Pan-evaporation measurements and Morton-point potential evaporation estimates in Australia: are their trends the same?

This paper compares Australian pan-evaporation (E-pan) observations with point potential evaporation (E-p) estimates derived using the Morton method. In particular, it focuses on trends in both E-p and E-pan. E-p is defined as the potential evaporation from an area which is so small that the effects of the evaporation on the overpassing air would be negligible, while E-pan is evaporation measured using a standard pan. The analyses are based on monthly data from 28 sites and refer to the period 1970-2004. The results show that E-p and E-pan are strongly correlated on the monthly time scale. Furthermore, the sign of the monthly trends are in agreement, on average, at 60% of the sites. Where there is agreement, positive trends outweigh negative trends. This is consistent with the fact that although trends in E-pan and E-p varied from site to site and from month to month, the median trends were positive except for December. The correlation between the trends in both quantities across all sites is statistically significant (R = 0.5 1) which indicates that projected changes based on climate model outputs can be used to estimate changes in future potential evaporation. Copyright (C) 2008 Royal Meteorological Society