Revisiting Pan Evaporation Trends in Australia a Decade on

Abstract

Decreases in pan evaporation (Epan) have been reported around the world despite increasing air temperatures; this was attributed to reductions in wind speed and solar radiation. Using 42 years (1975–2016) of Australian Epan data, we reexamined Epan trends, adding over a decade of observations to previous analyses. Flexible local linear regression models showed that many previously reported decreasing Epan trends have plateaued or reversed. Attribution analysis confirmed that 1975–1994 Epan decreases in southern/western Australia were chiefly driven by decreasing wind speeds. Increasing vapor pressure deficit subsequently became dominant, resulting in 1994–2016 Epan increases. Climate trend analyses should consider applying flexible statistical models to qualitatively understand temporal dynamics, complementing linear models that are able to provide quantitative assessments, especially when multiple drivers are involved.