Microclimate Modification by Slat‐fence Windbreaks¹

Abstract

Abstarct The influence of windbreaks on the microclimate has been widely studied, but more information is needed on the dynamics of wind barriers and how they modify the microclimate. Meteorological parameters were measured in the spatial vicinity of slat‐fence windbreaks of 0, 40, and 60% porosity to characterize microclimate modification by windbreaks of various porosities. The highest daytime air temperature, lowest nighttime air temperature, and generally the greatest vertical temperature differences all occurred in the area of lowest windspeed. However, lowest windspeeds occurred at different locations for the different porosity windbreaks. The water‐vapor‐pressure and vapor‐pressure differences between 40 and 5 cm above the crop surface were greatest at 2H leeward of the solid and 40‐percent‐open barriers throughout most of the daylight hours, whereas the vapor pressure at 2H leeward of the 60‐percent‐open barrier was similar to vapor pressure at other leeward positions. The vapor pressure was lower at 12H leeward of all barriers than in the open field Bowen ratios indicated that evapotranspiration was greater in the sheltered area than in the open, contrary to our earlier findings of less evaporation from evaporimeters leeward of similar barriers. Possible explanations of this anomaly are lower potential evaporation in the shelter, leaving the plants more passive to transpiration, and unaccounted‐for horizontal divergence of sensible and latent heat in the sheltered area.