**5. Surfaces and materials**

Buildings' volume, orientation, and the aspect ratio of the spaces between them affect the exposure of urban surfaces to the solar radiation. The concentration of concrete structures without green surfaces between them increases the air temperature of urban areas. In this case study, the concentration of buildings is significantly higher in San Juan than in Gurabo, Puerto Rico (see **Figure 12**). The gray plots indicate the building structures in each city. At a first glance, it is observed that there is a greater amount of building structures in the city of San Juan. The city of San Juan has three times more building structures than the city of Gurabo. The city of San Juan has 127.98 km2 of the surface area of which 15.89 km<sup>2</sup> are of building structures. On the other hand, the city of Gurabo has 73.22 km2 of the surface area of which 3.33 km2 are of buildings.

**189**

heat (J/kgK).

**Figure 12.**

*Urban Heat Island Effects in Tropical Climate DOI: http://dx.doi.org/10.5772/intechopen.91253*

and are important to determine UHI.

*Building structures San Juan vs. Gurabo, Puerto Rico.*

the day and its slow release at night [12]. Thermal diffusivity (mm2

<sup>α</sup> = \_*<sup>k</sup>*

where *k* is thermal conductivity (W/mK), *ρ* is density (kg/m3

The complex heat exchange between buildings' mass and adjacent air changes the intensity and patterns of airflow in urban canyons where wind patterns are also affected by the canyon-like structure of streetscapes surrounded by tall buildings. Urban surface materials' thermal characteristics (specific heat, mass, conductivity, and diffusivity), color, texture, and coverage alter heat exchange in urban settings

Some construction materials have properties that tend to exacerbate the heat island problem. Two material properties are important to heat storage: thermal conductivity and heat capacity. Materials with high thermal conductivity tend to conduct heat into their depths. Materials with high heat capacity can store more heat in their volume. A combination of these properties, called thermal diffusivity, is an important indicator of how easily heat can penetrate a material. Thermal diffusivity is calculated by dividing a material's thermal conductivity by its heat capacity. Rural areas tend to be composed of materials of lower thermal diffusivity, while urban areas have higher diffusivities. This enhances the storage of heat during

Another significant material characteristic is the albedo. Urban areas are considered with a low albedo, while rural areas are considered with higher albedos. Most urban materials reflect less incoming solar energy than materials commonly found in rural areas. **Figure 13** shows differences of temperature between two widely used materials in Puerto Rico, such as asphalt and concrete, at 14:00 hours on a spring day. The asphalt shows temperatures that reach 61°F, compared to the temperature

of the concrete that decreases by almost 20°C. This demonstrates that under normal conditions, in a country like Puerto Rico where the solar radiation received

/seg) is given by the following relationship:

*<sup>C</sup>* (1)

), and *C* is specific

*Urban Heat Island Effects in Tropical Climate DOI: http://dx.doi.org/10.5772/intechopen.91253*

*Vortex Dynamics Theories and Applications*

*Net radiation urban vs. rural data (2009–2019).*

*Average annual wind speed - urban vs rural area.*

**Figure 10.**

**Figure 11.**

radiative losses from urban buildings and street materials keep the city's air warmer than that of rural areas. For this case, it is important to consider the location of the urban site and rural site. San Juan is located on the NE coast of the island of Puerto Rico. It is surrounded by waters of the Atlantic Ocean. The climate is tropical marine, slightly modified by insular influence when land breezes blow. San Juan is representative of most of the coastal localities on the island. That proximity to the

Buildings' volume, orientation, and the aspect ratio of the spaces between them affect the exposure of urban surfaces to the solar radiation. The concentration of concrete structures without green surfaces between them increases the air temperature of urban areas. In this case study, the concentration of buildings is significantly higher in San Juan than in Gurabo, Puerto Rico (see **Figure 12**). The gray plots indicate the building structures in each city. At a first glance, it is observed that there is a greater amount of building structures in the city of San Juan. The city of San Juan has three times more building structures than the city of Gurabo. The city

of the surface area of which 15.89 km2

are of building

of the surface area

coast makes wind speeds higher than in the rural area (see **Figure 11**).

structures. On the other hand, the city of Gurabo has 73.22 km2

are of buildings.

**188**

**5. Surfaces and materials**

of San Juan has 127.98 km2

of which 3.33 km2

**Figure 12.** *Building structures San Juan vs. Gurabo, Puerto Rico.*

The complex heat exchange between buildings' mass and adjacent air changes the intensity and patterns of airflow in urban canyons where wind patterns are also affected by the canyon-like structure of streetscapes surrounded by tall buildings. Urban surface materials' thermal characteristics (specific heat, mass, conductivity, and diffusivity), color, texture, and coverage alter heat exchange in urban settings and are important to determine UHI.

Some construction materials have properties that tend to exacerbate the heat island problem. Two material properties are important to heat storage: thermal conductivity and heat capacity. Materials with high thermal conductivity tend to conduct heat into their depths. Materials with high heat capacity can store more heat in their volume. A combination of these properties, called thermal diffusivity, is an important indicator of how easily heat can penetrate a material. Thermal diffusivity is calculated by dividing a material's thermal conductivity by its heat capacity. Rural areas tend to be composed of materials of lower thermal diffusivity, while urban areas have higher diffusivities. This enhances the storage of heat during the day and its slow release at night [12].

