Seasonal Dynamics of Inter-Device Discrepancies and Their Key Influencing Factors in Monitoring Water Surface Evaporation

Accurate comparison of water-surface evaporation observations from different devices is essential for integrating long-term hydrological records. This study analyzed two years of synchronous daily observations from five co-located evaporation devices in Duyun, Guizhou, China: D20, E601, and three evaporation ponds with surface areas of 1, 5, and 20 m2 (P1, P5, and P20). Evaporation differences, conversion coefficients, correlations, and statistical variability were evaluated at annual, seasonal, monthly, and daily scales. The main findings were as follows: (1) among the three similarly constructed ponds, annual evaporation decreased from 946 mm for P1 to 896 mm for P5 and 874 mm for P20, whereas the annual totals measured by D20 and E601 were 842 and 861 mm, respectively; (2) the relationship among the three ponds varied within the year, reversing in July and August and becoming non-monotonic in May and June; (3) pairwise correlations were generally strongest in summer and weakest in winter, indicating pronounced seasonal variation in inter-device relationships; and (4) because D20 was installed above ground whereas E601 and the three ponds were buried, differences among all five devices reflected combined scale- and design-related effects, while comparisons among the three ponds primarily represented surface-area-related effects. These findings provide a site-specific basis for harmonizing evaporation records and improving their application in hydrological and water-balance studies.