Evaluation of the hydrological cycle in reanalyses and observations
- Publication date
- 1 January 1997
- Publisher
- An evaluation of the components of the hydrological cycle in the reanalyses from the ECMWF has been performed. These are compared to the reanalyses from NCEP and NASA as well as analyses and observations from different data sources and several satellite estimates. With respect to GPCP precipitation data, the ECMWF reanalyses are superior to the rean- alyses from NCEP and NASA in the extratropics. No clear decision can be made in the tropics where all reanalyses overestimate precipitation. The NASA reanalysis does not catch correctly the annual cycle of tropical precipitation. There are some problematic regions in the ECMWF reanalysis, including the Andes, where too much precipitation is analyzed, and the Alps and Antarctica which are too dry. There is a 100 southward shift of the ITCZ over Africa in the ECMWF reanalysis around 1987. A probably non—meteorological long term trend is visible in the tropics with a slight increase of oceanic precipitation and a decrease of latent heat flux. The reason for this is not clear. Therefore there are applications for which the NCEP reanalyses may be more suitable. The quality of the hydrological cycle has been appraised by long—term means of the difference of precipitation and evaporation (P-E) and a comparison to observed river discharge. None of the reanalyses has a closed hydrological budget over subtropical land points. The 12-24 hour forecast of ECMWF performs best in this respect. The ECMWF reanalysis shows a clear spinup of about 15% nearly everywhere. On the whole, especially in winter over land, the 12 to 24 hour forecasts fit the observations best and give the most consistent picture. A positive effect on the construction of global precipitation datasets (as filling data sparse areas in the GPCP analyses) is likely.
