Cooling effect range assessment of paddy fields in urban neighborhood by Landsat thermal imagery

Rice is the staple and vital food crop for the people in Asia and is also the major production crop in Taiwan. The paddy irrigated mainly by flooding the field, which consumes more water than the other crops. The planting cycle of paddy in general includes four periods: pounding, growth, strain of corn and after reap. Two of the four cycles, pounding and growth, must be irrigated in order for the paddy to grow up. Because of the irrigation water, the heat in air and land can be significantly absorbed, produce lower temperature in ambient of paddy, that is called the cooling effect. The cooling effect of paddy field is more significant in the urban neighborhood and can be one of the nature solutions to the global warming. There were few studies of the cooling effect of paddy field since it is difficult to get the temperature around the paddy field in large area. As the development of remote sensing technology, remotely sensed data have the attribute of instantaneous and wide range of views. Remote sensing data can be used more extensively and save more time and labor compare to the traditional measurement. This study utilized the thermal bands of Landsat-7 satellite dated from 2005 to 2010 and match with the different planting cycle of paddy, to analyze and estimate the range of cooling effect. The study area located in Taoyuan, where paddy fields were next to metro areas, providing environment to analyze and estimate the influence distance of the cooling effect. Land surface temperatures (LST) were derived from the thermal and optical bands of the Landsat-7. The LST in each of the buffer areas from the center line of paddy and metro area were estimated and the turning point at the LST-distance curve was considered the affected range of the phenomenon. Results indicated that the average range of cooling effects were 110, 90, 105and 80 meters for active growth, transplant seedling, and after harvested periods, respectively. It indicated that the lands covered with water are more effective to cool the temperature in residential areas.