Urban Thermal Landscape Pattern Variation In Yinchuan City Based On Remote Sensing From1989to2011

With the process of urbanization, land use/cover types and pattern changes a lot, which alters the urban thermal environment and arouses a series of ecological problems. Studying the mechanism of urban thermal environment change in typical zones can reflect the distribution of urbanization intensity from the perspective of urban thermal environment, evaluate the impact of urbanization on ecology and environment, provide theoretical basis for measures of regulating and controlling urban heat island effect (UHI), and finally provide good references for ecological urban planning, environmental monitoring, and sustainable development of similar scale cities.Based on3LandsatETM+/TM images of Yinchuan from1989to2011, this paper retrieved land surface temperature (LST) by Qin’s mono-window algorithm. With exploratory spatial data analysis (ESDA) method and variograms, LST thermal pattern, spatial characteristic and spatial heterogeneity were analyzed. Moreover, by the theories and method of Landscape ecology, thermal landscape pattern and variation rule were studied, and impact of land use/covers on thermal environment were also analyzed, and finally some results were attained as follows:1. Thermal environment characteristics of study area:In recent20years, thermal environment alters a lot, and high-LST area consist of built land and bare land. As urban area expands, high-LST area of urban area enlarges. LST distribution has positive spatial autocorrelation, namely, with the change of land use/covers, high-LST area and low-LST area have spatial aggregation in distribution, and LST distribution has good spatial dependence.2. Thermal landscape pattern:Cool island and weak heat island patches account for large area in study area, which shows ecology and environment in study area are well. In recent20years, cool island area decreased and urban heat island area increased. High-grade thermal patches area was maximum in1989, had a little area reduction, and increased in2011; Urban heat island area in all urban areas are expanding, but there exist low-grade thermal patches in main urban areas, which improve the ecology and environment in main urban areas.3. Thermal landscape pattern variation:At class level, all thermal patch types mainly tended to be more fragmented from1989to2000, more aggregated from2000to2011, and patches shape tended to be simplified; At landscape level, urban thermal landscape pattern saw a turning point in2000:urban thermal landscape pattern was more fragmented from1989to2000, but, it became more aggregated and patches shape tended to be simplified from2000to2011. Each grade of urban thermal patch types became even-distributed. These changes indicate the increase of human activities intensity.4. Thermal patches transition:Under the influence of human intervention, cool island consisting of green land and waterbody was the stablest urban thermal patches. The low-grade thermal patches (cool island and weak heat island) were easy to transfer among themselves, but they were difficult to transfer to high-grade thermal patches. Moderate heat island was easy to transfer to the low-grade thermal patches or higher-level thermal patches. The high-grade thermal patches (strong heat island and Strongest heat island) were easy to transfer among themselves, but they were difficult to transfer to low-grade thermal patches.5. Relationship between LST and land use/cover types:Average LST of bare land is highest, and average LST of green land and waterbody are lower. Bare land and built land contribute much to the formation of high-grade thermal patches, hence, they are main contributor to urban heat island intensity. Green land and built land with cooling effect have actual significance on segmenting and controlling urban heat island distribution, therefore, rational planning of green land and waterbody pattern conduce to improve urban thermal environment.6. Relationship between LST and land use/covers pattern:At the landscape level, LST and landscape metrics have little significant correlation. Compared with landscape level, at the class level, correlation between LST and landcape metrics is more significant, which indcates different land use/covers patterns have different impact on LST. Hence, pattern of the same land use/cover influence LST more.7. Under the certain scale and radiation background, through building regression model, the effect degree of land use/cover types and pattern on LST were analyzed quantitatively. Given the same hypothesis, the results showed:in recent20years, the average LST in main urban areas increased by16.89%.