Dynamics of Water Vapor Content around Isolated Sprinklers: Description and Validation of Model

Irrigation consumes considerable water to satisfy the current food demand. An improvement in water use efficiency for irrigation is essential. Wind drift and evaporation losses reduce the water use efficiency of center pivot irrigation systems in arid and semi-arid areas. In this paper, a model of water vapor dynamics during and after overhead sprinkler irrigation was developed and validated by experimental data using a center pivot simulator and a water vapor measuring system. The model was represented as an exponential equation during irrigation and a logistic equation after irrigation. The water vapor dynamics measured next to and 2 m from the sprinkler were well-fitted with the developed model. Model performance was good according to evaluations of the Nash—Sutcliffe efficiency coefficient, with values of 0.961 and 0.934 for estimations next to the sprinkler and 2 m from the sprinkler, respectively. Results showed that both modeled and observed water vapor dynamics increased rapidly as irrigation started, and then leveled off to maximum values. After irrigation, the water vapor dynamics started to decrease gradually, and eventually decreased rapidly. The decreasing rate stopped when the water vapor content was restored to the level of the surrounding atmosphere. The model parameters showed that the maximum increases in water vapor content were from 2.506 to 6.476 g m−3 for the area next to the sprinkler, and 1.277 to 3.380 g m−3 for the area 2 m from the sprinkler, under the influence of vapor pressure deficits. The increasing and decreasing rates of the dynamics during and after irrigation were influenced by temperature, relative humidity, and vapor pressure deficits, according to Pearson’s correlations. A period of 2.3 to 4.0 h was required to restore water vapor to the atmospheric level.