Number of heat wave days during August 2003, as calculated using the Warm Spell Duration Index (WSDI). Calculated from daily temperature data, using ECA&D data of station-based indices. These indices were used to produce gridded fields of WSDI by averaging together the available station index values within each 2x2 degree grid cell. To classify as a heat wave there needs to be at least 6 days in a row above the 90th percentile for that day. The reason the maps show values below 6 is that there may be more than one station in a 2 degree grid resolution. If only one of these has a 6 day heat wave, the average of all stations will be less than 6. It is also possible that fewer than 6 days of a heat wave fell in the month of interest.

Number of heat wave days during July 2010, as calculated using the Warm Spell Duration Index (WSDI). Calculated from daily temperature data, using ECA&D data of station-based indices. These indices were used to produce gridded fields of WSDI by averaging together the available station index values within each 2x2 degree grid cell. To classify as a heat wave there needs to be at least 6 days in a row above the 90th percentile for that day. The reason the maps show values below 6 is that there may be more than one station in a 2 degree grid resolution. If only one of these has a 6 day heat wave, the average of all stations will be less than 6. It is also possible that fewer than 6 days of a heat wave fell in the month of interest.

Number of heat wave days during August 2002, as calculated using the Warm Spell Duration Index (WSDI). Calculated from daily temperature data, using ECA&D data of station-based indices. These indices were used to produce gridded fields of WSDI by averaging together the available station index values within each 2x2 degree grid cell. To classify as a heat wave there needs to be at least 6 days in a row above the 90th percentile for that day. The reason the maps show values below 6 is that there may be more than one station in a 2 degree grid resolution. If only one of these has a 6 day heat wave, the average of all stations will be less than 6. It is also possible that fewer than 6 days of a heat wave fell in the month of interest.

Number of heat wave days during August 1976, as calculated using the Warm Spell Duration Index (WSDI). Calculated from daily temperature data, using ECA&D data of station-based indices. These indices were used to produce gridded fields of WSDI by averaging together the available station index values within each 2x2 degree grid cell. To classify as a heat wave there needs to be at least 6 days in a row above the 90th percentile for that day. The reason the maps show values below 6 is that there may be more than one station in a 2 degree grid resolution. If only one of these has a 6 day heat wave, the average of all stations will be less than 6. It is also possible that fewer than 6 days of a heat wave fell in the month of interest.