Impacts of irrigation on land-atmosphere interactions in high-resolution model simulations
Date
2017
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
In the United States, irrigation represents the largest consumptive use of
freshwater and accounts for approximately one-third of total water usage. Irrigation
impacts soil moisture and can ultimately influence clouds and precipitation through
land–planetary boundary layer (PBL) coupling processes. This dissertation is a
collection of three studies that analyze the impact of irrigation on the atmosphere
using NASA modeling tools the Land Information System (LIS) and the NASA
Unified Weather Research and Forecasting Model (NU-WRF) framework. ☐ The first study investigates the effects of drip, flood, and sprinkler irrigation
methods on land–atmosphere interactions, including land–PBL coupling and
feedbacks at the local scale. The offline and coupled simulation results show that
regional irrigation impacts are sensitive to time, space, and method and that irrigation
cools and moistens the surface over and downwind of irrigated areas, ultimately
resulting in both positive and negative feedbacks on the PBL depending on the time of
day and background climate conditions. ☐ The second study assesses the sprinkler irrigation scheme physics and model
sensitivity to choice of irrigation intensity and greenness fraction over a small, high
resolution domain in Nebraska and evaluates the model performance with Cosmic Ray
Neutron Probe (CRNP) observations. Results show that differences between
experiments are small at the interannual scale, but become more apparent at seasonal
and daily time scales. In addition, field-scale heterogeneity resulting from the
individual actions of farmers is not captured by the model and the amount of irrigation
applied by the model exceeds that applied at the two irrigated fields. However, the
seasonal timing of irrigation and soil moisture contrasts between irrigated and nonirrigated
areas are simulated well by the model. ☐ The third study assesses the individual and combined impacts of irrigation and
wind turbines on surface fluxes, near surface temperature, and humidity. Results show
that irrigation repartitions surface sensible and latent heat fluxes, reduces daytime
temperatures and increases temperatures at night. Turbines weaken surface sensible
heat fluxes minimally during the day but enough at nighttime to slightly reduce near
surface temperature. The simulations that include both turbines and irrigation show
that wind power production is slightly reduced when irrigation is included and
irrigation contributes to a greater reduction in daytime surface sensible heat fluxes
than would be realized with only turbines. Taken together, these three studies
showcase the dramatic alterations that irrigation induces to the water and energy
cycles and demonstrates the potential for human impacts on weather and climate.