Impact of global dimming and brightening on reference evapotranspiration in Greece

Abstract

[1] In this study, the consistency of trends in radiation and temperature records and their implications for the hydrological cycle and especially the trends in reference evapotranspiration are examined during the period 1950–2001. The new reference evapotranspiration model for complex terrains (REMCT), with monthly time step, is used for estimating trends of reference evapotranspiration in Greece. REMCT is applied after developing a methodology for calibrating its parameter values with Penman-Monteith estimates. The calibrated REMCT estimates are independently validated against available pan evaporation measurements. The evolution of available sunshine duration anomalies measured in Athens during the period 1951–2001 are used for highlighting global dimming or brightening periods in Greece. The sign of trends in the modeled reference evapotranspiration and precipitation are examined according to the dimming or brightening periods 1950–1983 and 1958–1983 (for 16 and 22 stations, respectively) or 1983–2001 (for 16, 22, and 29 stations). The trends of REMCT estimates, precipitation, number of rainy days, and mean, maximum, and minimum air temperature for all sets of stations considered “as a whole” are evaluated during the same periods. The results show that the annual calibrated reference evapotranspiration trend shows a decline from 1950 until the early 1980s, followed by an upward trend until 2001, while the annual precipitation and rainy days indicate a downward trend during the whole period 1950–2001. The trends of mean, maximum, and minimum air temperature are found almost negligible during the dimming period and rather increased during the brightening period.