Evaluation of TerraClimate gridded data in investigating the changes of reference evapotranspiration in different climates of Iran

Abstract

Study region: Different climates in Iran, including the northwestern regions (cold), southern coasts (hot and humid) and central regions (hot and dry). Study focus: TerraClimate network data (5 km resolution) from the 40 years (1981–2020) was used to investigate changes in the trend and breaking point of the reference crop evapotranspiration (ETo) time series for different climates in Iran. Statistical assessment indices (RMSE, R2, and BIAS) were initially employed to assess network data accuracy with ground stations. The temporal-spatial alterations of the trend, the breaking point in ETo, and its extreme values were then investigated using Mann-Kendall, Sen's Slope, Pettitt, and Bayesian quantile regression tests. New hydrological insights for the region: The correlation coefficient between monthly gridded ETo data and ground data was calculated to be more than 0.95, with an average value of BIAS of –1.1. The average ETo in the studied climates had increased. The increasing tendency for high ETo values had the highest slopes in cold climates in winter (slope >70 %), hot/dry in spring and summer (slope 40 %), and hot/humid climates in summer and winter (slope 50 %). Additionally, the findings of Pettitt's test suggest that the three climates of Iran had a rising break point in the autumn and winter (cold), autumn and spring (hot/dry), and autumn (hot/humid) seasons, respectively. This indicates that rapid changes have been more common from 1996 to 2000.

Keywords

• Bayesian quantile regression
• Changepoint
• Evapotranspiration
• Spatial-temporal
• Trend