HR: 1340h
AN: H33B-1259    [Abstracts]
TI: PenPan: A general tool for the attribution of changing pan evaporation
AU: * Farquhar, G D
EM: Graham.Farquhar@anu.edu.au
AF: The Australian National University, ACTON, Canberra, ACT 0200, Australia
AU: Hobbins, M T
EM: Michael.Hobbins@anu.edu.au
AF: The Australian National University, ACTON, Canberra, ACT 0200, Australia
AU: Roderick, M L
EM: Michael.Roderick@anu.edu.au
AF: The Australian National University, ACTON, Canberra, ACT 0200, Australia
AU: Rotstayn, L D
EM: Leon.Rotstayn@csiro.au
AF: CSIRO Marine and Atmospheric Research, Aspendale, Melbourne, VIC 3195, Australia
AB: Evaporative demand is routinely measured using the evaporation of water from standardised pans. The most common are Class A pans: they are metal dishes 4 feet in diameter and 10 inches deep sitting on a wooden platform. Because of the practical importance in agriculture and engineering, there is a wealth of pan evaporation data. Analysis has shown that in most places, pan evaporation has declined over the last 30 to 50 years despite the well documented increases in near–surface air temperature. It is important to understand why this has occurred. Using generic principles of mass and energy balance, we developed the PenPan model of evaporation from a class A pan for attribution purposes. In this talk we briefly describe the PenPan model and then demonstrate its application at 41 sites, broadly scattered across Australia, for the period 1975-2004. We found that the decline in Australian pan evaporation was mostly due to declining wind speed with some regional contributions from declining radiation. In general, the observed changes in vapour pressure deficit and air temperature were too small to have an appreciable impact on pan evaporation rates. By a comparative analysis, we show that the general global trends of declining evaporative demand are most due to various combination of declining radiation and/or wind.
DE: 1620 Climate dynamics (0429, 3309)
DE: 1813 Eco-hydrology
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
SC: Hydrology [H]
MN: 2007 Fall Meeting