Search

Simulations of five November months (2010–2014) using the urban version of the numerical weather prediction system of the Meteorological Service Singapore (uSINGV) are used to analyse the urban effect on convective precipitation over Singapore and Johor Bahru (Malaysia). The model is able to closely predict locations where rainfall peaks occur, but rainfall totals are overestimated compared to radar data. The temporal variability of rainfall in the region shows that urban areas increase the frequency and severity of rainfall events and that such impact increases with the rainfall intensity. Results show that low-level moisture advection is enhanced in this coastal conurbation as a result of the strengthening of wind convergence. The latter is likely caused by increasing sea-breeze strength due to lower surface pressure over the urban area, and higher urban surface roughness, respectively. As a consequence, more precipitable water is available in the region, enhancing convection and increasing the probability of heavy rainfall over the centre and north of Singapore island and Johor Bahru. Stronger convection further increases moisture advection from the vicinity. By studying the temporal variability and the spatial distribution of rainfall events, the present study provides new insights on the urban impact on heavy rainfall in tropical areas. The conclusions are only valid for the November inter-monsoon period, when local forcing, rather than large-scale influences, dominates rainfall generation. National Environment Agency - Singapore, R-109-000-338 236-490

Urban development exacerbates urban heat island effects of cities and thermal discomfort of the residents worldwide. However, such urban effects vary with the geographical and climatic conditions of the respective cities. This study is the first to quantitatively estimate the impact of past (1878), present (2012), and future (2050) urbanization on surface air temperatures and human thermal comfort in Sofia, the largest city of Bulgaria. We used the state‐of‐the‐art Weather Research and Forecasting (WRF) climate model, with a 1‐km horizontal resolution for three cases: LU1878, LU2012, and LU2050. We first validated the results of the control simulation (case LU2012) against actual observations. The model satisfactorily reproduced the diurnal variation of the observed monthly mean surface air temperatures for July (2011–2013) with a mean bias of ±0.6°C. We then estimated the potential impacts of past and future urbanization on surface temperature. Our results suggest that because of urbanization of Sofia, the surface air temperature at 0600 Local Standard Time (LST) has increased approximately 4.0°C in the past (1878–2012) and approximately 0.4°C in future (2012–2050). We also evaluated the impact of the urban thermal environment on human comfort levels. Considering the LU2050 case in the central part of Sofia, the temperature–humidity index during mid‐afternoon (1400–1700 LST) is estimated to be 24–26, indicating that approximately 50% of the residents could feel perceptibly uncomfortable.

Groundwater salinization is one of the most severe environmental problems in coastal aquifers worldwide, causing exceeding salinity in groundwater supply systems for many purposes. High salinity concentration in groundwater can be detected several kilometers inland and may result in an increased risk for coastal water supply systems and human health problems. This study investigates the impacts of groundwater pumping practices and regional groundwater flow dynamics on groundwater flow and salinity intrusion in the coastal aquifers of the Vietnamese Mekong Delta using the SEAWAT model—a variable-density groundwater flow and solute transport model. The model was constructed in three dimensions (3D) and accounted for multi-aquifers, variation of groundwater levels in neighboring areas, pumping, and paleo-salinity. Model calibration was carried for 13 years (2000 to 2012), and validation was conducted for 4 years (2013 to 2016). The best-calibrated model was used to develop prediction models for the next 14 years (2017 to 2030). Six future scenarios were introduced based on pumping rates and regional groundwater levels. Modeling results revealed that groundwater pumping activities and variation of regional groundwater flow systems strongly influence groundwater level depletion and saline movement from upper layers to lower layers. High salinity (>2.0 g/L) was expected to expand downward up to 150 m in depth and 2000 m toward surrounding areas in the next 14 years under increasing groundwater pumping capacity. A slight recovery in water level was also observed with decreasing groundwater exploitation. The reduction in the pumping rate from both local and regional scales will be necessary to recover groundwater levels and protect fresh aquifers from expanding paleo-saline in groundwater.

