Estimation Of Regional Crop Water Requirements And Development Of Management System

Crop water requirement is indispensable basic data for the evaluation of agricultural efficient water use and irrigation management in irrigation district.Due to the limitation of scientific cognition,financial capacity,time and energy,etc.,crop water requirement can only be measured on discrete or a comparatively small scale.Accordingly,there exists a great difficulty in estimating the regional crop water requirement.Besides,the current weather forecasting is quite precise with the development of the mainframe computer and numeral forecasting model.Therefore,how to enhance the estimation precision of the regional crop water requirement by utilizing the precise weather forecasting information has been a vexing problem for the irrigation management department.Aiming at the main problems in the regional crop water requirement estimation and the need of the irrigation management department,a systematic study on the scale conversion of crop water requirement,the estimation of the regional crop water requirement based on the weather forecasting information and the development of crop water requirement management system based on the WebGIS was carried out.The research findings include:1.An estimation method for the space distribution of crop water requirement was proposed based on the Principal Component Analysis(PCA)and Geographically Weighted Regression(GWR).By considering the impact of the macro terrain factor,the micro terrain factor,and the meteorological factor on the crop water requirement,as well as combining the PCA that effectively eliminating the collinearity of impact factors with the GWR which better explaining the spatial difference of the crop water requirement,an estimation method for the spatial distribution of crop water requirement was proposed based on PCA and GWR.This method can effectively reveal the influence of the affecting factors in different spatial locations on the crop water requirement and provide more detailed information on the region where the affecting factors suddenly change.Therefore,it is an instructive significance for the estimation of the regional crop water requirement.2.A method for multi-source information integration of crop water requirement was put forward based on prior knowledge.Based on the fact that the information on crop water requirement comes from many sources,and by using the measured crop water requirement as hard data,taking the literature data,the historical data in the irrigation experiment database,the calculation data from the meteorological information and remote sensing data as soft data,the expression methods of all the soft data and probability density function were explored and the prior probability density function was constructed by employing the maximum entropy.Then the prior probability distribution function was modified according to the Bayesian conditional probability formula and the posterior probability distribution function was obtained so as to realize the multi-source information integration of the crop water requirement.This method,by taking into account the historical data and prior knowledge like the experience of the experts,can greatly enhance the precision of estimating the regional crop water requirement where the sites are sparse and provide a new way to utilize the crop water requirement information from different sources.3.The heterogeneity of the spatial distribution of the winter wheat water requirement in North China was explained.The spatial heterogeneity of winter wheat water requirement on the overall,local situation and different scales in North China was analyzed using Moran's I method.The findings showed that the water requirement of winter wheat in North China had a significant autocorrelation at 1% significance level and that the winter wheat water requirement in the northern part of Henan Province and the middle and northern part of Hebei Province had also a strong autocorrelation.In the north south direction and the south east-north west direction,the water requirement of winter wheat had strong spatial autocorrelation under the scale of 400 km.The preliminary results indicated that the distance between the monitoring sites in two directions could be enlarged.The average scale of the water requirement for winter wheat in the north south direction approximated 430 km and the spatial autocorrelation in the west east direction was weak.4.The method for ascertaining the scale turning point of the crop water requirement was improved.Drawing upon the spatial structure of the irrigation experimental station network and the scale turning point of the remote sensing image,this study took the average local variance of the crop water requirement in the whole range of the studied region as the extent of measuring the deviation average.The smaller of the space granularity in sampling,the smaller of the change in crop water requirement,thus the local variance was low.In addition,the change of the crop water requirement and the local variance would increase with the increase of the space granularity in sampling.When the space granularity in sampling scale reaches a certain degree,it could be the average of many smaller sampling scales and the local variance value could be decreased.The method to determine the scale turning point was proposed by studying the change of the local deviation average in the range with the change of space granularity.5.The dominant factor that affects the crop water requirement on different scales was ascertained.Based the changing characteristic of the crop water requirement in the studied range,the dominant factors affecting the crop water requirement of the typical sites,the winter wheat region in North China and different space granularity were analyzed and determined by adopting the particular analysis,principal component analysis and partial correlation analysis.The results showed that the sunshine hours and the highest temperature were the dominant factors that affected the winter wheat water requirement in Henan Province.The next affecting factor was wind speed.Speaking from the winter wheat in the whole North China,the dominant factors that affected the crop water requirement included the thermodynamic factor,moisture factor and the dynamic factor.The micro terrain factor affected the crop water requirement in some degree.Sunshine hours was also a dominant factor affecting the winter wheat water requirement in different space granularity.6.A typical expression method for laying out the monitoring station network of the crop water requirement was proposed.By combining classical statistics and space statistics,a method for laying out the monitoring station network of the crop water requirement and the main procedure were put forward and the layout scheme of the monitoring stations for the winter wheat water requirement in North China under different monitoring precision was determined.Since the entropy of information could reveal the change of the crop water requirement in certain range,the entropy of the gradient in the studied region,relative elevation,the soil type and the land use was respectively calculated by employing the neighborhood analysis function of Arcgis expansion module.After calculating the comprehensive entropy of the entropies of the above affecting factors by using different weight,this study took the reciprocal of the comprehensive entropy as the weight of the weighting voronoi graphics.Then a typical expression method for the monitoring stations of the crop water requirement was put forward based on the entropy of information and the weighting voronoi graphics.7.A scaling method for the crop water requirement was put forward based on station site measurement and remote sensing.Though the site monitoring data are precise,it takes much time and energy to obtain them.And it is difficult to monitor data in large space range.Remote sensing can obtain basic information in large range more conveniently and quickly,but the measurement is not so precise.In order to make full use of the space advantage of remote sensing data and the precision of the site data,a method for the scale conversion and the realizable technological frame of crop water requirement information from one point to a whole area were proposed based on the crop water requirement of the site monitoring by combining the spatial variability information of the crop water requirement obtained from remote sensing data.8.An estimation technological system of the crop water requirement was constructed based on the weather forecasting information.As many parameters were often needed by the P-M equation recommended by FA0 56 and it would be harder to get those parameters.In order to make full use of the precise weather forecasting information,all the ETO estimation methods based on temperature were screened out firstly.And then related parameters of selected equations were corrected and a graph of the spatial distribution of the main parameters in North China was drawn.Finally,crop coefficient models based on accumulated temperature at different growing stages were established by coupling the accumulated temperature and leaf area index,and coupling leaf area index and crop coefficient.A forecasting method for the crop water requirement based on the weather forecasting information and an irrigation warning technological system were constructed and its forecasting precision was above 80% by actual measurement proves.9.A management and query system of the crop water requirement was developed based on the WEBGIS.This system combined the crop water requirement estimation,crop information query and the spatial distribution of crop water requirement.It made full use of display operation,analysis operation,data access operation,space object operation and output operation provided by Super IS.net.Compared with the traditional thin client GIS,the extendibility and space analysis of this system was stronger.Besides,this system could not only do attribute query and click query,but also do range query by using the mouse.It thus makes query more convenient and fast.By organically combining many new theories and new methods and addressing the main problems in regional crop water requirement estimation and the need of irrigation management,an estimation method for regional crop water requirement was put forward,a technological system of crop water requirement estimation based on weather forecasting information was constructed and a management and query system of crop water requirement based on WEBGIS was developed.This study provides effective theoretical and technological support for the planning design and management of irrigation project.However,there still exist some problems and deficiencies in this study due to the complexity of regional crop water requirement estimation and irrigation management.Therefore,more related studies need to be conducted in the future.