**3. Study locations**

*Vortex Dynamics Theories and Applications*

extent via increased convection [3].

ered the dry season with 2.32 inches.

*San Juan, Puerto Rico, annual temperature (°F) pattern for 2000–2019.*

**2. Local climate**

precipitation has also increased by a factor of two [2].

surrounding rural areas better regulate surface temperatures.

illustrated that the average mainland US temperature has increased by 1.1°C (2°F) since about 1960, precipitation has increased by 5%, and the frequency of heavy

Another important aspect to be studied is evapotranspiration (ET) because the increase of impervious surfaces prevents the movement of air and water which are key in the cooling processes of evaporation and transpiration and creates a typical "heat urban islands" of warmer temperatures, while the green vegetation in the

This could be evident with the analysis between cities such as San Juan, Puerto Rico (urban), and Gurabo, Puerto Rico (rural). A decrease of evapotranspiration energy from the rural area to the suburbs and finally to the urban area is expected. This change will coincide with a decrease in vegetation coverage. Without the immediately available energy outlet of evaporation, urban and suburban areas must store more energy during the day. The stored energy is subsequently released to the atmosphere at night, primarily through higher radiant emissions and to a lesser

The flash flood is a consequence of an urban heat island effects. Most people consider that sudden floods are the product of weather phenomena such as tropical waves through even hurricanes. Previous studies have shown that most of flash floods are caused by anthropogenic behavior generally named anthropogenic heat, which is generated by human activity and comes from many sources, such as buildings, industrial processes, and change in land use from pervious to impervious.

The climate of the Caribbean is characterized as subtropical with relatively dry winters and wet summers [4]. The dominant large-scale atmospheric influence on the climate is the North Atlantic subtropical high (NAH). The average temperature at the San Juan, Puerto Rico, station last year was 80.74°F. **Figure 1** shows the annual temperature between the years 2000 and 2018 for the months of January and September [5]. On the other hand, the amount of rainfall varies considerably throughout the study area. Most of the rainfall occurs during the month of August with 7.15 inches on average for the last 20 years. The month of February is consid-

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**Figure 1.**

The study UHI is based on the premise that significantly warmer surface temperatures exist in urban settings as opposed to their surrounding rural areas. To make sure that this premise is correct for the Puerto Rico case, seven locations have been selected, which cover the island (see **Figure 2**).

The research began with the use of historical temperature data taken from the southeast regional climate center webpage. The website has the advantage of having historical data such as temperature and precipitation of at least 50 years. For this research, the temperature was the parameter for defining the problem. Data with more than five decades were used to study the changes in temperature between the urban area and the rural area.

The city of San Juan, Puerto Rico (18.44, −66, geographic coordinates in decimal degrees latitude and longitude), is designated as an urban area, and it is the capital city of Puerto Rico. The number of residents in the city is declining from 428,800 in 1957 to 321,000 in 2019. The city designated as a rural area is Gurabo, Puerto Rico (18.25, −66, geographic coordinates in decimal degrees latitude and longitude), located at 20 km from San Juan, Puerto Rico. In 1957 it was estimated that it had 16,600 inhabitants, and in 2019 it has 46,000 residents [6].

**Figure 3** shows the difference in temperature between urban and rural areas. The data was taken from 1957 to 1967 at each station and displays a difference in temperature on average of 2.62°F. Furthermore, the same comparative analysis was carried out for the years between 2008 and 2018 (see **Figure 4**). For this case, the difference between temperature increases was around 3.46°F.

Stations located in San Juan, Puerto Rico, and Gurabo, Puerto Rico, show that both period 1957–1967 and period 2008–2018 temperatures are on the rise in heavily urbanized areas where there is a conversion of natural vegetation to urban dwellings.

A NASA study found that in the summer months, the temperature in New York was on average 4°C higher than in the surrounding area. Studies from the 1960s already pointed to the phenomenon of heat island, but the effect is becoming more intense due to climate change.

Another way to verify the existence of heat islands is to make a parallel analysis of urban area temperature behavior as it moves away from its center and approaches a rural area. As shown in **Figure 5**, the first station away from the urban location is

**Figure 2.** *Study locations, Puerto Rico.*

**Figure 4.** *The difference of temperature (°F) between urban and rural areas (2008–2018).*

Rio Piedras, located at 6 km; the next station is Trujillo Alto, located at 12 km from San Juan, Puerto Rico; and the last is Gurabo, Puerto Rico, considered as a rural area located at 20 km from San Juan, Puerto Rico.

