Spatiotemporal distribution of reference evapotranspiration in the Republic of Moldova

The main objectives of this study are to investigate the spatial distribution and changes in reference evapotranspiration (ET0) in the Republic of Moldova. Monthly data of maximum and minimum air temperature, sunshine duration, relative humidity, and wind speed recorded at 14 weather stations over a period of 52 years (1961-2012) were used. ET0 was computed based on the FAO Penman-Monteith formula. Annual and growing seasons of winter wheat and maize time series were analyzed for the 1981-2012 period as well as for the 1961-1980. The trends and their statistical significance in ET0 series were detected using Mann-Kendall test and T test, while the magnitude of the trends was estimated using Sen's slope and linear regression. For the 1981-2012 period, the results indicated that annual ET0 had a positive trend in more than 90 % of the time series according to both parametric and nonparametric methods. The magnitude of positive trends in annual ET0 series ranged between 13.80 and 72.07 mm/decade. In the growing seasons of winter wheat and maize, the results are similar to those found in the annual series. Significant decreasing trends dominated over the 1961-1980 period.