Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

An analysis of pan evaporation by synoptic weather types revealed that pan evaporation rates vary significantly by weather type conditions. Fair weather types are associated with the greatest evaporation rates as was expected, and stormy weather types with the least. These findings are primarily related to the variation of solar radiation by weather type. An investigation of the relationship of pan evaporation to solar radiation by synoptic weather types revealed that the ratio of pan evaporation, expressed in energy units, to incoming solar radiation, also varies considerably by synoptic weather types. In general it was found that stormy weather types are associated with the highest ratios of pan evaporation to solar radiation. Fair weather types are associated with lower ratios, with Continental High situations resulting in the lowest ratios of pan evaporation to solar radiation in general. An evaluation of potential evapotranspiration models by synoptic weather types revealed that models perform differently for varying weather type conditions. For example, temperature based models perform well during stormy weather conditions since they are unaffected by low levels of solar radiation, but do not perform as well for fair weather conditions. Models based on solar radiation perform well during fair weather, but performance is reduced when stormy weather conditions prevail. The results of this research have increased understanding of the variability of evaporation under different weather conditions and the variability of potential evapotranspiration model performance under varying weather conditions. Further research of the variability of pan evaporation and evapotranspiration by synoptic weather types will lead to improved potential evapotranspiration model evaluation, will aid potential evapotranspiration model selection and application and will permit potential evapotranspiration model modification for increased performance under certain weather conditions.

Pages

172

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