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 layerGround

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

kQ P

Pressure at upper layer Pu

Soil (Permeability k)

Q

Pressure at lower layer Pl

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

• RunoffSimple 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 groundwaterGround

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

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