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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-241
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
02 May 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Hydrology and Earth System Sciences (HESS).
Climatic controls on watershed reference evapotranspiration vary dramatically during the past 50 years in southern China
Mengsheng Qin1, Lu Hao1, Lei Sun1, Yongqiang Liu2, and Ge Sun3 1Key Laboratory of Meteorological Disaster, Ministry of Education (KLME)/Joint International Research Laboratory of Climate and Environment Change (ILCEC) /Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD) /Jiangsu Key Laboratory of Agricultural Meteorology, Nanjing University of Information Science & Technology, Nanjing 210044, China
2Center for Forest Disturbance Science, Southern Research Station, USDA Forest Service, Athens, GA 30602, USA
3Eastern Forest Environmental Threat Assessment Center, Southern Research Station, USDA Forest Service, Raleigh, NC 27606, USA
Abstract. Reference evapotranspiration (ETo) is an important hydrometeorological term widely used in water resource management, hydrological modeling, and understanding and projecting the hydrological effects of future climate change and land use change. Identifying the individual climatic controls on ETo helps better understand the processes of global climatic change impacts on local water resources and also simplify modeling efforts to predict actual evapotranspiration. We conducted a case study on the Qinhuai River Basin (QRB), a watershed dominated by a humid subtropical climate and mixed land uses in southern China. Long term (1961–2012) daily meteorological data at six weather stations across the watershed were used to estimate ETo by the FAO-56 Penman−Monteith model. The seasonal and annual trends of ETo were examined using the Mann−Kendall nonparametric test. The individual contributions from each meteorological variable were quantified by a detrending method. The results showed that basin-wide annual ETo had a decreasing trend during 1961–1987 due to decreased wind speed (WS), solar radiation (Rs), vapor pressure deficit (VPD), and increased relative humidity (RH). These variables had different magnitudes of contribution to the ETo trend in different seasons examined during 1961−1987. However, during 1988–2012, both seasonal and annual ETo showed an increasing trend, mainly due to increased VPD and decreased RH and, to lesser extent, to decreased absolute humidity (AH) and a rising air temperature. We show that the key climatic controls on ETo have dramatically shifted as a result of global climate change during the past five decades. Now the atmospheric demand, instead of air temperature alone, is a major control on ETo. Thus, we conclude that accurately predicting current and future ETo and hydrological change under a changing climate must consider changes in VPD (i.e., air humidity and temperature) in the study region. Water resource management in the study basin must consider the increasing trend of ETo to meet the associated increasing water demand for irrigation agriculture and domestic water uses.

Citation: Qin, M., Hao, L., Sun, L., Liu, Y., and Sun, G.: Climatic controls on watershed reference evapotranspiration vary dramatically during the past 50 years in southern China, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-241, in review, 2017.
Mengsheng Qin et al.
Mengsheng Qin et al.
Mengsheng Qin et al.

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Short summary
By identifying the individual climatic controls on reference ET (ETo) at a watershed level, we show that the key climate controls to ETo have dramatically shifted during the past five decades. Accurately predicting future ETo and hydrological change under a changing climate must consider changes in atmospheric demand (VPD). Our results have important implications for watershed management in paddy field-dominated humid regions, where actual water loss is mainly controlled by atmospheric demand.
By identifying the individual climatic controls on reference ET (ETo) at a watershed level, we...
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