Latent Heat and Soil Types
Date: December 2007
What are the average latent heat levels for the following
soil types: clay, sand, and silt. My study is focusing on sites with a
northern European climate and figures in MJ/m3 would be appreciated.
Unfortunately I cannot answer your question directly because
latent heat flux is dependent not only on soil type but
on soil moisture content, intensity of solar radiation impinging
on the soil, the temperature of the soil, the composition of the
soil (soils are not generally one pure type, but a mixture of types),
soil texture, and how much surface litter and vegetation is above
the soil surface.
Please excuse me if I repeat things below that you already know,
but we have a wide audience that may not know the following.
One thing that can be said is that soil type does affect evaporation
if all other things are equal. A sandy soil does not hold water
nearly as well as a clay, the water tending to drain out of the
sandy soil whereas clay soils tend to be able to hold more water
and hold it more tightly because the clay particles are smaller
and have smaller spaces between them. Therefore, it is generally more
difficult to evaporate water from a clay soil than from a sandy soil.
As the size of soil particles becomes smaller, the porosity of the
soil becomes larger (indicating the total amount of "air" space
between soil particles), in the order of sand, loam, silt, clay. The
larger the porosity of the soil, the more tightly water is held between
the soil particles, and the more difficult it is for water to drain out
of the soil and for it to be evaporated. Organic matter in the soil
further helps to absorb water and keep it in the soil, so the extent of
organic content is also important in water retention and evaporation.
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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