SENSITIVITY OF SIMULATED DEW DURATION TO METEOROLOGICAL VARIATIONS INDIFFERENT CLIMATIC REGIONS OF CALIFORNIA

A previously verified and validated model was used in combination with hourly weather data to simulate the frequency and duration of dew occ urrence over one growing season (April-October) al four sites under co astal fogbelt, coastal valley, and interior valley climates in Califor nia. Simulation results indicated similar values of dew occurrence (78 -93% of the days) and mean dew duration (8.7-9.3 h day(-1) or 9.7-11.2 h per dew event) at the coastal stations, despite high day-to-day var iability and steep climatic gradients between these sites. Dew periods at the interior valley site, where occurrence of dew was predicted on only 23% of the days, were much shorter (mean 0.9 h day(-1) or 3.7 h per dew event). The data displayed moderate seasonal trends, with the longest dew periods occurring in fall at the coastal stations and in s pring at the interior valley station. Simulated dew durations showed f avorable agreement with measured dew durations in an independent valid ation study. Based on real-system weather data and simulated dew data, sensitivity analyses were performed to compare the effects of tempera ture, atmospheric humidity (vapor pressure), cloud cover, and wind spe ed on dew duration at the four test sites. The results showed simulate d dew durations most sensitive to changes in humidity and cloud cover at the coastal sites and to humidity and wind speed at the interior va lley site. Relative sensitivity values were generally highest during t he summer months (June-August). Spatial variations (i.e. differences b etween locations) and seasonal variations (i.e. differences between di fferent seasons at the same site) of relative sensitivity Values had a pproximately the same magnitude.