Method

Hot and dry extreme events are detected using ECMWF climate reanalysis (ERA5) hourly data (see limitations). Hot conditions are assessed through daily maximum 2m temperature (Tmax). Dry conditions are assessed through daily differences between total precipitation and evapotranspiration averaged over the preceding 30, 90 and 180 days (PEI_30, PEI_90, PEI_180). Conditions at a specific location (spatial grid cell) are considered extreme when Tmax is greater than the 99th percentile and a drought indicator is less than the 1st percentile of their respective distributions over time for that specific spatial grid cell. These Discrete Extreme Occurrences (DEO) are stored in the EventCube. Through a connected component analysis, connected DEOs are assigned unique labels when they are contiguous in space or time. These labels are stored in the labelcube. Summary statistcs for all uniquely labelled extreme events are stored in table EventStats. 

For a graphical overview of the method, see the workflow.

Limitations

• Heatwaves are computed from daily maximum temperature only.
• Compound hot and dry conditions are assessed from the univariate temporal distribution of temperature and drought indicators. Multivariate distributions are not considered.

Limitations of Dheed 2.0

• At the time of computation, only ERA5 preliminary back-extension from 1950 to 1978 was available.
• There is no minumum duration set for heatwaves.
• Labelled events are computed from 2016 to 2021.