Monthly routed streamflow at each gauge’s MERIT reach is compared with observed flow over water years 1981-2018, using NSE, KGE and percent bias.
Observations
Daily multi-agency streamflow, 2,311 sites (flow_multi_agency_1965-10-01_2024-09-30.nc, m³/s), resampled to monthly means.
A crosswalk (flow_multi_agency_all_meta.csv) links each gauge to its MERIT reach (merit_reach_id) and labels it naturalized or observed.
2,257 of the 2,311 gauges have overlapping records and are evaluated.
Matching model and observations
Model: mizuRoute RoutedRunoff at the gauge’s reach, monthly.
Time: mizuRoute stamps each month on day 16 and observations on day 1, so both are placed on a monthly period index before comparison.
Metrics use only the months common to the observations and every configuration being compared.
Metrics
NSE (Nash-Sutcliffe efficiency): 1 is perfect; below 0 is worse than the observed mean.
KGE (Kling-Gupta efficiency): combines correlation, variability ratio and bias.
PBIAS: percent bias in mean flow.
NSE_stable: NSE reported only for records of 60 months or more. Short, low-variance records can give extreme values (one 24-month record scores NSE = −452,139).
How gauges are counted. Metrics come from each configuration’s <config>_streamflow_eval.csv (analysis/streamflow/ctsm_streamflow_eval.py). All five configurations are scored on the same gauges and the same months per gauge. At each gauge a configuration is better than its baseline when NSE or KGE is higher, or abs(PBIAS) is smaller. Two counts are reported:
Strict: any change in that direction.
Material: a change larger than 0.01 in NSE or KGE, or 1 percentage point in abs(PBIAS); smaller changes count as neither.
Basin-averaged CTSM fields. To explain streamflow errors, CTSM variables (precipitation, ET, snow, soil moisture, runoff and others) are averaged over each gauge’s full contributing area.
Grid-to-catchment weights: spatialweights_nldas0.125_to_merit_nldas.nc.
Upstream catchments: the augmented MERIT topology (ntopo_MERIT_Hydro_v1_aug.nc, allUpSegIndices).
Contributing areas span 26 to 1,339,481 km²; the median basin covers 11 grid cells.
Derived fields: PRECIP = RAIN + SNOW, SOILMOIST = TOTSOILLIQ + TOTSOILICE, and WBAL = PRECIP − ET − QRUNOFF.