A joint work by Prof. Taisuke BOKU in Division of High Performance Computing Systems, and Prof. Hiroyuki KUSAKA and Researcher Dr. Takuto SATO in Division of Global Environmental Science, was published at 2021 International Conference on Network and Parallel Computing (IFIP NPC2021, held in Paris on November 2021) and awarded to one of the best papers in the conference. This work improves the performance of City-LES simulation code for detailed urban region atmosphere simulation developed in CCS, and ported to full GPU-version under collaboration of codesigning by two research divisions, achieving up to 17 times faster computing performance than CPU-version on Cygnus supercomputer.