution of flooding as a function of various precipitation intensity values (i.e. maximum 30, 60, and 120 minutes rainfall) for present day and across different SSPs scenarios. Travel routing simulations of vehicle and public transit were conducted for dry and flood conditions to determine the total travel time delay during flood conditions.

Results showed that future flood likelihood is the highest and has the most widespread impacts beyond the 99^th percentile of maximum 30 minutes rainfall, compared to other intense rainfall durations. Interestingly, flooding likelihood is higher for present conditions than future scenarios due to projected longer drier days and more intense but infrequent extreme precipitation.

Intensification of precipitation extremes in the future poses hard limits to pluvial flood prevention in Singapore, which has significant implications to policy. This indicates that continual infrastructural flood prevention measures have limited efficacy under extreme rainfall events, and cross-sectoral adaptation measures for extreme rainfall and pluvial flooding should be prioritised to enhance flood resilience in Singapore.

How to cite: Pak, H. Y., Chow, W., and Van Gevelt, T.: Future rainfall extremes and pluvial flood risk assessment in Singapore, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-532, https://doi.org/10.5194/icuc12-532, 2025.

Design storms are widely employed to evaluate flood risks in urban areas. These synthetic storms are not direct representations of real extreme rainfall events but are simplified simulations designed to mimic such extremes. Typically derived from rainfall intensity-duration-frequency (IDF) curves, design storms represent scenarios under specific extreme rainfall conditions. To adapt these storms for future climates, IDF curves must first be recalculated to reflect projected climatic changes. We present a framework for updating sub-daily to daily IDF curves and corresponding design storms based on projected changes in rainfall temperatures and rainfall occurrence at the daily scale; information that is readily available from global and regional climate models without the need to bias-correct or further downscale the climatic data. Our approach utilizes the TENAX (TEmperature-dependent Non-Asymptotic statistical model for eXtreme return levels) model, a novel physics-based statistical tool that estimates future return levels of short-duration rainfall. This enables the development of future rainfall intensity profiles and corresponding design storms using reconstructed IDF curves for the projected climate. We demonstrate this method by re-parameterizing the Chicago Design Storm (CDS) to account for climate change impacts, using Zurich (Switzerland) as a case study. Specifically, we calculate changes in the IDF curve for durations ranging from 10 minutes to 3 hours by applying the TENAX model to estimate future 100-year return levels. The resulting synthetic 100-year return period design storms are constructed for both present and future climates, allowing us to produce flood inundation maps and evaluate shifts in flood risk for the city under changing climatic conditions.

How to cite: Peleg, N. and Marra, F.: Simulating design storms in a changing climate: a physics-based approach to urban flood risk assessment, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-24, https://doi.org/10.5194/icuc12-24, 2025.

Urban areas can influence local precipitation patterns and amounts. While many earlier studies focused on the magnitude of precipitation modification by cities, this study develops a method to identify the source areas of the precipitation modification. This is illustrated for the western part of the Netherlands for 2017-2023. Radar-derived precipitation data is used to analyze precipitation anomalies, which are traced back to their source areas by determining the precipitation’s motion for each rainfall event. Using machine learning techniques, the influence of hypothesized causes – urban heat, air pollution, surface roughness, and their interactions – on precipitation anomalies is evaluated. We find that urban and industrial areas generally enhance precipitation downwind, while large rural areas tend to weaken it. Nearly 30% of the study area frequently generates enhanced precipitation downwind, with an average increase of 16.1% of the total precipitation. The identified source locations of precipitation modification are consistent for different seasons. We also find that surface roughness and SO2 concentrations (used as a proxy for air pollution) show a positive correlation with precipitation anomalies. Air pollution is the most influential predictor of precipitation anomalies in this study, followed by the interaction between air pollution and urban heat, and then surface roughness. Compound effects are less important contributors than the individual variables. This methodology provides a novel perspective on precipitation modification, offering a foundation to refine assumptions about source locations and improve understanding of the mechanisms driving the effect.

How to cite: van der Graaff, J. and Steeneveld, G.-J.: A new method to identify source areas of precipitation modification and their attribution: an illustration for the western Netherlands, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-848, https://doi.org/10.5194/icuc12-848, 2025.

In the context of global warming, in recent years, extremely heavy rains and subsequent flood damages have occurred more frequently. The objectives of this study are to propose city planning focused on flood damage mitigations and to investigate the mitigation effects of introducing such planning on the flood damages under projected future (the 2050s) climate conditions. Urban compactness and utilization of existing building stocks are taken into consideration in the planning. Those strategies are attracting much attention in Japan, where the population decline and severe financial condition are major social issues. The target area is Aichi Prefecture, which is the main prefecture in the third largest metropolitan area of Japan.

Two compact city plans are created in this study. In both city plans, urban compactness is achieved through population movement among urban areas (classification of population-withdrawal areas and population-induced areas). The withdrawal areas correspond to areas that will be exposed to severe flood damages in the events of future heavy rains. The two types of compact city plans, i.e., high-concentrated and low-concentrated plans, are made depending on the number of withdrawal areas. Moreover, for both city plans, existing building stocks in the population-induced areas are actively utilized to accommodate the population from the withdrawal areas.

The future (the 2050s) heavy rains and subsequent flood damages are projected using a coupling analysis of precipitation and runoff. A dynamical downscaling simulation technique is adopted to project the future climate including precipitation. The above-mentioned compact city plans are reflected by the settings of land use data and urban parameters as input conditions for the coupling analysis. Finally, the flood damage mitigation effects of the proposed compact city plans are quantitatively evaluated by comparing the extent and severity of flood damage with the results in case of using the current land use.

How to cite: Kondo, T., Iizuka, S., and Yamasaki, J.: Proposal for compact city plans focused on flood damage mitigations and investigation of their mitigation effects using a coupling analysis of precipitation and runoff, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-894, https://doi.org/10.5194/icuc12-894, 2025.