ISIMIP3a: Unrealistic extreme values found in climate input dataset 20CRv3 #25

Unlike for the other climate input datasets of ISIMIP3a, we did not enforce upper and lower limits on the values of the climate variables when we created the 20CRv3 obsclim dataset. This was intentionally done to provide 20CRv3 data that are as close as possible to the original reanalysis data. As a result of this decision, there are rare unrealistic extreme values in the data. Those are documented in the following, with valid ranges per climate variable defined as follows:

- hurs (%) [1, 100]
- huss (mg kg−1) [0.1, 100000]
- pr (mm day-1) [0, 600]
- ps (hPa) [4.8, 1100]
- rlds (W m-2) [40, 600]
- rsds (W m-2) [0, 500]
- sfcwind (m s-1) [0.1, 50]
- tas, tasmin, tasmax (°C) [-90, 70]

Violations of those valid ranges in 20CRv3 obsclim were only found for the upper limit of hurs, the lower limit of huss, the upper limit of pr, the lower limit of rlds, the upper and lower limit of sfcwind, and the upper limit of tasmax, hence the selection of figures presented below.

The case of hurs > 100 % is special because this variable was not directly provided as output of the 20CRv3 reanalysis. Hence we derived it from huss, ps and tas using the equations of [1] as described in [2] for lack of a potentially more suitable alternative.

Only the few violations of the upper limit of tasmax are inherited by the counterclim, spinclim and transclim versions of 20CRv3, hence no additional figures are presented for those datasets.

[1] Buck (1981) https://doi.org/10.1175/1520-0450(1981)020<1527:NEFCVP>2.0.CO;2
[2] Weedon et al. (2010) https://publications.pik-potsdam.de/pubman/item/item_16400