Publications

This study focuses on assessing trends of reference evapotranspiration (ET₀) considering aridity. Weather data sets of 54–62 years of Inner Mongolia, a Chinese Province where climate varies from hyper-arid in the West to wet sub-humid in the East, were used. Trends were analyzed for ET₀ computed with the FAO Penman-Monteith method (PM-ET₀) using full data sets of maximum and minimum temperature (T_max and T_min), sunshine duration (SD) used to compute net radiation, relative humidity (RH) and wind speed (WS). Trends were also assessed for ET₀ computed with the Hargreaves-Samani temperature eq. (ET_{0 HS}) and the Penman-Monteith equation with temperature estimates of solar radiation and actual vapour pressure (ET_{0 PMT}). In addition, trends relative to T_max, T_min, SD, RH and WS were assessed. Trends for PM-ET₀ show to vary with aridity, with decreasing trends in the areas marked by aridity in the West and increased trends in less arid and sub-humid areas in the East. The detected trends are well explained by the trends in weather variables which consist of large increasing trends of T_max and T_min and of decreasing trends for SD, RH and WS. Therefore, negative trends of ET₀ occur where impacts of increases in temperature and decreases in RH are smaller than impacts of declining SD and WS; otherwise, when warming influences are larger it results a positive trend for ET₀. Trends were coherent when considering seasonality influences. Contrarily, results for the temperature methods, ET_{0 PMT} and ET_{0 HS}, always identified increased trends for ET₀ due to warming effects. These results show that it is inappropriate to assess ET₀ trends when using simplified temperature methods.