GloFAS-ERA5 operational global river discharge reanalysis 1979-present
2020
Abstract. Estimating how much water is flowing through rivers at
the global scale is challenging due to a lack of observations in space and
time. A way forward is to optimally combine the global network of earth
system observations with advanced numerical weather prediction (NWP) models
to generate consistent spatio-temporal maps of land, ocean, and atmospheric
variables of interest, which is known as a reanalysis. While the current generation
of NWP models output runoff at each grid cell, they currently do not produce river
discharge at catchment scales directly and thus have limited utility in
hydrological applications such as flood and drought monitoring and
forecasting. This is overcome in the Global Flood Awareness System (GloFAS;
http://www.globalfloods.eu/ , last access: 28 June 2020) by coupling surface and
sub-surface runoff from the Hydrology Tiled
ECMWF Scheme for Surface Exchanges over Land (HTESSEL) land surface model used within ECMWF's
latest global atmospheric reanalysis (ERA5) with the LISFLOOD hydrological
and channel routing model. The aim of this paper is to describe and evaluate
the GloFAS-ERA5 global river discharge reanalysis dataset launched on 5 November 2019 (version 2.1 release). The river discharge reanalysis is a
global gridded dataset with a horizontal resolution of 0.1 ∘ at a
daily time step. An innovative feature is that it is produced in an
operational environment so is available to users from 1 January 1979 until
near real time (2 to 5 d behind real time). The reanalysis was evaluated
against a global network of 1801 daily river discharge observation stations.
Results found that the GloFAS-ERA5 reanalysis was skilful against a mean
flow benchmark in 86 % of catchments according to the modified
Kling–Gupta efficiency skill score, although the strength of skill varied
considerably with location. The global median Pearson correlation
coefficient was 0.61 with an interquartile range of 0.44 to 0.74. The
long-term and operational nature of the GloFAS-ERA5 reanalysis dataset
provides a valuable dataset to the user community for applications ranging
from monitoring global flood and drought conditions to the identification of
hydroclimatic variability and change and as raw input for post-processing
and machine learning methods that can add further value. The dataset is
openly available from the Copernicus Climate Change Service Climate Data
Store: https://cds.climate.copernicus.eu/cdsapp#!/dataset/cems-glofas-historical?tab=overview (last access: 28 June 2020) with the following DOI: https://doi.org/10.24381/cds.a4fdd6b9 (C3S, 2019).
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