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DOE Pulse
  • Number 393  |
  • July 22, 2013

Irrigation's impact on clouds and climate

Crop irrigation is one of the largest ways humans perturb the climate. Including irrigation in model calculations will help bring model estimates closer to a complete representation of the climate.

Crop irrigation is one of the largest ways
humans perturb the climate. Including
irrigation in model calculations will help
bring model estimates closer to a complete
representation of the climate.

From corn to cotton, irrigation water is needed to grow crops around the world and that same water alters the balance of moisture in soil and the climate, according to scientists at DOE’s Pacific Northwest National Laboratory. Irrigation shifts the balance of water vapor and upward moving air. The impact, seen in dry years especially, is on the layer of air closest to us, which is most susceptible to heat exchange and evaporation from the Earth's surface. In particular, irrigation may play a role in forming shallow clouds, which alter the local climate.

The PNNL team led the study to incorporate an irrigation representation into the Weather Research and Forecasting  regional climate model. This included adding "sensors" and "triggers" in the model, similar to those used by farmers and others, to detect the need and timing for optimal water use. They evaluated the performance of the improved model in simulating the regional climate and surface water and energy budgets over the Atmospheric Radiation Measurement Southern Great Plains site. The team conducted a series of simulations with and without irrigation over the Great Plains for both an extremely dry year (2006) and wet year (2007).

To create a benchmark for their model, the team retrieved and processed a large amount of observational data from the ARM archive, including soil moisture and temperature, surface fluxes, and meteorological conditions. These data are from the ARM Eddy Correlation Flux Measurement system, the Energy Balance Bowen Ratio station, the Soil Water and Temperature System, the Surface Meteorological Observation Systems, and the Oklahoma Mesonet.

The team's results demonstrate that including a realistic irrigation representation in climate studies improves the depiction of the role of human activities in modulating land-air-cloud interactions and regional climate.

Future work will extend the time and increase the area studied. The next study will include the hydrologic responses, such as runoff and streamflow over land and atmospheric processes above the boundary layer. They will also evaluate the impact of model resolution and model physics, identified as the biggest sources of uncertainty in the existing modeling studies on irrigation effects.

DOE’s Office of Science Biological and Environmental Research Atmospheric System Research program funded the research. The Oklahoma Mesonet Program is supported by the State of Oklahoma.  

[Kristin Manke, 509.372.6011,
kristin.manke@pnnl.gov]