Irrigation Schedule At Different Time Scales Under Random Rainfall

Crop irrigation system is the basic information for planning and designing of water-saving irrigation projects and management of irrigation area.The formulation of crop irrigation system is an important basis for compiling and implementing water use plans in irrigation areas.Typical year is selected on an annual scale when formulating crop irrigation schemes.Due to the insufficient consideration of the uneven distribution of rainfall,the rainfall resources cannot be fully utilized.For agricultural irrigation,Crop irrigation is a short-term water demand problem,and its water demand regulation cannot reach the annual regulation.The traditional method makes the uneven distribution of precipitation problem particularly prominent.In addition,rainfall is a random process,and whether rainfall will occur in the future is uncertain.The impact of global climate change on rainfall is becoming more and more evident.It is limited to use historical rainfall data only to develop irrigation schemes for crops in the next few years or even decades.In this paper,based on the meteorological data from 1951 to 2015 in Zhengzhou,Henan province,the frequency of annual rainfall,monthly rainfall,and ten-day rainfall were calculated respectively.And the rainfall distribution corresponding to typical years were analyzed under different probability of irrigation requirements.Then the typical years were selected at different time scales,and the rainfall of typical years under the same probability of irrigation requirement was compared and analyzed.Combining with the time scale,the rainfall prediction is carried out by using the Autoregressive Integrated Moving Average Model,and the irrigation schemes formulated therefrom are compared with the traditional irrigation schemes.The results showed that: 1)Selecting typical years on monthly and ten-day scales solves the problem of uneven distribution of rainfall to a certain extent,and improves the rainfall utilization during crop growth period.2)Under different time scales,there are differences in irrigation schemes of typical winter wheat-summer maize continuous cropping in Zhengzhou,Henan Province.With the decrease of time scale,the annual irrigation quota showed a downward trend,while the annual rainfall utilization showed an upward trend.3).The degree of deviation between the predicted and actual rainfall in 2015 is lower than that of the actual rainfall in 1989 and 2015.