Abstract
Pan measurement is a reliable and efficient method for indicating the evaporative demand of the atmosphere. There are several types of pan evaporimeters worldwide, and the estimation of the conversion coefficients (Kp) between them is necessary in hydrologic research. In China, E601B pans were installed at all meteorological stations beginning in 1998. They replaced the 20 cm pans (φ20). To fully use the records from the two pans and obtain long-term pan evaporation, the spatial patterns of Kp between φ20 and E601B and the factors that influence Kp are investigated based on records from 573 national meteorological stations from 1998 to 2001. In this study, The results show that higher Kp values are found in southwestern regions and lower values are found in northeastern regions during the warm seasons (from May to September), while Kp values are lower during warm seasons than during cold seasons (from October to April the following year). In addition, net radiation was found to be the dominant climate factor that affects variations in Kp, followed by relative humidity and the vapor pressure deficit. This study can improve the benefit of not only the selection of appropriate evaporimeters by meteorological departments, but also of the study of temporal variability and trends in the evaporative demand.
Highlights
Evaporation is a key hydrological process [1]
The results show that the two pan evaporations exhibited the same spatial distribution (Figure 3a,b), while Kp exhibited significant spatial differences
This study presented the spatial distribution of Kp and investigated the dominant climatic factors
Summary
Evaporation is a key hydrological process [1]. It is an important nexus between the water cycle and energy budget and can further impact regional and global climate [2,3,4]. The evaporative demand of the atmosphere is controlled by radiative and aerodynamic factors, and it can be calculated using meteorological variables, such as radiation, wind speed, air temperature, and humidity [7,10]. These meteorological factors are not always available, especially radiation. Many types of pan evaporimeters have been installed in different countries to measure the evaporative demand [1,15], including Class A evaporimeters in the US and Australia [16], the GGI-3000 in Russia [17], the MO tank in Britain [18], and the 20 cm pan (φ20) and
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