Practical and Applied Hydrometeorology

As simple as it sounds, it’s actually quite challenging to measure the impact plants have on the atmosphere. As plants absorb carbon dioxide and release oxygen and water into the air around them, they have a constant effect on local conditions. But how much of an effect? And, how much impact does a given patch of plants and soil have on reducing atmospheric CO₂?

 

To enable students to answer these questions, SNRE Professor Shirley Kurc offered the Practical & Applied Hydrometerology course in collaboration with Dr. Jim Shuttleworth, Hydrology and Water Resources. The class gives students both the practice and the context necessary to use, and interpret the data from an eddy covariance tower.

 

Eddy covariance towers are in place across the globe and produce large amounts of publicly available data on evapotranspiration and carbon exchange between land and air (for example see Fluxnet, Ameriflux, CarboEurope, Fluxnet Canada, or iLEAPS).

 

To do this, the towers take advantage of the fact that air is constantly moving in spirals of various sizes, called eddies. By measuring the amount of water in air that is moving up from the ground and in air that is moving down towards the ground, an eddy covariance tower can estimate how much water plants are releasing (the rate of evapotranspiration). Similarly, the towers can determine how much CO₂  plants are absorbing from the air. In addition, eddy covariance towers measure traditional meteorological data: air temperature, precipitation, solar radiation, relative humidity, wind speed and wind direction.

 

Dr. Kurc gave students a strong background in the method used to derive the data, the assumptions of the method. She and the class then installed two eddy covariance towers at Biosphere 2, where they tested the effectiveness of the method in a relatively confined area (similar to an urban installation). They took hand measurements of soil moisture and precipitation and compared the results from the two towers to validate the use of eddy covariance towers in confined spaces. Since the area they studied was an irrigated lawn, they provided recommendations for irrigation regimes and the potential impacts of salt accumulation to the property managers.

 

Eddy covariance towers have been widely tested and used in boreal and tropical forests, but less is known about their use in dryland ecosystems. It is also not clear how the towers would work in more confined, urban areas. Carbon uptake by plants both in drylands and in cities is becoming increasingly considered as potential offsets for carbon emissions. University of Arizona graduate students are now in a position to try out these powerful instruments in new systems and to draw on the wealth of publicly available data.