Hybrid Downscaling Model for the High Resolution Urban Ueat Island Effects with the Global Warming

Abstract The combination of the urban heat island effects and the global climate change will give the prominent temperature change with a significant impact on the great number of people live in the big cities. For the adaptation to the climate change, optimization of population distribution, maintain or expanding green spaces and improvement of urban structure are studying. Since the intensity of the urban heat island may change with the global climate change, downscaling of the projections by the global climate models are necessary for the assessment of the effectiveness of the measures.

A very high resolution urban climate model should be necessary to estimate the effects of the modification of the urban structure. On the other hand, long-term downscaling are required for the estimation of the regional climate change. More than ten-year simulation with the horizontal resolution of less than 100m are very difficult by the current computers.

We propose a new way, hybrid downscaling method, i.e., the combination of a nested numerical mesoscal musicale climate model with coarse grid system (20km and 5km) and an analytical model for the higher resolution distribution of temperatures. We adopted WRF for the former. The letter is a analytical model fully using the atmospheric conditions and other variables estimated by the numerical models.

The estimation of the temperature distributions around the boundary between an urban area and a green area are compared with the observations during summer. Estimation by Hybrid model agree well to the observation, although the accuracy somewhat drop in the evening.

Acknowledgments. This study was supported by the Research Program on Climate Change Adaptation (RECCA) Fund by Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan and the Global Environment Research Fund (S-8) of the Ministry of the Environment of Japan.