News
Water evaporation follows the sun with a delay
Published: 13 February 2014
Only modeling of all the different ecosystem components (soil, plants, and atmosphere) can fully explain the looping patterns between evapotranspiration and air dryness, according to a paper in JGR-Biogeosciences.
Evapotranspiration is the process of water evaporation from the soil and from plant leaves. Evaporation is larger when the air is dry and warm – conditions that occur around midday and in the afternoon, with plenty of solar radiation. Therefore, evapotranspiration is expected to increase during the morning and decrease in the afternoon. This daily cycle is well-known, but more subtle changes are still not well understood. In particular, evapotranspiration increases fast in the morning and decreases only late in the afternoon, creating clockwise looping patterns when plotted as a function of air dryness.
There are many causes for this looping (or hysteretic) pattern, but they are all inter-related and thus difficult to describe. The paper by Quan Zhang and coworkers recently published in JGR-Biogeosciences addresses this hysteretic pattern by adding one by one all the possible causes in an increasingly complex mathematical model. They show that both the closure of leaf stomata in the afternoon, when the air is driest, and daily changes in soil moisture around the roots play a role.
Stefano Manzoni, who works at the Departments of Crop Production Ecology and Ecology, SLU, coauthored this publication
Links:
stefano.manzoni@slu.se