| dc.description.abstract | According to the observation data, the warming is significant over the latest 30 years in Taiwan. Despite of the large scale weather system changed, the changes in land use/land cover characteristics will affect the surface-atmosphere energy budget, and impact on the weather system. In this study, we try to understand the global climate change effect and the local land use change effect on regional climate change over the latest 20 years in Taiwan. The Weather Research and Foresting (WRF) model was applied to simulate the spring (April) and the autumn (October) in 1990-1992 and 2010-2012. To emphasize the human activity affects to the environment, we update the land use data which is derived from the MODIS satellite products. In part one, we analysis the large scale climate change in Asia, and do statistics the observation data in Taiwan over the past 20 years. In part two, we focus on the land use effect under the same model setting in the long term simulation by WRF model on 2010-2012. In part two, we discuss the effect of lands use change on climate in the Taiwan area is important or not. The simulation periods are 1990-1992 and 2010-2012.
Since the long term land use observation data is limited, we use the USGS data from the WRF model as the 1990s’ land use, and we reprocess the land use data from the MODIS satellite as the 2000s’ and 2010s’ land use (the MODIS2001 and the MODIS2010) to update land use in Asia. The new land use data from MODIS is more realistic and can represent the truth land use in recent Taiwan. There are only little difference between MODIS2001 and MODIS 2011. In the spring simulation set, the CRM area change from irrigated land to forest by MODIS data, which is more realistic than the old one.
The WRF model have the high wind speed error. The wind speed correction technique by Jiménez and Dudhia(2012) is used ,which can reduce the bias and RMSE of the wind speed.
Using two different land use data set to simulate the Oct, 2010-2012, the wind speed in MODIS2011 is much closer to the observation data. The characteristic of diurnal cycles are also difference. The update land use can change the energy budget, and then modify the planetary boundary layer height. The updated land use can make the temperature higher and wind speed lower in the daytime over the western part of Taiwan. In the nighttime, the urban island effect is obvious in the urban area. Therefore, the land use data change is really important form the long-term climate simulation.
By the historic observation data, it is much warmer in the October. The wind speed is increasing in the North-East area of Taiwan. The rainfall also increased in October. In April, the temperature is decreasing and the wind speed is increasing in the North-East area of Taiwan, but the other part of Taiwan have the opposite behavior. The rainfall is increasing in April, which is different from October.
The simulation results in spring and autumn over the past 20 years in Taiwan exhibits as below. In October, the tendency of climate change are: weaker Siberia High, stronger south-west wind (weaker north-east wind). In April, the easterly wind component is increased in the eastern coastal of Taiwan. The rainfall increases in the eastern Taiwan (windward side), and decrease in the west part (leeside). The temperature increases all over Taiwan in October, but increase in the east part and decrease in the west part in April. Most of the change tendencies are the same as the observation.
Both contributions of climate change and land use change on the regional meteorological fields cannot be ignored over the past 20 years in Taiwan. The correct land use data is important for the regional weather research model, especially for the climate issue. | en_US |