Water Use Model In Farmland Shelterbelts System And Its Application In Huang-Huai-Hai Plain

Huang-Huai-Hai Plain grows a large portion of China's grain. Its farmland shelterbeltsserve crucial ecological protection for agricultural production, therefore, has been important incomprehensive agriculture development and revegetation of the area. However, sustaineddevelopments of agriculture and forestry are critically constrained by shortage of waterresource in the region. In order to address the increasing scarcity of water resources, climatechange and many other challenges, agricultural and forestry water consumptions must becoordinated in the development of Huang-Huai-Hai Plain farmland shelterbelts. Study of themulti-scale water usage relationships in the region, therefore, is of scientific significance.Interspecific water use had been an important research topic on the agroforestry system.Practical application of research findings, however, is often restricted by structure complexity,mode diversity, measure technology and simulation model limitations of the composite systems.This warrants a study of multi-scale water usage through synchronous measurement. By takingadvantages of ground-based observations and remote sensing observations in the spatial andtemporal scales, we can construct a model containing both precision and scale of star integrate,and using accurate ground-based observations of the data-driven remote sensing to get differentcomponents of the multi-scale evapotranspiration and water use efficiency data. Nowadays,researches about this model have not been publicly reported.In this study, the basin of Heilonggang located in Raoyang, Hebei Province has beenselected to demonstrate the model development for synchronization estimates of water usage inmulti-scale farmland shelterbelts. By using this model, Poplar and Wheat scale water usagerelationship had been analyzed from data collected in2007and April~June2008. Datacollected in1995are used to compare the water effect of two different age stage shelterbelts.The main results are as follows: Based on the basic principles of solar energy utilization efficiency and thePriestley-Taylor theory, a synchronous multi-scale model for various gross primaryproductivity and Evapotranspiration was developed. The model utilizes remote sensingobservations as primary, supplemented by conventional ground-based observations. WUEmodel can be obtained via dividing GPP by the ET. The spatial resolution of the model is30mand time resolution is8d.After the dynamic integration of MODIS and LANDSAT in the same wave band and time,the database of high temporal and spatial resolution remote sensing can be achieved.The wheat and tree shelterbelt ET and the wheat GPP can be used to verify the modelaccuracy. The results showed that there is a significant linear correlation between the simulatedand measured values. The correlation coefficient of measured and simulated values of wheatET is0.82with an average relative error of14.9%. The correlation coefficient of measured andsimulated values of poplar ET is0.833with an average relative error of15.62%. Thecorrelation coefficient of measured and simulated values of wheat GPP is0.927with anaverage relative error of15.62%. The correlations approve accuracy of the simulation model.The modelled results showed that the in the stage of winter wheat such as jointing-milkystage, Poplar shelterbelts evapotranspiration was slightly higher than winter wheat. Actually,each shelterbelt system of winter wheat was higher than forest. The RETs are3.37-8.18,3.66-7.20in2007and2008respectively. RET values of each grid are quite different, forexample the rate of variation (CV) in the10grid system tested in2007,2008are0.14and0.07respectively. These2years of10grids average RET were5.14and5.06, which are muchhigher than the forest on the actual area of crops evapotranspiration. In general, crops still themajor water consumer in farmland. Therefore it is feasible to develop poplar shelterbelts inHuang-Huai-Hai Plain.There are significant logarithmic or linear relationship between ET and GPP(P<0.05).This showed that water was one of determining factors of plant productivity. Though WUEdiffers among grids, general trend shows that grid crops have higher WUE than the forest. In poplar shelterbelts and Wheat system with forest age of12, soil moisture within10mdistance to the forest is lower than in CK, and the moisture beyond10m is higher than in CK.The border expands to15m if the forest age is doubled, Poplar shelterbelts can improve waterstorage in soil, but the effectiveness might fall as trees age., A comparison of CK in the wheatjointing-milking period shows that12a and24a forest age of shelterbelts can increase waterstorage capacity in0-200cm soil layer by7.8%and1.9%respectively. CK comparison alsoindicates that poplar shelter forests at above two ages can reduce wheat evapotranspiration upto19.1%and25.0%respectively. These results show that the effectiveness of fieldevapotranspiration does not decline with the ageing of shelterbelt significantly. This may helpto mitigate the farmland moisture reduction due to water intake by nearby tree roots.The analysis showed that trees at same age indifferent grid shelterbelts all contribute toreduce the volume of winter wheat evapotranspiration. During winter wheat jointing-milkystage, the average reduction of10test grid system are15.89ï¼…and16.73ï¼…in2007and2008,respectively. But the reduction rate differs greatly among different grids. The variations scalesbetween1.29%and36.08%in2007, between9.94ï¼…and23.58%in2008. The mutation rateswere up to0.56and0.13in2007and2008respectively.