Impact of wind turbine turbulence on crop canopy dew formation in the US Midwest: Modeling results as a guide to field measurements

Dew characteristics are important in determining crop susceptibility to fungal disease. In recent years, wind farms have rapidly expanded on Midwestern croplands, and future development is projected to meet the growing energy needs. Detection of wind turbine wakes at the ocean surface downstream of offshore wind farms suggests that turbine-generated turbulence will potentially enhance mixing of momentum, heat, CO2, and moisture between crops and the lower levels of the boundary layer. Such modification in the crop canopy may prevent/enhance dewfall occurrence and thus reduce/increase dew amount and the leaf wetness duration. We will present WRF 1-D simulations (including turbine-turbulence-generation formulation) of multiple combinations of wind speed and surface characteristics on the influence of wind turbine impact on dew formation, duration, and dissipation. Several sensitivities will be examined to wind speed: surface roughness, soil moisture, cloudiness, temperature, relative humidity, soil type, and vegetative fraction. The nocturnal temperature and moisture stratification in the layer between the surface and the top of the blades is likely to be a significant factor in wind turbine-wake forcing on dew characteristics. We hypothesize that nighttime conditions of light winds near the surface and moderate winds at the hub height, (a characteristic condition under which turbines generate power in the Midwest), have high impact on vertical profiles of surface-layer moisture and temperature and hence on the development, maintenance, and removal of canopy wetness. Analysis of data from recent and planned field measurements in central Iowa of 10-m wind speed, surface relative humidity, and cloudiness will provide qualitative and semi-quantitative validation to the modeling. Hub-height wind speed and visual observations will indicate the operational mode of the wind turbines.