SPATIAL-TEMPORAL VARIATIONS AND MUTATIONS OF POTENTIAL EVAPOTRANSPIRATION IN THE NORTHERN AND SOUTHERN REGIONS OF THE QINLING MOUNTAINS

Potential evapotranspiration(ET0),as an estimate of the evaporative demand of the atmosphere,has been widely discussed in researches on irrigation management,crop water demand and predictions in ungauged basins.Analysis of ET0spatial and temporal variation is the basic research on the impact of climate change on water resources,and also is important to the optimal allocation of agricultural water resources.In this study,based on the daily data from 54 meteorological stations in Northern and Southern Regions of the Qinling Mountains between 1960 and 2011,with the help of FAO Penman-Monteith formula,ET0 was calculated.By using the Spline interpolation method,climate trend rate,Pettitt abrupt change point detection,correlation analysis and other methods,we analyzed the distribution and temporal and spatial variation characteristics of ET0 as well as the meteorological elements which influenced evapotranspiration.The results are as follows.(1)Average annual ET0 was 964.2 mm,with the spatial distribution pattern of higher in east and lower in west.According to the size of evapotranspiration,the order was northern and southern region of the Qinling Mountain,the Han River Basin,the Ba-Wu Valley.ET0 in four seasons had the same distribution characteristics as the annual ET0,the order was summer,spring,autumn and winter.(2)According to the percent of stations with decreasing trend accounted for the whole stations,the order was the Han River Basin,southern slope of the Qinling Mountain,the Ba-Wu Valley,northern region of the Qinling Mountain.The decreasing trend was more obvious in southern region than that in northern region.ET0 of most stations in spring,which accounted for 78%,increased while ET0 in summer,which accounted 91%,decreased significantly.No obvious increasing or decreasing trend was founded in autumn or winter.The departure of ET0 in summer and annual between 1960s and 1970s was positive while negative between 1980s and 2000s;ET0 in autumn experienced negative and positive departure in the past 50 years,which appeared alternatively.ET0 in spring decreased in 1960s,then increased until 1980s,since then presented a downward trend,finally increased significantly in 2000s;ET0 in winter fluctuated in the past 50 years,the order was positive,positive,negative,positive and negative.The spatial and temporal distribution of ET0 illustrated the difference of ET0 in different latitude zone under the background of climate change.On the other hand,it could also be concluded that complicated terrain could influenced the distribution of temperature,precipitation,wind speed and other meteorological factors,which would finally influenced ET0.(3)The abrupt change of annual and spring ET0 happened in 1993 or between 1979 and 1981,while ET0 of 85% stations in summer changed in 1979.There was no obvious abrupt change points in autumn or winter.(4)Precipitation and ET0 of 70% stations in summer presented an negative correlation relationship,as for autumn the number accounted for 76%.Sunshine hour,maximum temperature,average temperature and wind speed correlated positively with ET0,which reached 0.01 significant level.According to size of correlation coefficient,the order was sunshine duration,maximum temperature,average temperature and wind speed.The decrease of sunshine duration and wind speed leaded to ET0 decreasing in summer and winter while temperature increasing caused ET0 increased in spring and autumn.