Spatial and temporal variations of reference crop evapotranspiration and its influencing factors in the North China plain

Abstract

Potential evapotranspiration is the theoretical upper limit value of actual evapotranspiration, which constitutes the important parameters for the research of regional thermal balance, water budget, water resources assessment and crop water requirements. Study on regional response of potential evapotranspiration to global climatic changes in China has significance in global hydrological cycling, energy balance and eco-environmental evolution research. Reference crop evapotranspiration (ET0) as a common parameter is largely an evolution of definition of potential evapotranspiration and with the method of Penman-Monteith Model recommended by Food and Agriculture Organization for computing crop water requirements in 1998, reference crop evapotranspiration could be estimated quickly and accurately. Based on the daily observation data of the 56 meteorological stations in the North China Plain from 1960 to 2012, reference crop evapotranspiration were calculated, then the spatial-temporal variation patterns of reference crop evapotranspiration over North China Plain was analyzed with the methods of linear regression, spline interpolation and accumulative anomaly method. In the meantime, the dominant factors of the ET0’s variations in North China Plain were quantitatively analyzed by calculating sensitivity coefficients of reference crop evapotranspiration to climate elements and the relative change of the climate elements. The result showed that: (1) Annual reference crop evapotranspiration of north China plain was 1071. 37mm and the spatial distribution pattern was high center alternating with low center. The high value reference crop evapotranspiration areas mainly distributed in the northern Hebei, central part of Shandong mountainous region and western regions of Henan, while the low value centers distributed in the eastern regions of Hebei, southern Shandong, eastern and southern regions of Henan province. (2) The reference crop evapotranspiration has decreased obviously in North China Plain during the last 53 years by the rate of 12.8mm/10a, and its decadal variation showed that the decade anomaly consistently decreased. From the perspective of the regional distribution of ET0 change, the ET0 of the northern Shandong Peninsular and the northern regions of Hebei province showed a slowly increasing trend, while the ET0 of the rest areas decreased. (3) The sensitivity coefficients of reference crop evapotranspiration to the daily temperature (SAT), sunshine hours (SSH), wind speed (SWS) were positive values, while the sensitivities coefficients of reference crop evapotranspiration increased slowly, while SRH and SWS decreased. There was a corresponding relationship for the sensitivity coefficients of reference crop evapotranspiration, which meand areas of high sensitivity to temperature and wind speed had relative low sensitivity to sunshine hour and the relative humidity. (4) The dominant factors of ET0 in North China Plain were as follows:sunshine hours and wind speed were the dominant factors caused change of ET0 in North China Plain, while relative humidity, daily maximum temperature and minimum temperature contributed less to the change of ET0. Sunshine hours was the determining factor in the change of ET0 in many regions of the northern and the central regions of Hebei province, Bashang District of Hebei Province, the southern and western region of Henan province and the central regions of Shandong province.The regions affected by wind speed expanded across the Southern region of Hebei province, southern Henan Province and the north of the Yellow River in Henan Province, the central regions of Henan province, northwestern regions of Shandong province. The meteorological stations affected by temperature scattered in the west of northern Henan Province, western region of Henan province and Shandong peninsula, while relative humidity only had significant influence on the ET0 of the southern regions of Shandong province and Shandong peninsula.