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Explanation of Weekly Report on Global Climate Events


Extreme Climate Events

    In general, extreme climate events are those that people rarely experience. They include various time ranges of phenomena such as heavy storms, heat waves and droughts, and often cause weather-related disasters and influence socioeconomic activities. In statistical terms, JMA defines an extreme climate event as a phenomenon that would happen once every 30 years or less.

Identification of extreme climate events

    The report is produced mainly from SYNOP messages received via GTS from National Meteorological Services around the world. Extreme climate events are identified as outlined below.

1. Weekly mean temperature and weekly total precipitation for each observatory around the world are calculated from SYNOP messages. Details of calculation are described on the 'Explanation of Weekly Mean Temperature and Total Precipitation' page.

2. Extreme climate events are then identified using the criteria described below.

    Normal values, standard deviations and thresholds of quintiles for monthly mean temperature and monthly precipitation are based on data from 1981 - 2010. In the following criteria, 30-day normal values, standard deviations and thresholds of quintiles are used. These are calculated by interpolating monthly values for the previous and current month, or for the current and the following month

a. Warm/Cold (extremely high/low temperature):
    The positive/negative anomaly of weekly mean temperature exceeds three times the 30-day standard deviation.
b. Wet (extremely high precipitation):
    Precipitation in a week exceeds a threshold decided on the basis of the 30-day precipitation normal. If this normal is 10 mm / 100 mm / 200 mm / 500 mm, the threshold is 153% / 98% / 81% / 59% of the normal value. If the normal of the 30-day precipitation exceeds 500 mm, the threshold is fixed at 59%.
c. Dry (extremely low precipitation):
    Precipitation in the last 30-day is less than the threshold of quintile 1 for the 30-day period.

Figure of Global Extreme Climate Events

    The figure indicates areas where extreme climate events are identified from SYNOP messages, weather-related disasters reported from official media sources and tracks of damage-causing tropical cyclones based on preliminary data from worldwide Tropical Cyclone Centers.

Note: Figures and documents of the weekly reports by 10 May 2011 are based on climatological normals which calculated on 1971-2000.

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