Variation in Potential Evapotranspiration and Its Sensitivity Coefficients to Climatic Factors in the Huang-Huai-Hai Plain

Potential evapotranspiration (ET0) is generally accepted to be an important element of the hydrological cycle, and changes in sensitivity coefficients of ET0 are of great significance for agricultural water use planning, irrigation system design and management. Potential evapotranspiration and their sensitivity coefficients in four seasons and entire year were calculated by the Penman-Monteith methods and partial derivative equation across six agricultural sub-zones of the Huang-Huai-Hai plain (3H plain) from a data set of daily climate variables in 40 meteorological stations during the period from 1961 to 2013. The highest value of ET0 was found in summer, while in autumn and winter in the fourth zone. A decreasing trend for ET0 was detected in summer in these six sub-zones in recent 53 years and maximum amplitude was found in fifth zone. However, an increasing trend for ET0 was detected in second and sixth zone during spring and in second zone during winter. Relative humidity was considered to be the most sensitive variable for ET0 in spring, autumn, winter and whole year and solar radiation was the most sensitive variable for ET0 in summer. Moreover, the positive and negative values of sensitivity coefficients were recognized as solar radiation and relative humidity respectively for ET0 with a decreasing trend, similarly for wind speed and air temperature with an increasing trend. Moreover, the high value of sensitivity coefficients to relative humidity and wind speed was found in the first zone of study area, while the high value of sensitivity coefficients to solar radiation and air temperature was in fourth zone of south region. The findings from this research provide important information for crop planting adjustment, ecological engineering planning and water-soil resource management in 3H plain in an attempt to improving the healthy development of agriculture and ecological environmen