As an effect of climate change, cities need detailed information on urban climates at decision scale that cannot be easily delivered using current observation networks, nor global and even regional climate models. A review is presented of the recent literature and recommendations are formulated for future work. In most cities, historical observational records are too short, discontinuous, or of too poor quality to support trend analysis and climate change attribution. For climate modeling, on the other hand, specific dynamical and thermal parameterization dedicated to the exchange of water and energy between the atmosphere and the urban surfaces have to be implemented. Therefore, to fully understand how cities are impacted by climate change, it is important to have (1) simulations of the urban climate at fine spatial scales (including coastal hazards for coastal cities) integrating global climate scenarios with urban expansion and population growth scenarios and their associated uncertainty estimates, (2) urban climate observations, especially in Global South cities, and (3) spatial data of high resolution on urban structure and form, human behavior, and energy consumption.

Summary Extreme urban heat causes serious climatic, environmental, and economic problems. Daytime radiative cooling technologies are the most promising cooling technology in recent years. Here, we report experimental and numerical analysis to assess the cooling performance of scalable broadband radiative coolers, evaluate their heat mitigation potential in cities, and investigate their impact on local climate and the atmospheric dynamics. We show that, when air temperature reached its peak, the sub-ambient surface temperature of 8.2°C was achievable for samples with a wind cover. The maximum reductions of peak ambient temperature, average daytime ambient temperature, and highest urban canopy temperature are 5.3°C, 3.6°C, and 13°C, respectively. Collectively, we show that broadband coolers can significantly mitigate urban heat, but the cooling island effect they generate would increase side effects such as a decrease in the mixing layer of the atmosphere and an increase in pollutant concentration.

Short-term extreme rainfall events (EREs) often produce urban flooding and result in the loss of life and property. In this study, three high spatial-temporal resolution precipitation products were used to analyze hourly EREs during May-October from 2001 to 2018 over the Yangtze River Delta (YRD). To quantify the possible link between EREs and environmental factors (such as urbanization, climate change, and orography), the Hovmoller diagrams and Generalized additive model for location, scale, and shape (GAMLSS) nonstationary model were used. The results showed that the eastward propagating precipitation systems created a heavy rainfall center in the southwest mountainous of YRD due to orographic lifting, and enhanced in the plains over urbanized areas, especially in the vicinity of Nanjing, Changzhou, and Nantong metropolitan regions. The variability of hourly rainfall extreme in the urbanized regions is high correlated to the multivariate ENSO index (MEI), and shows a greater magnitude in the urban than rural regions. This phenomenon was intensified by large-scale circulation patterns due to strong-ENSO over the Nanjing-Changzhou-Nantong (NCN) urban regions, but weakened over the Shanghai-Hangzhou-Ningbo (SHN) urban regions. An analysis of nonstationary GAMLSS also suggests the large-scale circulation presents a greater impact on the hourly extreme rainfall than the urbanization, while the hourly rainfall extremes in the urban areas are still higher than that in rural regions under the nonstationary scenario. Those results suggest intense rainfall occurred more frequently in the urban region under observed climate change and urbanization in YRD.

This study examines the climate impact of future urbanization on the urban heat island effect over one of the developing megacities in tropical Southeast Asia, the greater Ho Chi Minh City area, using a dynamical downscaling approach with a high-resolution regional climate model coupled to urban canopy model. Simulations incorporate different land use/cover and anthropogenic heat release data sets for the current and future periods, while the boundary condition was fixed in the current time to detect only the impact of urbanization. Furthermore, human thermal comfort due to changes in the thermal environment was examined by analyzing the temperature-humidity index. Simulated results show that the increase in the surface air temperature is approximately 0.22 °C in the preexisting urbanized area and approximately 0.41 °C in new highly urbanized areas. The main factor in these changes is conversion from agricultural or grassland to urban structures, which results in increased sensible heating and decreased latent heating. Simulated results also show that despite the increase in air temperature, there is no significant change in thermal comfort. This is because human comfort is not only determined by temperature alone, but also by relative humidity. Urbanization increases temperatures, but decreases evaporation, which then decreases the relative humidity.

