نوع مقاله : مقاله مستخرج از رساله دکتری
1 دانشجوی دکترای جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل، ایران.
2 استاد جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل، ایران.
3 دکترای جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل، ایران.
عنوان مقاله [English]
In urban regions, thermal islands are exacerbated by the heat waves (HWS) effect, and it has the potential to negatively influence the health and welfare of urban residents. Scientists predict that heat waves will intensify and become more persistent in the coming years due to climate change. As a result, the likelihood of these two phenomena occurring simultaneously will increase in the coming years, even in small, non-industrial cities. Therefore, the purpose of this study is to compare the impact rate of thermal islands from the occurrence of heat waves in Kermanshah and Ilam cities from 2003 to 2018 and It is tried to determine under the conditions of heat waves, Which of the studied cities and at what time of the day the intensity of urban heat islands has increased?
In order to identify and extract heat waves, the maximum daily temperature data of Kermanshah and Iilam stations, from 2003 to 2018, by using Fumiaki Index and MATLAB software, days whit temperature above +2 standard deviation or above the mean Normalized Thermal Deviation (NTD) that lasted at least two days, were identified as the day with HWs and calculated by equation 1:
Where T (i, j, n) temperature of day i th from month j th in year n th, the average temperature of day i from month j. To eliminate the noise in the mean, a 9-day moving average filter was performed on these data three times and calculated by equation 2:
Where ∆T= (i, j, n) absolute deviation of temperature from the long-term average on day j th of the month i th, in year n th compared to the long-term average temperature of the same day. In order to the values of temperature deviation of different times and places to be comparable at a certain time and place, it is necessary to standardize these absolute values of temperature deviation by means of temperature diffraction. Like day-to-day changes, diffuse T∆ at 31 days for each day is calculated by equation 3, then the 9-day moving average was performed three times
The value is the average temperature deviation in 31 days that is calculated by equation 4:
Finally, Normalized Thermal Deviation (NTD) is calculated by the following equation:
Where .Then in MATLAB software, days with temperatures +2 above average (NTD) and lasting at least two days, were selected as the day with the HW (Equation 6).
Then the thermal island was calculated in Kermanshah and Iilam cities using Equation 7:
Where SUHI, is the surface heat island, MLSTurban is the average surface temperature in the urban area and FLSTrural is the surface temperature with the highest frequency of occurrence in the rural area.
Results and Discussion
The purpose of this study was Comparison the Impact rate of thermal islands from the occurrence of heat waves in Kermanshah and Ilam cities. Which has had an increasing trend in Kermanshah and no trend in Ilam. Also, the highest monthly frequency of heat waves in both cities was in March. Also the maximum duration of this risk was 4 days and short-term in Kermanshah and 6 days and long-term in Ilam. The results also showed that in both the heat wave and no heat wave condition, most of the day the cold island and at night sometimes the heat island (although weak) is formed in the Kermanshah and Ilam city centers, but in the heat wave conditions, especially in daytime and in Kermanshah city, the intensity of thermal islands was higher than normal. Studies also showed that the persistence of heat waves did not play a significant role in the intensification of thermal islands because the impact of thermal islands from the occurrence of two-day and four-day heat waves was almost the same. In the studied cities, in both Heat wave and no heat wave condition, a cold island has been formed in the city center, but in each heat wave, the intensity of the cold island has been more than a normal day for at least one day. In Ilam, even at night, mostly the cold islands have been created in the city center, although its intensity has been less compared to the daily cold islands. However, the most intense heat island in Kermanshah was in normal conditions, which was 3.5 degrees Celsius, but in Ilam, the most intense heat island occurred in heat wave conditions, which was 1.6 degrees Celsius. According to the explanations provided, the occurrence of heat waves did not have an effect on the intensification of thermal islands, especially during the day. In heat wave condition, in both cities the percentage of relative humidity was lower than normal, but the maximum wind speed in both cities was sometimes higher than normal days. to some extent indicates the open development horizons of the progress of the study area.
According to the results, thermal islands in both cities, especially in the daytime, even in the absence of heat waves in the center of the cities under study and have been affected by the occurrence of heat waves. Therefore, because according to scientists, climate change will increase climate risks such as heat waves, and the current small and non-industrial cities will experience more heat waves in the coming years, and will certainly grow and develop. Therefore, in order to prevent the negative consequences of the interaction of heat waves and heat islands in the future, further research is necessary. Also, in order to reduce the intensity of thermal islands and reduce the surface temperature in the center of these cities in the coming years, solutions such as: covering surfaces and buildings with materials with high heat capacity, protection of green spaces and creating green roofs, especially in urban centers, paying attention to the direction of the wind in the constructions so that there is a possibility of wind canalization and heat discharge between the buildings. Adjusting the density of buildings and their decentralized construction in the center of these cities seems necessary.