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A user of our ERA-Interim dataset asked: How does ERA-Interim deal with lakes, specifically Lake Victoria?

  • Is it open water (not eg. some kind of marsh)?
  • If yes, where does its surface temperature come from?


The answer from our scientists:

In ERA-Interim the surface water temperature of Lake Victoria and most open-water bodies (with the exception of US Great-lakes) are specified by a monthly climatology and therefore will not display any variability year-after-year which might be particularly inaccurate in anomalously warm years.

The climatology was generated by a 2m temperature gridded field (at low resolution of about 1degree) lagged by one month to represent some of the thermal inertia effect of lakes. Over lake Victoria that is particularly poor due to orography discrepancy of the lake surface elevation.

Lake Victoria temperatures are expected to be more accurate in the upcoming ERA5 reanalysis (in which lake thermodynamics is represented by a dedicated scheme). It is recommended to keep an eye on this new reanalysis and for any new research use the ERA5 test dataset already made available at