TOKYO -- A new "heatstroke precautionary alert" warning system to notify the public when temperatures are becoming dangerously high will be tested from July 1 in nine prefectures in the Kanto-Koshin region, including Tokyo, according to a June 16 announcement by the Ministry of the Environment and the Japan Meteorological Agency (JMA).
The system will use a "heat index" based on factors including the temperature and humidity to measure conditions. In the event that the heat index is expected to exceed 33 degrees Celsius, a warning will be issued on a prefectural basis the day before the conditions are expected to occur. Testing is to continue until Oct. 28. The system will be subject to review from autumn, with an intention to roll it out nationwide for full use in the next fiscal year.
Heat index data will be measured in the nine prefectures from 120 locations, and in the event that just one of the observation points takes a measurement of 33 C, the alert will be issued in its corresponding prefecture. Those alerts will be conveyed via the JMA's disaster prevention information system, with affected municipalities and other bodies getting updates twice a day, one at 5 p.m. on the day before the expected high temperatures, and again on 5 a.m. on the day itself. A heat index reading of "33 C or more" is reportedly equivalent to an actual temperature of 35 C or higher.
In addition to measuring temperature and humidity, when formulating its readings the heat index also takes into consideration radiant heat from road surfaces and the walls of buildings, among other factors, giving it results with greater accuracy. In 2019, there were 20 days in Tokyo where conditions would have fulfilled the criteria to issue an alert.
The extreme high temperature forecasts service currently run by the JMA and announced by prefecture when temperatures are forecast to reach 35 C or higher, is expected to be retired within this fiscal year.
(Japanese original by Toshiyuki Suzuki, Science & Environment News Department)