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Title: IMPACT OF GLOBAL DIMMING AND BRIGHTENING ON REFERENCE EVAPORTRANSPIRATION OVER COMPLEX TERRAINS ESTIMATED FROM MINIMUM CLIMATOLOGICAL DATA

Author: G. Papaioannou, S. Athanasatos and G. Kitsara

Year: 2009

Publisher: European Water Resources Association (EWRA)

Description:

For climate trend studies or for use in climate models, in areas where time series of weather measurements are often available for more sites or for longer time periods only as monthly values, it is desirable to be able to use minimum monthly climatological data to estimate reference evapotranspiration, accurately. A new ‘reference evapotranspiration model for complex terrains’ (REMCT), with monthly time step, is used for estimating trends of reference evapotranspiration in Greece, incorporating rainfall occurrence, and air temperature and the effect of climate and site elevation. REMCT is applied after developing a methodology for calibrating its parameter values with monthly Penman-Monteith estimates obtained from daily values of the appropriate meteorological parameters, in 29 sites evenly distributed over Greece for the period 1974-2001. Furthermore in this study, trends in reference evapotranspiration based on REMCT are examined for 16, 22 or 29 stations across Greece, during the periods 1950-2001, 1958-2001 or 1986-2001, respectively. The consistency of the reported trends in radiation and temperature records and their implications for the hydrological cycle and especially the trends in the modelled reference evapotranspiration are investigated. Thus, the signs of trends in reference evapotranspiration are examined according to the global dimming or brightening periods, taking into account some of the studies suggesting that the widespread reduction of surface solar radiation (‘global dimming’) resulted in reduced  evaporative cooling at the land surface, (consistent with reported decreasing pan evaporation for many regions throughout the world, with widely different climates, over the past 50 years), was effective up to the 1980s and gradually transformed into ‘brightening’.