Temperature Variation with Height The temperature values obtained on different

elevations within different time intervals are shown in the Figure 8. From the figure, it’s clearly evident that generally up to 9 m from ground the temperature is decreasing and from there the temperature is increasing with height. But at the height of 27 m the temperature reduces than the temperature at the height of 25m except in the time interval from 1.00 pm to 3.00 pm.

Figure 8 - Temperature Variation with Height at Different Time Intervals

The Reduction in the temperature up to 9 m could be due to the reduction of the effect of the

heated road in the canyon. The reflective radiations from road warm up the air up to a 9m from ground.

Figure 9 shows the temperature variation with height form 1.00 pm to 3.00 pm. From the Figure 10, it’s clear that the maximum solar radiation occurs at 1.00 pm. With that it can be stated that the maximum temperature should be occurred after 1.00pm. From Figure 9, it’s clear that within this selected time interval the temperature is increasing after 9 m from ground. It’s clear at 27 m the air temperature reaches to its highest within the time interval of 1.00 to 3.00 pm and that is at 2.15 pm.

Figure 9 -- Temperature Variation with Height at Selected Time Intervals

4.2 Ambient Air Temperature Reduction

with Implementation of Green Roofs

Figure 10 - Comparison of Temperature Variation with Radiation Flux

Temperature of the air varies with the solar radiation magnitude. According to the Figure 10, the maximum solar flux occurs at 12.00 pm and the maximum air temperatures take place at 1.00 pm. It can be clearly stated that the maximum temperature of the canyon air occurs just after one hour from the maximum solar radiation taking place.

Figure 11 - Temperature Variation of the City Compared to the Rural Area Air Temperature

The magnitude of the canyon air temperature varies with time. From the Figure 11, it’s evident that the air temperature is comparatively high in the city canopy in the case 1 than the normal air temperature. There, the case 1 represent the air temperatures of the canyon under the prevailing conditions of the city and case 2 represent the canyon air temperatures when all the flat slabs in the area are replaced with green roofs. This value is maximized at 1.00 pm. The canyon air temperature in that hour is 34.47°C where the normal air temperature (ambient air temperature) is only 31.3°C and the difference is more than 3°C. This is a further evidence of prevalence of heat island effect, in the compacted cities.

Figure 12 - The Temperature Variation with Time in Two Cases

The air temperatures obtained for each case in considered time period are shown in the Figure 12. The considered time period was from morning 7.00 am to evening 5.0 pm because the net all wave radiation is positive only in that period.

According to the Figure 12, the temperatures of the canyon air is high under the prevailing condition compared to that the flat slabs replaced with green roofs. When the flat slabs are replaced with green roofs the canyon air

temperatures reduces approximately by 1.5 °C than the prevailing condition. This reduction of the temperature can be seen throughout the considered time period.

5. Conclusion

Due to the impervious faces the city temperature is increased compared to the temperature in rural areas. Green roofs are identified as a solution for the above mentioned problem.

Canyon temperature is increasing with height after 9 m from ground during 1.00 pm - 3.00pm. When all the flat slabs are replaced with green roofs it can be stated that this increasing canyon air temperature can be reduced by 1.5°C. This reduction can be maintained throughout the day time with implementation of green roofs on existing flat roof slabs. The findings are very important when considered the future development to be made. If the future constructed buildings are coupled with green roofs, the temperature issues that would have aroused due to impervious surfaces can be reduced. Other than the temperature benefits the visual benefits are also there with the increased greenery in the city.

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