Thermal diffusivity (mm<sup>2</sup> /seg) is given by the following relationship:

$$\mathbf{or} = \frac{k}{\rho C} \tag{1}$$

where *k* is thermal conductivity (W/mK), *ρ* is density (kg/m3 ), and *C* is specific heat (J/kgK).

Another significant material characteristic is the albedo. Urban areas are considered with a low albedo, while rural areas are considered with higher albedos. Most urban materials reflect less incoming solar energy than materials commonly found in rural areas. **Figure 13** shows differences of temperature between two widely used materials in Puerto Rico, such as asphalt and concrete, at 14:00 hours on a spring day.

The asphalt shows temperatures that reach 61°F, compared to the temperature of the concrete that decreases by almost 20°C. This demonstrates that under normal conditions, in a country like Puerto Rico where the solar radiation received

**Figure 13.** *Asphalt (left) vs. concrete (right) temperatures (°C).*

throughout the year is constantly high, the roads built on asphalt should be changed to another material such as concrete, where heat emissions decrease considerably.

Commonly in urbanized places, two prominent materials have low values of solar reflectance: asphalt paving and built-up roofing (black roofs). The prevalent use of these materials lowers the overall solar reflectance of communities. Some of the characteristics of the materials commonly found in urban and rural areas are presented in **Table 1**, where the specific heat capacity and albedo are important features when reference is made to UHI.

In addition to the materials used in structures, road, and roofs, detailed computational and wind tunnel study shows that building packing density or how packed buildings are erected in a unit area also affects the movements of polluted and heated air from the pedestrians' levels, which eventually affects UHI. Reda et al. [13] performed computational fluid dynamics (CFD) simulations using OpenFOAM as well as ran experiments using blocks in wind tunnel using the Kuala Lumpur City Center, at five different locations representing different building densities. The results show that the more packed buildings are spaced, the harder for the incoming winds to clear the polluted and heated air trapped at low levels. Based on further details of the CFD simulations and atmosphericscaled measurements, there are complex interactions such as vortices and largescale features in the bulk movements of air and the more static air at near the grounds [14].

One of the characteristics of cities with UHI effects is the increase in impervious areas, where there is change in land use, i.e., grass or trees have been converted to parking lots and roads. These changes have increased flash floods in cities, leading


**191**

*Urban Heat Island Effects in Tropical Climate DOI: http://dx.doi.org/10.5772/intechopen.91253*

in the following topic.

**6. Flood alert system**

the flood in the area of the disaster.

methods to notify the affected person.

*Diagram of the process for a flood alert system.*

flooded areas in real time through a web service.

areas [16].

is possible.

**Figure 14.**

**7. Proposed system**

to major economic disasters and human losses. A personal flood alert system is being proposed as a mitigation method for this type of event, and these are shown

One of the effects of UHI is flash floods, which is a consequence of the increase of the impervious areas. Floods are the most frequent disaster type and cause more humanitarian needs than other natural disasters. The use of new technologies with higher accuracy, covering areas missed by radars, is important for flood warning system efforts and for studying and predicting atmospheric phenomena [15]. Almost 90% of all-natural disasters in the United States lead to flooding, and 20% of all flooding claims happen in low to moderate flood risk

This information is important when judging where to live. Home insurance does not cover anything that is not attached to the house. Insurance policies for cars, for example, that are the most affected by flooding since most of them are outside must have specific insurance called comprehensive insurance. This system not only can save a family's pocket and vehicle, but it can also save lives by notifying them of the flash flood occurring in the area. In addition, it can help gather information about

Many people lose their vehicles due to flash floods at parking lots. A way to avoid such disasters is by creating a flood alarm system that detects flood levels from their own cars making this alert more specific depending on individual cases. The system must be able to do the following: detect and measure water elevation considering the type of vehicle and its size. The alarm will function via phone call or text. As an alternative method, if there is no signal in the area, the cars' alarm system will alarm the owners instead of a phone call or text. Giving security to any of these two

How the system works is indicated in **Figure 14**. Once the system detects the sudden rise in water level, it will alert the owner through phone call or text. As a final step, the owner of the vehicle will move the car to a safer location if it

The proposed system alerts the client when the water level is a threat to the vehicle. This system includes a set of sensors that will perceive different measurements in water level and vehicle acceleration. If the water level increases to a threatening level, it will alert the client via web service through a text message which notifies about a sudden flood every 10 seconds. When for any reason there is no signal, the system has the option to send a notification so that the vehicle horn starts to go off; this functions as another alternative. In case that the car is in motion, it will notify the client by an audible notification. The collected data will be used to report

**Table 1.** *Material characteristics.* to major economic disasters and human losses. A personal flood alert system is being proposed as a mitigation method for this type of event, and these are shown in the following topic.