Meteorology and emission sources are the two main factors determining concentrations of air pollutants, including fine particulate matter. A regional air quality modeling system was used to analyze the sources of fine-particulate air pollution in Hanoi, Vietnam, in December 2010. The impacts of precipitation and winds on PM2.5 concentrations was investigated. Precipitation was negatively correlated with PM2.5 concentrations. However, winds showed both positive and negative correlations with PM2.5 concentrations, depending on wind direction (WD) and the level of upwind concentrations. Sensitivity simulations were conducted to investigate the contribution of local and non-local emissions sources on total PM2.5 by perturbing the emission inputs of the model. Overall, local and non-local sources contributed equally to the total PM2.5 in Hanoi. Local emission sources comprised 57% of the total PM2.5 concentrations for the high PM2.5 pollution levels, while only comprising 42% of the total PM2.5 for low levels of PM2.5 concentrations. In Hanoi&rsquo, s urban areas, local sources contributed more to the total PM2.5 than non-local sources. In contrast, non-local sources were the main contributors to the PM2.5 in Hanoi&rsquo, s rural areas. Additional sensitivity simulations were conducted to identify the main local emission sources of PM2.5 concentrations in December 2010. The industrial and residential sectors collectively comprised 79% of the total PM2.5 concentrations while the transport and power sectors comprised only 2% and 3%, respectively. This is the first case study which used a regional air quality modeling system to provide new and informative insights into PM2.5 air pollution in Hanoi by estimating the contributions of local and non-local emissions sources, as well as the contribution of local emission sectors to PM2.5 concentrations in Hanoi.

In this paper, we present the current exploitation status of the wind resources in general and of the offshore wind in particular. In addition, we introduce the initial and basic calculation of wind energy density at the height of 100 m, the method for development of wind resources, and the development of wind energy responding to climate change. The Vietnam sea region has a huge potential for wind energy resource in 0–30 m deep-water with an area of 111,000 km2 and a potential capacity of producing 64,000 GW and in 30–60 m deep-water with an area of 142,000 km2 and a potential capacity of producing 106,000 GW. The most promising region is the coastal area of Binh Thuan - Ca Mau provinces with a density of nearly 1000 W/m2, which is one of the high potential regions in the world. Wind farms have been deployed in this region with a total capacity of 1 GW and is expected to be 9 GW in 2030. We suggest that more research on and development of wind energy and zoning is needed to ensure energy security, reduce greenhouse gas emissions and mitigate the impact of climate change.

Tropical cities are more susceptible to the suggested fall outs from projected global warming scenarios as they are located in the Torrid Zone and growing at rapid rates. Therefore, research on the mitigation of urban heat island (UHI) effects in tropical cities has attained much significance and increased immensely over recent years. The UHI mitigation strategies commonly used for temperate cities need to be examined in the tropical context since the mechanism of attaining a surface energy balance in the tropics is quite different from that in the mid-latitudes. The present paper evaluates the performance of four different mitigation strategies to counterbalance the impact of UHI phenomena for climate resilient adaptation in the Kolkata Metropolitan Area (KMA), India. This has been achieved by reproducing the study sites, selected from three different urban morphologies of open low-rise, compact low-rise and mid-rise residential areas, using ENVI-met V 4.0 and simulating the effects of different mitigation strategies- cool pavement, cool roof, added urban vegetation and cool city (a combination of the three former strategies), in reducing the UHI intensity. Simulation results show that at a diurnal scale during summer, the green city model performed best at neighborhood level to reduce air temperature (Ta) by 0.7 °C, 0.8 °C and 1.1 °C, whereas the cool city model was the most effective strategy to reduce physiologically equivalent temperature (PET) by 2.8° – 3.1 °C, 2.2° – 2.8 °C and 2.8° – 2.9 °C in the mid-rise, compact low-rise and open low-rise residential areas, respectively. It was observed that (for all the built environment types) vegetation played the most significant role in determining surface energy balance in the study area, compared to cool roofs and cool pavements. This study also finds that irrespective of building environments, tropical cities are less sensitive to the selected strategies of UHI mitigation than their temperate counter parts, which can be attributed to the difference in magnitude of urbanness.