Analysis of Changes in Reference Evapotranspiration, Pan Evaporation, and Actual Evapotranspiration and Their Influencing Factors in the North China Plain During 1998–2005

Abstract

Abstract Evapotranspiration (ET) plays an important role in both energy and water balances. Determining changes in the different types of ET and their influencing factors under climate change is crucial to fully understand the mechanisms controlling ET and regional water cycles. Based on ET and meteorological data measured during 1998–2005 at the Yucheng Comprehensive Experimental Station of the Chinese Academy of Sciences, the variation of reference ET (ET0), pan evaporation (Epan), and lysimeter ET (the actual ET, Elys) were estimated. Together with a Mann‐Kendall trend test, correlation and sensitivity analyses were conducted to determine the effects of climatic factors, crop coefficients (Kc), and leaf area index (LAI) on different types of ET. During 1998–2005, precipitation presented an upward trend at all time scales, and average temperature (Ta), minimum temperature (Tmin), relative humidity, Epan, and ET0 exhibited downward trends. Elys displayed a downward trend at the daily scale and an upward trend at monthly and annual scales. The correlation analysis indicated that Epan and Elys were significantly positively correlated with all climatic factors except precipitation and relative humidity. The sensitivity analysis revealed that except for relative humidity, the influence of the other climatic factors on ET0 was positive. The highest sensitivity was found for relative humidity, followed by Ta, maximum temperature (Tmax), and Tmin. An analysis of the influence of Kc and LAI on the actual ET indicated that with an increase of Kc and LAI, the actual water demand of crops also displayed an upward trend.

Keywords

• reference evapotranspiration, pan evaporation
• actual evapotranspiration
• North China Plain