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Land Surface Models & Surface Water Hydrology

Land Surface Models & Surface Water Hydrology. Cédric DAVID. Outline. 1. Introduction 2. Basic Models 3. Areas of improvement 4. Conclusions. 1. Introduction. Land covers 30% of the Earth’s surface Shelter for human beings Storage of freshwater (essential for human life)

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Land Surface Models & Surface Water Hydrology

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  1. Land Surface Models &Surface Water Hydrology Cédric DAVID

  2. Outline • 1. Introduction • 2. Basic Models • 3. Areas of improvement • 4. Conclusions

  3. 1. Introduction • Land covers 30% of the Earth’s surface • Shelter for human beings • Storage of freshwater (essential for human life) • Greater variability of weather above land than oceans Understanding land surface processes is crucial for human life

  4. 1. Introduction How do Land Surface Models handle Surface Water Hydrology?

  5. Outline • 1. Introduction • 2. Basic Models • 3. Areas of improvement • 4. Conclusions

  6. Precipitation Evaporation Runoff Bucket capacity Water level in bucket 2. Basic Models • Bucket model • Most simple model • Fixed water capacity • No soil charaterictics • No vegetation

  7. The Biosphere Atmosphere Transfer Scheme (BATS) Three soil layers One vegetation layer Vegetation layer Upper soil layer Root zone layer Ground Total active layer 2. Basic Models

  8. SiB (Simple Biosphere) Two vegetation layers Three soil layers Trees and shrubs Grass Upper thin soil layer Root zone layer Ground Recharge layer 2. Basic Models

  9. 2. Basic Models • Bucket, BATS and SiB models are 1-D models (vertical) • Ignore horizontal interactions between adjacent cells • Used in 3-D atmospheric models • Only three land components (soil, snow and vegetation) • No vegetation types • No runoff

  10. Outline • 1. Introduction • 2. Basic Models • 3. Areas of improvement • 4. Conclusions

  11. 3. Areas of improvement • Moisture • Runoff • Snow

  12. Soil (Permeability k) Pressure at upper layer Pu Q Pressure at lower layer Pl 3. Areas of improvement • Moisture • Darcy’s law

  13. 3. Areas of improvement • Moisture • Infiltration excess runoff (Liang and Xie)infiltration is a function of the soil and of the soil moisture • Moisture excess runoff (Liang and Xie) • Niu and Yang (2006): Gravity Recovery And Climate Experiment (GRACE) compared to Noah (seasonal variability of TWS)

  14. 3. Areas of improvement • Runoff • Boone et al. (2004) Comparison of LSMs  good estimates of runoff

  15. Upper layer: Vegetation canopy and soil surface Lower layer: Root zone and groundwater Ground 3. Areas of improvement • Runoff Simple Water Balance • Schaake et al. (1996) Simple Water Balance • Understand surface runoff processes  runoff estimates comparable to more advanced models

  16. 3. Areas of improvement • Snow • Ek et al. (2003): • snowpack physics (snow albedo and conductivity) • Snow cover fraction  Improvement of wintertime conditions forecast

  17. Outline • 1. Introduction • 2. Basic Models • 3. Areas of improvement • 4. Conclusions

  18. 4. Conclusions • Land surface models = crucial component of atmospheric models • Basic models exist and can be improved • Variety of improvements each serving its own purpose

  19. Thank you!Questions?

  20. 3. Areas of improvement • Sub-grid scale variability • component approach • tile approach • statistical approach

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