...
- Climate generation dates:
- In the sub-seasonal, climate files are produced for each reforecast run date, so in total 8 (days per month)*12-1 = 95 dates in a calendar year with 1/5/9/13/17/21/25/29 of each month, excluding 29 February. The sub-seasonal climate files are generated continuously in a real time manner, right after the hydrological reforecasts are produced.
- The seasonal climatology is produced only once for each month of the year (so 12 sets).
- Climate lead times:
- In the sub-seasonal, for each of these climate dates, one climate file per daily lead time of the 46-day sub-seasonal range if produced. Here, all possible 7-day lead times, starting from days1-7, then days2-8, ..., out to days 40-46 (40 possible lead times) are considered. This way, the weekly mean climatology for all possible lead times will be available, and so for each real time forecast the right climatology can be used, with the correct lead time in days, depending on which day of the week the real time forecast run happens (i.e. which corresponding climate lead time to choose in order to get to the calendar weeks). For example, if the sub-seasonal forecast run is on a Wednesday, then the first lead time will be the following Monday-Sunday and the corresponding climatology will have the lead time of days6-12. However, if the forecast date is on Monday, then the first lead time will be days1-7 of the climatology, etc.
- Climate sample:
- The sub-seasonal uses 20 years of hydrological reforecasts with run dates roughly twice a week, using 11 ensemble members. For the climate sample, always we combine 3 run dates are combined, : the actual climate date (we generate the climate for) and one reforecast date before and after. The 3 dates combined will the previous/ following reforecast dates. This is to guarantee more robust estimates of the percentiles (especially the most extreme ones), with no impact on the seasonal variability (i.e. combining too many dates could negatively impact on the behaviour in climate zones with rapid shift between seasons). For example, when generating the climate sample for 15 December 2024, all reforecasts produced for 11, 15 and 19 December will be are used in the climate sample from years 2004-2023 (so, 11 Dec 2004, 11 Dec 2025, ... 11 Dec 2023, then 15 Dec 2004, 15 Dec 2025, ..., 15 Dec 2023, then 19 Dec 2004, 19 Dec 2005, ..., 19 Dec 2023). The total size of the climate sample is 3*20*11 = 660.
- The seasonal also uses 20 years of hydrological reforecasts. For each month, this will mean means 20 sets of reforecasts in the climate sample, using all 25 ensemble members. The total size of the climate sample is 20 * 25 = 500.
- Climate Climatologic distribution: The climate will be climatologic distribution is generated from the climate sample by sorting the 660/500 values for each river pixel. The percentiles then are produced by dividing the climate range into 100 equally likely bins, separated by the percentiles from 1 to 99. The 1st percentile is the value that is exceeded 99% of the time, while the 99th percentile is the value that the reforecasts will exceed only 1% of the time, based on the 20-year climate period. These climate percentiles will be are specific to the 40 possible lead times from days1-7 to days 40-46 and to all reforecast run dates in the sub-seasonal, and will be are specific for all 12 months and for all the 7 monthly lead times.