Temporal and spatial characteristics of pan evaporation trends and their attribution to meteorological drivers in the Three‐River Source Region, China

Abstract

Pan evaporation is an important indicator of atmospheric evaporative demand, and its long-term variation is of much concern in studies of climate change. Based on data from 33 meteorological stations from 1962 to 2012, this work considered the temporal and spatial trends of pan evaporation and the meteorological variables that affect them in the Three-River Source Region (TRSR) of southwestern China. Pan evaporation in the TRSR has decreased significantly since 1988 with an obvious abrupt change from 1993 to 2003. Furthermore, a 27 year period of oscillation has existed over the past 51 years. Pan evaporation reflects the combined effects of four meteorological variables: net radiation (R n ), wind speed (u 2 ), actual vapor pressure (e a ), and air temperature (T a ). Based on this research, a number of conclusions were drawn. (1) The pace of climate change increased after 1980 and pan evaporation decreased at a rate of À13.3 mm/a 2 from 1980 to 2012, which is much faster than the rate of À1.2 mm/a 2 from 1962 to 1979. (2) For the decrease of pan evaporation from 1980 to 2012, the quantifying contributions of R n , u 2 , e a , and T a were À8.7, À6.4, À1.8, and +3.6 mm/a 2 , respectively. Thus, it was established for the TRSR that "global dimming" was the main reason, and "wind stilling" was a close second to global dimming for the decrease in pan evaporation. (3) Different regions of the TRSR are affected differently by the effects of the meteorological variables. Low-elevation regions in the TRSR are more susceptible to the effects of net radiation and wind speed, whereas high-elevation regions are affected more by actual vapor pressure and air temperature.

Pan evaporation paradox and evaporative demand from the past to the future over China: a review

“…The annual change of E pan over China for the most recent period of 1960–2014 and the forcings are shown in Figure , and the spatial pattern of the periodical trends are shown in Figure . The annual E pan exhibits an obvious downward trend for 1960–1993 at about −2.60 mm/y 2 and then reverses upward from 1994 at 4.29 mm/y 2 over China (Figure ), showing strong evidence of the evaporation paradox for the period of 1960–1993, generally in line with worldwide observations . For the recent period of 1994–2014, the strong warming period, the E pan starts to go up.…”

“…The decline of potential evaporation trend has been well reported in China as well as at the regional scale, such as for the Tibetan Plateau, the Yangtze River Basin, the Yellow River Basin, the Hai River Basin, Northwest China, and Southwest China, while potential evaporation increased in some parts . Here, we use pan evaporation in China as a case study to interpret the pan evaporation paradox in the past and the projection for the future using state‐of‐the‐art climate models.…”

Changes in Pan Evaporation and Their Attribution to Climate Factors in the Zoige Alpine Wetland, the Eastern Edge of the Tibetan Plateau (1969–2014)

“…The decreasing u 2 and R n have resulted in the decline in E pan in the Tibetan Plateau in the past fifty years [16,23]. However, in the Zoige wetland, although decreasing wind speed (u 2 ) and net radiation (R n ) resulted in negative effects on E pan , the increasing water vapor pressure deficit (D) and temperature (T a ) resulted in the increasing trend in E pan during 1969-2014.…”

Reference evapotranspiration trends from 1980 to 2012 and their attribution to meteorological drivers in the three-river source region, China

“…Daily meteorological data were obtained from 33 stations in the TRSR from 1 January 1980 to 31 December 2012. The station information is presented in Table , and the geographical location of the stations is shown in Figure (Wang et al , ).…”

“…Roderick et al (2007) pioneered an approach for attributing the change of evaporative demand through a full physically based formulation of E pan . This differential equation method has been widely used to attribute the change in E pan (Donohue et al, 2010;Liu and McVicar, 2012;Wang et al, 2015) but is rarely used for ET 0 . Liu and Zhang (2013) proposed this method as appropriate for an attribution analysis to ET 0 .…”