"蒸发悖论"在秦岭南北地区的探讨

Abstract

Potential evapotranspiration(ET0),as an estimate of the evaporative demand of the atmosphere,it has been widely applied in irrigation management and predictions in ungauged basins.Analysis of ET0 spatial and temporal variation is the basic research on the impact of climate change on water resources,and is also important to the optimal allocation of agricultural water resources.In recent years,change trends in ET0 and its dominant factors across the different regions of the world have been studied by many researchers.Despite global warming,decreasing trends in ET0 have been detected in several countries including United States,Russia,India,China,Australia and New Zealand.Decreasing sunshine duration,declining wind speed and increasing relative humidity have been considered to be the main causes for the decreasing ET0.Northern and southern regions of the Qinling Mountains is far away from oceans,water shortage is a serious problem for agriculture in this area.So far,detailed investigation on the change trend in ET0 over this area has been lacking.In this study,based on the daily data from 47 meteorological stations in northern and southern regions of the Qinling Mountains between 1960 and 2011,ET0 was calculated by using FAO Penman-Monteith formula.We analyzed the change trend of ET0 and air temperature as well as the main factors affecting the decrease of ET0.It also discussed the existence of the evaporation paradox,the results are as following.(1)Air temperature of the whole region experienced two periods which increased initially and then decreased,1993 was abrupt change point.The decreasing rate between 1960 and 1993 as well as increasing rate between 1994 and 2011 both presented an pattern that declined from south to north,while increasing rate between 1960 and 2011 decreased from north to south.(2)1979 and 1993 were the change point of ET0,which divided ET0 into two periods,ET0 increased from 1960 to 1979 and then decreased from 1993 to 2011.Between 1960 and 1979,Evaporation paradox only existed in Han River Basin(HRB) and Bawu Valley(BWV),the periods of 1980—1993,1994—2011 and 1960—2011 all had Evaporation paradox phenomenon.Both the last 18 years and the whole 52 years in autumn as well as the initial 34 years and the whole 52 years in winter had Evaporation paradox phenomenon,which was more obvious in winter.(3)Precipitation decreased insignificantly in the past 52 years,and the precipitation and ET0 exhibited a contrary trend,which accounted 53% in the whole year and 79% in summer,respectively.The contrary trend between precipitation and ET0 was more obvious in summer than year scale.(4)According to the effect of meteorological elements change on ET0 change,the order was sunshine hours,wind speed,maximum temperature,relative humidity,mean temperature,mean air pressure and minimum temperature.On the year scale,the significant decrease of solar radiation(sunshine hours) was the dominating factor leading to the decrease of ET0.While on the seasonal scale,the dominating factor of spring′s ET0 was wind speed,the other three seasons were all solar radiation(sunshine hours).