Assessment of pan evaporation changes in South Western Iran

Evaporation is an important component in irrigation scheduling. Due to climate change, understanding of change in evaporation is critical for long term agricultural and environmental planning. The objective of this research is the investigation of temporal and spatial changes in pan evaporation in the Karun & Dez watershed. Our criteria to choose stations are access to data and suitable statistical record length. Geographic, seasonal and annual changes are studied in this research. As a result of performing trend tests, negative trend is found in 66% of the studied seasonal and annual time series, while the remaining cases had positive trends. Investigated time series showed 26 and 12% statistically significant negative and positive trends, at the 0.95 confidence level, respectively and the remaining 62% of time series had non-significant trends. Lali and Abbaspour stations have highest negative and positive slope in most studied time series respectively. Stations in the centre of the watershed showed positive trends while others showed negative or no trends.   Key words: Pan evaporation, trend, south western Iran.