Open AccessContinental‐scale water and energy flux analysis and validation for North American Land Data Assimilation System project phase 2 (NLDAS‐2): 2. Validation of model‐simulated streamflow
Author(s) -
Xia Youlong,
Mitchell Kenneth,
Ek Michael,
Cosgrove Brian,
Sheffield Justin,
Luo Lifeng,
Alonge Charles,
Wei Helin,
Meng Jesse,
Livneh Ben,
Duan Qingyun,
Lohmann Dag
Publication year - 2012
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011jd016051
Subject(s) - streamflow , evapotranspiration , environmental science , data assimilation , surface runoff , climatology , anomaly (physics) , drainage basin , coupled model intercomparison project , hydrology (agriculture) , geology , climate model , climate change , meteorology , geography , physics , ecology , oceanography , cartography , geotechnical engineering , condensed matter physics , biology
This is the second part of a study on continental‐scale water and energy flux analysis and validation conducted in phase 2 of the North American Land Data Assimilation System project (NLDAS‐2). The first part concentrates on a model‐by‐model comparison of mean annual and monthly water fluxes, energy fluxes and state variables. In this second part, the focus is on the validation of simulated streamflow from four land surface models (Noah, Mosaic, Sacramento Soil Moisture Accounting (SAC‐SMA), and Variable Infiltration Capacity (VIC) models) and their ensemble mean. Comparisons are made against 28‐years (1 October 1979–30 September 2007) of United States Geological Survey observed streamflow for 961 small basins and 8 major basins over the conterminous United States (CONUS). Relative bias, anomaly correlation and Nash‐Sutcliffe Efficiency (NSE) statistics at daily to annual time scales are used to assess model‐simulated streamflow. The Noah (the Mosaic) model overestimates (underestimates) mean annual runoff and underestimates (overestimates) mean annual evapotranspiration. The SAC‐SMA and VIC models simulate the mean annual runoff and evapotranspiration well when compared with the observations. The ensemble mean is closer to the mean annual observed streamflow for both the 961 small basins and the 8 major basins than is the mean from any individual model. All of the models, as well as the ensemble mean, have large daily, weekly, monthly, and annual streamflow anomaly correlations for most basins over the CONUS, implying strong simulation skill. However, the daily, weekly, and monthly NSE analysis results are not necessarily encouraging, in particular for daily streamflow. The Noah and Mosaic models are useful (NSE > 0.4) only for about 10% of the 961 small basins, the SAC‐SMA and VIC models are useful for about 30% of the 961 small basins, and the ensemble mean is useful for about 42% of the 961 small basins. As the time scale increases, the NSE increases as expected. However, even for monthly streamflow, the ensemble mean is useful for only 75% of the 961 small basins.