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) Greater variability of weather above land than oceans Understanding land surface processes is crucial for human life

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

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

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

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

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

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

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

3. Areas of improvement Moisture Runoff Snow

3. Areas of improvement Moisture –Darcy’s law Pressure at upper layer P u Soil (Permeability k) Q Pressure at lower layer P l

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)

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

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 Upper layer: Vegetation canopy and soil surface Lower layer: Root zone and groundwater Ground

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

Outline 1. Introduction 2. Basic Models 3. Areas of improvement 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

Thank you! Questions?

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