land surface models & surface water hydrology cédric david
TRANSCRIPT
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