IAC News

International Symposium on Extreme Precipitation and Extreme Flooding
held by the Committee on Hydroscience and Hydraulic Engineering”

After the transition to the new Corona 5 class, JSCE held its first international event using both in-person and remote methods. The event was organized by the Committee on Hydroscience and Hydraulic Engineering with the invitation of M.L. Kavvas, Distinguished Processor, University of California, Davis, who has been working for many years on estimating realistic extreme precipitation and extreme flooding for structural design in the wake of a series of flood damage caused by extreme rainfall events around the world. The symposium was held as follows.

An outline of the International Symposium is as follows:

1. Background (10 minutes), Toshio Koike (Director, International Center for Water Hazard and Risk Management, Public Works Research Institute)

After a series of floods and new policies that have occurred every year since 2013, the government is promoting “River Basin Disaster Resilience and Sustainability by All,” which is implemented by all parties involved. He explained that Japan has initiated river planning that takes climate change into account, but has yet to reflect extreme phenomena in its planning, showing images of the movement and development of heavy rain fields from the 2015 Kanto and Tohoku torrential rains and the 2016 typhoon rainfall.

2. Keynote Speech (90 minutes) “Recent Advances in Physics-Based Numerical Modeling Approaches to Estimate Extreme Rainfall and Extreme Flooding (PMP/PMF)” M.L. Kavvas, Distinguished Professor, University of California, Davis; Yoshihiko Izeri, Hydrology Laboratory, UC Davis Manager.

The conventional method of estimating maximum possible precipitation was reviewed. Next, the authors discussed two cases: an atmospheric river on the West Coast (a winter weather phenomenon in which moist air from the vicinity of Hawaii flows to the West Coast and brings heavy rainfall) and hurricane rainfall on the East Coast. The method maximizes rainfall and flood flow in two steps by optimizing the shift of atmospheric boundaries and relative humidity. The method was then applied to climate change scenarios to show changes in the frequency of rainfall.

3. Panel Discussion (50 minutes): In addition to Kavvas and Koike, Eiichi Nakakita (moderator, Director and Professor of Disaster Prevention Research Institute, Kyoto University) and Tadashi Yamada (Distinguished Professor of Chuo University) discussed PMP/PMF from the three perspectives of importance, reliability, and future prospects, and offered the following opinions.

• Level 2 in climate change adaptation measures corresponds to PMP/PMF.
• It is important to statistically demonstrate confidence intervals in the forecast.
• Almost all of Professor Kavvas' education in hydrology at a U.S. university in the 1970s was in statistics, while at another he studied the physics of water. Later, he studied atmospheric science collaboratively and was able to develop hydro-meteorological models and estimate physical upper limits.
• There are many in the U.S. who believe that statistical methods can be used to estimate the upper limit, but this is not possible.
• Estimates of precipitation during historical floods that occurred prior to the start of observations yielded results that did not necessarily indicate heavy rainfall.
• Some areas show a 10-year cycle of heavy or light rainfall, while others do not. The ocean is the key.
• If the PMP/PMF is clarified, it will have implications for “River Basin Disaster Resilience and Sustainability by All.”
• The characteristics of the statistical approach can be understood by reproducing ensembles of past events.

Many of the webinar participants listened to the webinar with simultaneous interpretation and commented that they were able to listen to a lecture by a world-leading scientist that they cannot experience without such a special arrangement, that they thought this was a top priority global issue, that they could understand the difference between statistical and physical approaches from the keynote speech and discussions, and that they could understand the general framework of the topic because of the background explanation, even though it was not their specialty. On the other hand, some participants pointed out that the time delay of the simultaneous interpretation bothered understanding, that they could not understand the translation of technical terms, and that there were times when audio did not come through to the microphone.
 

International Symposium officials and audience participants

Panel discussion (from left to right: Eiichi Nakakita, Toshio Koike, Tadashi Yamada, M.L. Kavvas)

【Reported by Junichi Yoshitani, Working Secretary for Organizing International Symposium, Committee on
Hyroscoence and Hydraulic Engineering (Professor, Shinshu University)】