The Design Document page provides a description of the algorithms, implementation and planned testing including unit, verification, validation and performance testing. Please read Step 1.3 Performance Expectations that explains feature documentation requirements from the performance group point of view.
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Date last modified: 30 August 2021
Contributors: Michael Brunke
ELM generates negative runoffs, especially in the tri-grid configuration. This is coming from the QRGWL, the combined runoff from glaciers, wetlands, and lakes. This goes negative periodically to maintain these features. Figure 1 shows that most of the grid cells generating negative total runoff (blue in panel (a)) occur in areas with lake fraction > ~5%.
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For each requirement, there is a design solution that is intended to meet that requirement. Design solutions can include detailed technical discussions of PDEs, algorithms, solvers and similar, as well as technical discussion of performance issues. In general, this section should steer away from a detailed discussion of low-level software issues such as variable declarations, interfaces and sequencingThe negative contribution to runoff from lakes comes about from assuming a constant lake water storage. Therefore, the water needed to maintain that needs to be taken from the total runoff. If there is excessive evaporation, this can result in negative runoff. To counter this when this feature is turned on, what would go to QRGWL goes to change the lake water storage (WSLAKE): DWSLAKE = ((QIN - EVAP - QRGWL - QSNOWCP) - DWSNO - DWSOI) * dt. If WSLAKE is too low (<5000 mm), QRGWL is set to 0, while the excess water is removed by QRGWL if WSLAKE >= 5000 mm.
Design and Implementation
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Date last modified: 30 August 2021
Contributors: Michael Brunke
Figure 1b shows the total runoff from a test run including lake water storage. The negative runoff from the grid cells with lakes is eliminated. The only negative runoff left is from grid cells containing glaciers.
Planned Verification and Unit Testing
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