The Study On The Calculation Of Irrigation Amount For Irrigation Event And Its Application In Local Area

Agriculture is the most basic and important part of human activities,which affects human's survival and development.Agricultural irrigation is a great contributor to food production,especially in those cultivated areas suffering from water shortages.At present,the irrigated land which accounts for 16%of total farm land produced about 30%-40%of crop in the world,and a third population's incomes is related to irrigation agriculture.Meanwhile,irrigation costs much fresh water every year,and about 2600 km3 of freshwater was withdrawed from surface water and groundwater in 2000.Nowadays,the irrigation water(Irrigation amount)accounts over 70%of total using water and even 90%of consumptive water.As one of the most important parameters in depicting human irrigation activity,irrigation amount is also crucial to crop yield estimation,hydrological process simulation and local climate changes.Therefore,an easy and effective method for acquiring irrigation amount is deserved to be studied.It has great significance to calculated irrigation amount and study the irrigation effect.The satellite equipped with various sensors can observe the land surface indistinguishably,and the remote sensing data can also well present the condition of land surface.In addition,the remote sensing data is characterized with the properties of multiple scales,easy accessibility and easy processing,which is considered as the most effective tool to acquire irrigation information.However,compared to the parameter extraction of irrigated areas,the extraction of irrigation amount by using the remote sensing made little progress.In the progress of calculating irrigation amount with remote sensing data,the relationship between remote sensing data and irrigation amount in irrigation period is needed to be modeled.So,irrigation timing is particularly crucial in this process.But the existing method based on remote sensing to acquire irrigation parameters can hardly extract irrigation timing.The scientific issue of this study is how to extract the irrigation timing of dryland cultivated areas by using remote sensing data,and how to model the relationship between remote sensing data and irrigation amount?The aim of this study is to provide a method that can calculate irrigation amount by using remote sensing data.Aimed at the above scientific issue,this study developed a method that can calculate irrigation amount for each irrigation event.With this method,the irrigation amount for a continuous area can be calculated by using remote sensing data.Firstly,three types L-band satellite-based soil moisture products are evaluated,and the product with highest accuracy is used to obtain the time series soil moisture data.Then,the increased stage of soil moisture was extracted out from the time series satellite-based soil moisture data,the fuzzy logic is used to infer the irrigation event that results in the increase of soil moisture.Finally,based on the soil water balance,a model for calculating irrigation amount was developed.This model can be used to calculate irrigation amount with the surface soil moisture.Adopting the method proposed in this study,the irrigation frequency and irrigation amount are calculated in different years in the study area of Henan Province.As the irrigation frequency maps show,the spatial pattern of all the frequency maps presents decreased trend from the south to the north,which is in contrast with the pattern of yearly rainfall,while similar with the pattern of yearly evapotranspiration.Such result proves that the irrigation frequency extracted with the method is reasonable.From the irrigation amount maps,these maps present similar spatial pattern distribution with that of irrigation frequency.Besides,the irrigation amount calculated in this study has a reasonable relevance with the difference of evapotranspiration and rainfall.For the irrigation amount in the study area(except for Xinyang City in the south of Henan Province),the calculated irrigation amount in this study is 5.18 billion m3 for 2016,while it is 6.35 billion m3 for 2017.The statistical data from the water resources bulletin show that the irrigation amount is 10 billion m3 for 2016 and 9.85 billion m3 for 2017.The bias between the calculated irrigation amount and statistical irrigation amount is 48.25%for 2016,and it is 35.48%for 2017.The method proposed in this study performs steadily in the small area.It should be noted that the statistical irrigation amount refers to the total water consumption for irrigation,while the calculated irrigation amount refers to the water poured to the land.This is the reason that a large difference exists between the statistical data and calculated data.In addition,compared with the existing method,the caculation method adopted in this paper has improved in the precision.It can be concluded that the method proposed in this study is available in calculating irrigation amount by using satellite-based soil moisture data.The calculated irrigation amount by the method proposed in this study can avoid the weakness of statistical irrigation data,which are poor real-time and unevenness in data quality.It also avoids the weakness that it cannot exactly present the irrigation time in the numerical simulation method.The method developed in this study further improves the extraction of irrigation parameters by using remote sensing data.The irrigation amount calculated in this study can provide irrigation parameter for simulating the influence of human irrigation activity on natural environment in the Community Earth System Model.