AGRON 505 Recap: Land Surface Modeling
Jason Patton
April 30, 2013
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Importance of Models
In this course, we have discussed many models regarding the land surface, particularly with
a focus towards the modeling of mass and energy fluxes. Why are these models important?
For example, if you are...
• a meteorologist, you may want to know how much moisture and/or heat is entering
the boundary layer from the surface;
• an agronomist, you may want to know how much water crops require to stay at optimum leaf temperature and to be productive;
• a hydrologist, you may want to know whether precipitation will infiltrate to the soil or
run o↵ in to a nearby stream; or
• a soil physicist, you may want to know how much demand there is to evaporate and
transpire water from the soil.
This list by no means exhausts who might be interested in this course’s topics nor why they
might be interested, but should give an idea about how some of the topics discussed in class
may relate to your field of study.
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Simplicity of Models
An important aspect of the models discussed in class is that they are very simple models,
requiring minimal inputs (air temperature, canopy temperature, humidity, wind speed, net
radiation) to predict a large number of fluxes or other processes. All of the inputs needed
for our models can be measured or estimated from basic, hourly-reporting meteorological
stations. This compares to more complex (but slightly more realistic) models, such as the
ones discussed during the turbulence lectures, that require expensive equipment that must
accurately record data every tenth of a second.
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Model Recap
Let’s recap some the models we have discussed in class:
• thermal time (Chapter 2)
• sensible heat flux (Chapters 6, 7)
• latent heat flux/evapotranspiration (Chapters 3, 6, 7, 14)
• soil heat flux (Chapter 8)
• soil water flux (Chapter 9)
• radiation fluxes (Chapters 10, 11)
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Land Surface and Crop Modeling
By putting together all of the models above, we can come up with a land surface model.
Land surface models are often coupled with weather and climate models to account for the
exchange of mass and energy between the atmosphere and land surface. We could also come
up with a crude version of a crop model. Crop models are used to prediction the impact of
weather (and other conditions related to crop growth) on crop yields.
Agro-IBIS is a model that combines aspects of both land surface models and crop models.
A diagram of the model used in Agro-IBIS can be seen in Figure 1. The idea behind most
land surface models is that the land surface is broken up in to two or more control volumes:
one (or more) representing the canopy above the soil surface, one (or more) representing
the soil. Heat and mass fluxes are transferred between each volume or out of the top or
bottom volume. Agro-IBIS, by default, uses two control volumes (or “layers”) to represent
the canopy and five layers to represent the soil.
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Figure 1: A diagram showing the models used in Agro-IBIS. Can you identify where some of the models
we discussed in class might be used?
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