Hydrological Influence of Wetland and Depression Water Storage in the World’s Major River Basins: The Upper Mississippi River Basin Modeling Experiment

Abstract:

Observations and simulations of floods, droughts and water availability typically underscore the influence of large, managed water bodies (such as lakes and reservoirs). Surface water storage in small yet abundant landscape depressions – including wetlands and other small waterbodies – is largely disregarded in conventional practices for hydrologic modeling and analysis. No quantitative evidence exists of how their exclusion may lead to potentially inaccurate predictions and understanding of hydrologic dynamics in response to variations in climate and land cover changes across the world’s major river basins. To fill this knowledge gap, we recently developed the first-ever surface depression-integrated large-scale modeling approach, focusing on the ~450,000 km² Upper Mississippi River Basin (UMRB) in the United States. We applied an efficient topography-based algorithm to estimate areas and volumes of ~455,000 surface depressions across the UMRB and then aggregated their effects per subbasin. Compared to a “no depression” conventional model, our depression-integrated model (i) improved streamflow simulation accuracy with increasing upstream abundance of depression storage, (ii) significantly altered the spatial patterns and magnitudes of water yields across 315,000 km² (70%) of the basin area, and (iii) provided realistic spatial distributions of rootzone wetness conditions corresponding to satellite-based data. These findings provide us with new insights on the effects of wetland and depression storage and stimulates a reassessment of current conventional practices for large-scale hydrologic modeling and management.