Reach Scale Hydrology

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Global Reach-level Flood Reanalysis

Global Reach-level Flood Reanalysis

GRFR is a 3-hourly river discharge record globally for 2.94 million river reaches during the 40-year period of 1980-2019. The underlying modeling chain consists of the VIC land surface model (0.05°, 3-hourly) that is well calibrated and bias corrected and the RAPID routing model (2.94 million river/catchment vectors), with precipitation input from MSWEP and other meteorological fields downscaled from ERA5. Flood events (above 2-year return) and their characteristics (number, spatial distribution, and seasonality) were extracted and studied. Validations against 3-hourly flow records  from 6,000+ gauges in CONUS and daily records from 14,000+ gauges globally show good modeling performance across all flow ranges, as well as good skills in reconstructing flood events (high extremes).

Production Method

Similar to the GRADES product, the modeling system consists primarily of a land surface model VIC, a river routing model RAPID, a calibration procedure, and a bias-correction (post-processing) procedure


Globally we compiled daily records over 21,000+ river gauges from multiple sources. We screened the gauges for: (1) gauges located <500 m from closest reach; (2) ≥3 years of valid data during the validation period 1980-2017 (1979 for routing model spin-up, and no data for 2018-2019). The selected gauges (14,000+) cover a range of hydro-climates, stream orders, and basin size. Given the 90 m DEM derived hydrography, we are able to include headwater gauges with very small drainage areas (29% of them <250 km2). In contrast to many previous global studies that validated their results primarily over large basins (Alfieri et al. 2020; Li et al. 2015; Wu et al. 2014), the inclusion of small basins inevitably poses much greater challenges to the modeling system.

Over CONUS, we compiled 3-hourly data over 9,000+ river gauges up to 2019 from the United States Geological Survey (USGS). After a similar screening, 6,000+ gauges match the river reaches being simulated and come with sufficient data for skill analysis.

Here is the daily and monthly validation:

And 3-hourly validation over CONUS:

Flood Reconstruction

Flood events are extracted using 2-year return annual maximum flow as the threshold. Here are the maps of flood threshold values (3-hourly flow values) and event counts over the 40-year period as well as the flood seasonality analysis (mean day-of-year D and seasonal concentration R).


Yang, Y., M. Pan, P. Lin, H. Beck, Z. Zeng, D. Yamazaki, C. David, H. Lu, K. Yang, Y. Hong, and E. Wood, 2021: Global Reach-level 3-hourly River Flood Reanalysis (1980-2019). BAMS,

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