A comparison of moderate and extreme ERA-5 daily precipitation with two
observational data sets
Abstract
A comparison of moderate to extreme daily precipitation from the ERA-5
reanalysis by the European Centre for Medium-Range Weather Forecasts
(ECMWF) against two observational gridded data sets, EOBS and CMORPH, is
presented. We assess the co-occurrence of precipitation days and compare
the full precipitation distributions. The co-occurrence is quantified by
the hit rate. An extended generalized Pareto distribution is fitted to
the positive precipitation distribution at every grid point and
confidence intervals of quantiles compared. The Kullback-Leibler
divergence is used to quantify the distance between the entire extended
generalized Pareto distributions obtained from ERA-5 and the
observations. For days exceeding the local 90th percentile, the mean hit
rate is 65% between ERA-5 and EOBS (over Europe) and 60% between ERA-5
and CMORPH (globally). Generally, we find a decrease of the
co-occurrence with increasing precipitation intensity. The agreement
between ERA-5 and EOBS is weaker over the southern Mediterranean region
and Iceland compared to the rest of Europe. Differences between ERA-5
and CMORPH are smallest over the oceans. Differences are largest over
North-West America, Central Asia and land areas between 15°S and 15°N.
The confidence intervals on quantiles are overlapping between ERA-5 and
the observational data sets for more than 80% of the grid points on
average. The intensity comparisons indicate an excellent agreement
between ERA-5 and EOBS over Germany, Ireland, Sweden and Finland, and a
disagreement over areas where EOBS uses sparse input stations. ERA-5 and
CMORPH precipitation intensity agree well over the mid-latitudes and
disagree over the tropics.