Analysis Of Characteristic About Urban Heat Island Effect In Changsha

Nowadays, research on Urban Heat Island (UHI) effects plays an important role in the urban ecological environment development, city landscaping and planning, energy usage, and resident livings, etc. After the "Reforms and Opening up", Changsha has been experiencing a rapid urbanization process. The combination of both human and natural factors makes UHI in Changsha very prominent. This requires a systematic analysis on the UHI characteristics.This study mainly includes:1. Analyze the temperature change pattern (interdecadally, yearly, seasonally, monthly, and daily) for both urban and suburban areas based on4national meteorological stations observed data (between year1971and2010, daily average/high/low temperatures) and200local automatic weather stations (AWS) observed data.The results show that i) The UHI in Changsha is not so obvious during1970s and1980s, and the interdecadal temperature is below the average of the last40years for both urban and suburban areas. Since1990s, all the temperature data showed a significant increase, especially after year2000. Comparing to1991-2000, the temperatures for2001-2010were increased by about0.9℃,0.8℃, and0.8℃for the average, average high and average low respectively for the urban areas. During the same period (2000-2010), UHI became more and more significant.ii)all seasons showed some sudden increase phenomenon for the interdecadal temperature changes. For the winter, all temperatures (average, high, low) showed sudden increases in the1990s:average temperature was increased by1.1℃for both urban and suburb; average high temperature was increased by1.3℃for urban and1.2℃suburb; average low temperature was increased by0.8℃for urban and0.9℃suburb. For spring, summer and autumn, the sudden increase occurred in the2000s, about one decade lagged. All temperatures (average, high, low) were increased by about1.0℃on average interdecadally. Among them, the average high temperature for spring was increased the most by1.6℃interdecadally.2. Perform UHI characteristic analysis for Changsha based on the average data from multiple selected representative stations located in both urban and suburban areas. The results show that i) Changsha exhibited UHI effect all year around; nighttime was larger than daytime and the largest occurred around the midnight. For some noontime,"Cold Island" effects existed when the urban is cooler than the surround suburban. The maximum hourly temperature difference reached10.5℃between urban and suburb areas.ii) UHI in Changsha has been intensified for all seasons:summer increased most (0.136℃/10a), then autumn (0.125℃/10a), and then spring (0.114℃/10a) and winter (0.086℃/10a).3. Perform systematic analysis on the UHI intensity tendency rate and UHI contribution rate to the temperature increase using three types of temperature tendency rate for both urban and suburban areas. The results show that i) For the rate of temperature increase, the trends are "Urban> Suburb","Average High> Average> Average Low". For the last40years, the rates of temperature increase for urban area are0.392℃,0.445℃, and0.376℃per decade for annual average, average high and average low, respectively. Those temperature increases mainly occurred during the last20years (1991-2010). The rates of temperature increase for urban area are0.820℃,0.794℃, and0.879℃per decade for annual average, average high and average low, respectively. Among all the rates, the most prominent is the average low temperature and the least prominent is the average high temperature, both are for urban area.ii) As to the seasonal rate of temperature increase, for the last40years, the trends are "Spring> Winter> Autumn> Summer" for average temperature,"Spring> Autumn> Winter> Summer" for average high temperature, and "Winter> Spring> Autumn> Summer" for average low temperature.iii) The UHI intensity tendency rates are0.108℃/10a,0.140℃/10a, and0.118℃/10a for annual average, average high and average low temperatures, respectively; and the corresponding contribution rates of UHI to the urban temperature increase are27.6%,31.5%and31.4%. Among all seasons, summer is the most and winter is the least.4. Analyze the relationship between UHI and urbanization process related data for Changsha. The results show that There is a good linear relationship between UHI intensity and urban population for Changsha, and a logarithmic relationship between UHI intensity and regional GDP, gross industrial production, and gross construction production.