Abstract
Pan evaporation decrease has been reported worldwide over them past
decades. A recovery trend, even an increasing pan evaporation trend, has
been recently found. Remarkably, most studies on Chinese pan evaporation
change in China were based on simulations involving meteorological
variables, including temperature, radiation (sunshine duration), wind
speed and relative humidity, due to the pan evaporation observation
inconsistency caused by the micropan (D20) replacement with large pans
(E601) around 2002. In addition, it has been reported that a large-scale
humidity sensor replacement across China has occurred since the 2000s,
which can cause an underestimation of relative humidity and in turn
leads to an inconsistency in simulated pan evaporation. Therefore, the
recent pan evaporation trend independent of the observed relative
humidity in China must be revisited. In this study, we complete the D20
pan evaporation from 1988 to 2017 according to E601 observations under
the constant conversion coefficient assumption between the evaporation
observations of these pans in the same month of every year at each
station and conduct trend and attribution analysis through linear
regression and PenPan-D20 model partial differential methods,
respectively. A significant 2.68 mm/a/a upward pan evaporation trend
(P<0.05) from 1988-2017 is revealed, primarily driven by the
air temperature rise across China. Humidity sensor replacement causes an
~1.3% relative humidity underestimation, producing
nonnegligible pan evaporation trend simulation errors.