Spatiotemporal changes and trend prediction of water surface evaporation in the north-south transitional zone of China
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Abstract:
With increasingly prominent global environmental problems,climate change research,including water surface evaporation,has become one of the current international scientific research hotspots and has received extensive attention from the international community.Northsouth transition zone is a sensitive area in response to global climate change,as well as the main water source for the midline of the SouthtoNorth Water Diversion and a key area for the western development.However,few researches focus on the water surface evaporation of the entire northsouth transition zone. The methods such as climate tendency rate,MannKendall (M-K) trend test and grey correlation analysis,as well as R/S analysis are mainly employed. The annual average water surface evaporation in China′s northsouth transition zone shows a significant upward trend,with a climate tendency rate of 19.3 mm/(10 a).There was an abrupt point in water surface evaporation around 1994.Before 1994,water surface evaporation showed a decreasing trend,with an annual average water surface evaporation of 807.5 mm.After that,water surface evaporation began to increase,showing an upward trend.From 1994 to 2017，the average water surface evaporation had increased by 50.0 mm compared with that from 1980 to 1993.Summer accounted for the highest water surface evaporation,followed by spring,autumn and winter.The climate tendency rates of each season were sorted by summer,spring,winter and autumn in terms of seasonal change trends,and the average water surface evaporation in summer showed a significant upward trend.The abrupt points occurred in each season were around 2004 in spring,around 1990 in summer,around 1985 in autumn,while there was no change in winter.Before the abrupt point,spring,summer and autumn all had a downward trend;after that,they all had an upward trend.There were obvious spatial differences in water surface evaporation in the northsouth transition zone,with the highest overall performance in the east,the second in the west and the lowest in the middle.The range of annual average water surface evaporation is 565.6 mm to 1 138.5 mm.Among them,the lowest annual average water surface evaporation was Dujiangyan,in the southwest of Sichuan Province,and the highest was Wudu in Gansu Province.The climate tendency rate of water surface evaporation was lower in the middle and northeast of the study area and was higher in the northwest,southwest and southeast.The lowest and highest values [JP2]were -54.0 mm/(10 a) at Sanmenxia Station and 66.1 mm/(10 a)[JP] at Songpan Station,respectively.The correlation between annual average water surface evaporation and various meteorological factors were analyzed.The order of correlation between each meteorological factor and water surface evaporation in the northsouth transition zone is sunshine hours,average temperature,average wind speed and relative humidity,respectively.Among them,the correlation between sunshine hour and water surface evaporation,and the correlation between average temperature and water surface evaporation are both greater than 0.8.However,the changing trend of sunshine hour in the northsouth transition zone was not prominent during the study period.Therefore,it can be concluded that the main reason for increasing water surface evaporation in the north-south transition zone is the increment of average temperature.The R/S analysis method was used to analyze the annual average water surface evaporation during the study period,and results showed that the water surface evaporation in the northsouth transition zone might continue the previous trend for a period of time.Therefore,it can be predicted that the water surface evaporation in the northsouth transition zone may continue to show an upward trend in the future. (1) From the perspective of temporal variation,the annual average water surface evaporation in the northsouth transition zone showed a significant upward trend,an abrupt point occurred around 1994,and the water surface evaporation increased significantly in summer.(2) From the perspective of spatial variation,the climatic tendency rate of water surface evaporation was lower in the middle and northeast of the study area,and higher in other areas.(3) The main reason for increasing water surface evaporation in the northsouth transition zone was the increase of average temperature.In the future,the water surface evaporation in the northsouth transition zone may continue to show an upward trend.
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