Abstract
The effects of meteorological factors on reference evapotranspiration (ET0) are variable on different time scales, although research tends to focus only on certain time scales. Therefore, using the meteorological data from 1958 to 2017 of Beijing, China, ET0 values over the last 60 years were calculated using Penman–Monteith method. The variation in ET0 values was thus analyzed against four meteorological factors over different time scales. The sensitivity of ET0 to these factors was assessed using a sensitivity coefficient, while the contribution of each factor to ET0 change was quantified by combining this sensitivity coefficient with the factor’s relative change rate over multiple time scales. The results showed that the sensitivity coefficient of relative humidity over different time scales were all negative, while the sensitivity coefficients of net radiation, temperature and wind speed were mostly positive. The main sensitivity factors of ET0 on different time scales varied. On annual time scales, the main factors were relative humidity and temperature. Over annual time scales, relative humidity and net radiation alternated as the main sensitivity factor; while over interannual time scales, the most sensitive factor was relative humidity during 1958–1979 and net radiation thereafter. The contribution of these four meteorological factors to ET0 also fluctuated greatly on intra-annual time scales. On daily time scales, the contributions of temperature and wind speed at the start and end of the year were large, while net radiation and relative humidity were dominant mid-year. On monthly to seasonal time scales, the contributions of these four meteorological factors to ET0 were notable. The contribution of relative humidity was largest in spring and autumn; net radiation was dominant in summer, while temperature and wind speed were dominant in winter. This research on the temporal variability of ET0 response factors is of great significance for understanding regional climate change.
Highlights
Evapotranspiration refers to the key hydrological process of water vapor escaping from the land surface to the atmosphere, which occurs between vegetation, soil or open water and the atmosphere [1,2]Reference evapotranspiration (ET0 ) is defined as the maximum evapotranspiration of a hypothetical underlying surface of green grass 0.12 m in height, actively growing and adequately watered, with fixed surface resistance and albedo values of 70 m/s and 0.23, respectively [3,4]
The contribution of relative humidity was largest in spring and autumn; net radiation was dominant in summer, while temperature and wind speed were dominant in winter
1.29–13.57 MJ/m2 /d, −3.65–26.48 ◦ C, 43.39%–75.25%, 1.30–2.31 m/s and 29.10–154.14 mm, with average values of 7.68 MJ/m2 /d, 12.45 ◦ C, 55.94%, 1.79 m/s and 87.92 mm, respectively, the changes in these four meteorological factors and ET0 were consistent with those observed at daily scales, with similar trends in RN, T, relative humidity (RH), U and ET0 (Figure 2)
Summary
Evapotranspiration refers to the key hydrological process of water vapor escaping from the land surface to the atmosphere, which occurs between vegetation, soil or open water and the atmosphere [1,2]Reference evapotranspiration (ET0 ) is defined as the maximum evapotranspiration of a hypothetical underlying surface of green grass 0.12 m in height, actively growing and adequately watered, with fixed surface resistance and albedo values of 70 m/s and 0.23, respectively [3,4]. To study the climate response of ET0 , various methods have been used, including principal component analysis, partial correlation analysis, sensitivity coefficient analysis and methods combining the sensitivity coefficients with the relative change rates to calculate the contribution of meteorological factors. Among these methods, the sensitivity coefficient method is the most widely used [22,23,24]. Others have suggested that T or RH were the most sensitive factors affecting
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