Natural Resources, School of

 

First Advisor

Rezaul Mahmood

Second Advisor

Trenton Franz

Third Advisor

Michael Hayes

Date of this Version

12-2-2020

Citation

Lachenmeier, E.J., 2020: Impacts of Irrigated Agriculture on the Near Surface and Planetary Boundary Layer Atmosphere: Results from the Great Plains Irrigation Experiment (GRAINEX). M.S. thesis, University of Nebraska-Lincoln

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Natural Resource Sciences, Under the Supervision of Professor Rezaul Mahmood. Lincoln, Nebraska: November, 2020

Copyright © 2020 Emilee J. Lachenmeier

Abstract

Modification of natural prairie grasslands into irrigated and rainfed agriculture in the Great Plains produced significant impacts on regional weather and climate including temperatures, precipitation, energy fluxes, and the planetary boundary layer (PBL) atmosphere. The Great Plains Irrigation Experiment (GRAINEX) during the 2018 growing season collected data over irrigated and non-irrigated crop fields to further understand these impacts. The data were collected during two intensive observation periods (IOPs) in early June (IOP 1: 30 May – 13 June of 2018) and late July (IOP 2: 16 July – 30 July of 2018). The data analyzed include latent (LE) and sensible (H) heat fluxes, air temperature, dew point temperature, specific humidity, equivalent temperature (moist enthalpy) which were assessed using ground based sensors, PBL and lower tropospheric development which was assessed using radiosonde data. In addition, near surface soil moisture data were used to model root zone soil moisture utilizing Wang et al. (2017) Exponential Filter Model. Results show increased partitioning of energy into latent heat compared to sensible heat over irrigated areas. It is particularly noticeable during IOP 2 when, on average LE was about ~15 W m-2 higher than H. At the same time, average maximum air temperature decreased by ~2.75 °C from IOP 1 to IOP 2. Implementation of the Wang et. al (2017) Exponential Filter Model indicated periods of notable drying and wetting throughout the site profiles reflective of an increase in water use by plants and rain or irrigation events. Radiosonde data suggest reduced PBL heights at all launch sites from IOP 1 to IOP 2 with larger changes over irrigated areas (up to ~812 meters). Compared to IOP 1, lifting condensation level (LCL) heights were also lower during IOP 2 over irrigated areas. In addition, six one-day case studies were completed to further understand land-atmosphere (L-A) interactions in the context of irrigated and non-irrigated land uses. They further corroborate IOP-wide results.

Advisors: Rezaul Mahmood and Trenton Franz

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