GloFAS Seasonal v1.0

GloFAS Seasonal v1.0 was launched in November 2017 and its last forecast issued in Nov 2018

GloFAS Seasonal v1.0 technical settings

GloFAS Seasonal v1.0 uses the Lisflood river routing model (van der Knijff et al., 2010) to propagate along the river channel the surface and sub-surface runoff forecasts of the HTESSEL land surface model ( Balsamo et al., 2009) of the ECMWF SEAS5 seasonal forecasting system and to produce daily discharge forecasts. In GloFAS Seasonal v1.0, Lisflood configuration uses expert-defined parameters which are uniform across the entire geographical domain, regardless of land surface characteristics. Results are presented as weekly averages, starting every Monday.

SEAS5 runoff ensemble has 51 members at ~36 km horizontal resolution, which are resampled to 0.1 spatial resolution (~10 km) before being used as daily input to Lisflood. In GloFAS Seasonal v1.0, only the first 16 weeks (out of the available 7 months) of SEAS5 are used.

GloFAS Seasonal v1.0 initial conditions (atmosphere and land surface states from which to start the ensemble discharge forecast) are based on a monitoring analysis of the latest observations, the ERA5 ECMWF reanalysis, using a configuration as close as GloFAS Seasonal v1.0 operational. In practice, GloFAS Seasonal v1.0 initial conditions are taken as GloFAS 30-day v1.0 hydrological reanalysis generated in near-real time.

The GloFAS system
Schematic of GloFAS Seasonal v1.0.

GloFAS Seasonal v1.0 reference discharge runs

GloFAS Seasonal v1.0 hydrological reanalysis is a long deterministic hydrological simulation based on ERA5, the latest atmospheric reanalysis product of ECMWF available in 2018. ERA5 has a horizontal resolution of ~32 km (see Hersbach and Dee 2016 for further reading). GloFAS Seasonal v1.0 hydrological reanalysis covers three separate periods (1990-1992, 2000-2007, 2010-2016). Note that GloFAS Seasonal v1.0 hydrological reanalysis uses the uncalibrated version of Lisflood and is different from GloFAS 30-day v2.0 hydrological reanalysis.

GloFAS Seasonal v1.0 forecast reruns are forecast simulations performed for a set of past dates (1990-1992, 2000-2007, 2010-2016) using ECMWF Seasonal forecasting system SEAS5, based on a configuration as close as possible to GloFAS Seasonal v1.0 operational setting. They are initialised from GloFAS Seasonal v1.0 hydrological reanalysis. They are used to compute GloFAS Seasonal v1.0 discharge thresholds and to analyse GloFAS Seasonal v1.0 forecast skill systematically over a long period.

GloFAS Seasonal v1.0 discharge thresholds are discharge magnitude corresponding to fixed percentile values, derived from the 18-year GloFAS Seasonal v1.0 forecasts reruns separately for each month of the year and each weekly lead-time. GloFAS Seasonal v1.0 discharge thresholds are used to generate river flow anomaly forecast maps.

GloFAS Seasonal v1.0 products

GloFAS Seasonal v1.0 products are generated by comparing, for each lead-time to 16 weeks, the 51 scenarios of GloFAS Seasonal v1.0 weekly-averaged river discharge forecasts to the corresponding GloFAS Seasonal v1.0 discharge thresholds. They include exceedance probability maps and weekly forecast hydrographs, and are available on the 10th of each month through the GloFAS map viewer.

GloFAS Seasonal v1.0 available data

GloFAS Seasonal v1.0 is not available to users.

GloFAS Seasonal v1.0 skill

GloFAS Seasonal v1.0 evaluation was designed to measure the ability of the forecasts to predict the correct category of an ‘event’ compared with a very simple forecast corresponding to long-term average weekly discharge from GloFAS Seasonal v1.0 hydrological reanalysis (used as a benchmark forecast). In other words, to measure if GloFAS Seasonal v1.0 could better predict when weekly-averaged river flow is above the high flow threshold (or below the low flow threshold) than the benchmark forecast. This was done for each week out to 16 weeks using GloFAS Seasonal v1.0 forecast reruns. Results are presented as the longest lead time when GloFAS Seasonal v1.0 is a better forecast than the climatology (defined as the area under ROC curve (AROC) > 0.6). The left hand side plots refer to the high flow threshold, while the right hand side ones for the low flow threshold. The seasons are displayed from top to bottom as MAM, JJA, SON and DJF.

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