Heat island and oasis effects of vegetative canopies: micro-meteorological field-measurements
Dry-bulb temperature, dew-point, wind speed, and wind direction were measured in and around an isolated vegetative canopy in Davis CA from 12 to 25 October 1986. These meteorological variables were measured 1.5 m above ground along a transect of 7 weather stations set up across the canopy and the upwind/downwind open fields. These variables were averaged every 15 minutes for a period of two weeks so we could analyze their diurnal cycles as well as their spatial variability. The results indicate significant nocturnal heat islands and daytime oases within the vegetation stand, especially in clear weather. Inside the canopy within 5 m of its upwind edge, daytime temperature fell by as much as 4.5°C, whereas the nighttime temperature rose by 1°C. Deeper into the canopy and downwind, the daytime drop in temperature reached 6°C, and the nighttime increase reached 2°C. Wind speed was reduced by ~ 2 ms-1 in mild conditions and by as much as 6.7 ms-1 during cyclonic weather when open-field wind speed was in the neighborhood of 8 ms-1. Data from this project were used to construct correlations between temperature and wind speed within the canopy and their corresponding ambient, open-field values.