Abstract:Abstract: Accurate assessment of the temporal and spatial variation characteristics of the reference crop evapotranspiration in the main grain producing areas is of great significance to the optimal irrigation scheduling

irrigation system optimization

efficient use of farmland water and improvement of grain water productivity.Based on the daily meteorological data from 258 meteorological stations in main grain-production region

this paper calculated the Reference crop evapotranspiration from 1961 to 2013 by adopting Penman-Monteith formula

and analyzed the space-time variation during the 53 years by Sen’s+Mann-Kendall

Cumulative anomaly method and meteorological tendency rate.The results showed that:during the 53 years ET0 in main grain-production regions

Temperate humid and semi-humid area (I)

Temperate arid and semi-arid area (II)

Subtropical humid area (III) and Warm temperate semi-humid climate zone (IV) respectively were 901.90mm

741.89mm

1077.93mm

940.17mm (II>III>the whole region>IV>I);ET0 of the main crop growing season accounted for 87.58%

90.05%

85.11%

83.39% of the whole year

in the region and the various divisions;Except for IV(the tendency rate Y is 0.002mm/a ) ET0 in the whole region and I-III regions presented the decreasing trend during the 53years

the number of stations in downward was 171 accounting for 61.0％

the region slope decreased significantly and the trend variation was -0.288*mm/a（P<0.05）;The whole area and each district ET0 showed an increasing trend in 90s

the βwhole=4.993

Zwhole=1.978* (P<0.05)

the trend of increase is significant

other decadal trend decreases; ET0 high value areas mainly concentrated in the northwest of Sichuan and Inner Mongolia

low value areas mainly concentrated in the Sichuan basin and the eastern part of the northeast plain to the north part of the region ;ET0 showed degression from northwest to southeast with apparent regional difference

the stations showed the high value

med-high value

median and low value respectively accounted for 3.5%

12.4%

58.5%

25.6% of the whole stations; During the recent 53 years

the variation in trend of ET0 was greater within the year

ET0 showed an increasing trend from north to south in spring

but it was opposite in summer

then in autumn

ET0 in the major grain producing areas showed the tendency of low in central and high in north and south

compared with the autumn

ET0 had significant decline in winner

and it presented an overall downward trend by “North-South

West-East”

on main crops growing season

the ET0 decreased in the North China plain(declined significantly) and the central Northeast plain

and it had an increasing trend around the North plain and the lower reaches of Yangtze River region.