Considering the temperature average during the last 55 years in the urban area (San Juan, Puerto Rico) for all months, this shows the highest values compared to the other stations, during the 12 months of the year. It is observed that the coldest months during the period studied are the months of January and February and those with the highest temperatures are August and September. The latter matches with the peak of the hurricane season, where the temperature on the surface of the Atlantic Ocean is at its highest and optimum level for the formation of more powerful hurricanes (see **Figure 6**).

Stations located in San Juan, Puerto Rico, show that both January (minimum) and September (maximum) are on the rise in heavily urbanized areas where there is a conversion of natural vegetation to urban dwellings. This theory was before validated by Gonzalez and Comarazamy in 2009 [7]. Urban data analysis also found

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**Figure 7.**

**Figure 5.**

**Figure 6.**

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

warming in the San Juan, Puerto Rico area, with a trend of 0.09%/year. from 1957 to 2012. This result was obtained when estimating the delta of change of all the months of the year from 1957 to 2012. **Figure 7** shows the projection for the warmer month (September). Using the 0.09% growth (obtained from 1957 to 2012) and the recent data (2000–2019), it is observed that, although there is a difference in some

years, after each decade this projection must be more accurate.

*San Juan data station (°F) and projection data with 0.09% increase yearly.*

*Average temperature (°F) using data of 55 years in four different stations.*

*Location of stations: San Juan, Rio Piedras, Trujillo Alto, and Gurabo, Puerto Rico.*

#### **Figure 5.**

*Vortex Dynamics Theories and Applications*

Rio Piedras, located at 6 km; the next station is Trujillo Alto, located at 12 km from San Juan, Puerto Rico; and the last is Gurabo, Puerto Rico, considered as a rural area

Considering the temperature average during the last 55 years in the urban area (San Juan, Puerto Rico) for all months, this shows the highest values compared to the other stations, during the 12 months of the year. It is observed that the coldest months during the period studied are the months of January and February and those with the highest temperatures are August and September. The latter matches with the peak of the hurricane season, where the temperature on the surface of the Atlantic Ocean is at its highest and optimum level for the formation of more power-

Stations located in San Juan, Puerto Rico, show that both January (minimum) and September (maximum) are on the rise in heavily urbanized areas where there is a conversion of natural vegetation to urban dwellings. This theory was before validated by Gonzalez and Comarazamy in 2009 [7]. Urban data analysis also found

located at 20 km from San Juan, Puerto Rico.

*The difference of temperature (°F) between urban and rural areas (2008–2018).*

*Difference of temperature (°F) between urban and rural areas (1957–1967).*

ful hurricanes (see **Figure 6**).

**184**

**Figure 3.**

**Figure 4.**

*Location of stations: San Juan, Rio Piedras, Trujillo Alto, and Gurabo, Puerto Rico.*

#### **Figure 6.**

warming in the San Juan, Puerto Rico area, with a trend of 0.09%/year. from 1957 to 2012. This result was obtained when estimating the delta of change of all the months of the year from 1957 to 2012. **Figure 7** shows the projection for the warmer month (September). Using the 0.09% growth (obtained from 1957 to 2012) and the recent data (2000–2019), it is observed that, although there is a difference in some years, after each decade this projection must be more accurate.

**Figure 7.** *San Juan data station (°F) and projection data with 0.09% increase yearly.*

*Average temperature (°F) using data of 55 years in four different stations.*

Rosenzweig et al. [8] analyzed the New York city heat island effect model by taking six case study areas and tested the mitigation strategies. They found that vegetation helps to keep surfaces cool more effectively than increasing the albedo. But they suggested that in order to reduce the temperature in New York city, replacement of low-albedo materials with high-albedo light-colored materials will work great as 64% of the surface area of the city can be replaced easily.

Sailor [9] describes that the urban heat island effect mitigation can be done in two ways. One is by increasing the albedo of the urban surface, and the other is by increasing evapotranspiration. On the other hand, white materials which have albedo greater than 0.60 instead of black materials having albedo of 0.05–0.10 can be used as roofing materials. They found that the roof temperature dropped by 25**°**C for 0.60 albedo compared to that of 0.20 albedo. More solar radiation could be reflected if the road and highway pavements were of high-albedo materials. White cement mixtures can be made for which the albedo should be higher than the most reflective gray cement mixtures. However, use of high-albedo materials for roads and highway pavement may not be so much effective because of the sky view factor. Even if, it is used, some of the reflection will be intercepted by the buildings surrounding it.
