Farmland change induced land and water resource balance in Naoli River Basin from 1990 to 2013

Abstract: Since early 1990s, the agricultural structure of Naoli River Basin has been greatly adjusted with large amount of dry land changed into paddy field. This resulted in a set of problems in the utilization of water resources. To reveal the water profit and loss situation of the cultivated land resources in this river basin, the dynamic changes between the dry land and paddy field was analyzed and the farmland water requirements of the cultivated land in this basin was calculated in this article. By modeling the rice planting proportion coefficient which could show the structure of cultivated land, and using the contribution rate that was borrowed from the thought of economics, combing the results of established various types of crop, which was from the research of other scholars, the rate of paddy field and dry land proportion was determined. The remote sensing image data, the long-term sequenced meteorological data and the DEM data were used as its fundamental data resources in all the above analysis. By combining the planar climatic elements data which was attained from the dot data interpolation processing, the Penman-Monteith Model was used to create the computational condition of reference evapotranspiration (ET0) , which was generally agreed upon in the academic circles, the related model was used to analyze and compute the actual evapotranspiration (ET) for the condition of Naoli River basin, evaluation model of water profit and loss degree was established, and the order of evaluation standard was also structured to analyze the variation of area changes at different levels of moisture shortage. Fastly, the balance effect questions between the soil and water resources under the situation where the cultivated land constantly changed in the basin between 1990 and 2013 were discussed in this article. Results showed that the changes between the paddy field and the dry land in the Naoli River Basin were incredibly violent. The internal transformations between the paddy field and dry land were the primary changes. The dry land was the main source land for the increase of the paddy field; the farmland water requirements also increased from 541 mm in 1990 to 581.82 mm in 2013. These changes were mainly concentrated in the northwest and middle regions of this river basin and the range of the annual actual evapotranspiration was between 438-587 mm. Its overall distribution characteristic manifested itself as 'middle low, two ends high'; the change degree of the cultivated land's water profit and loss were obvious and the spatial distribution differences of the profit and loss index for evaluation grades were great. Except for the slight increase of the cultivated land with serious water shortage, the cultivated land area of the rest four evaluation grades all changed strongly. Among them, the area proportion of cultivated land with normal water shortage decreased 22.06% and the area proportions of cultivated land for the rest three evaluation grades all increased 4.74%, 9.61% and 7.72% successively. The above statement shows that the water deficit of the cultivated land in this river basin has been further intensified. These research results provide the references and consultancies for the farmland irrigation schemes in the Naoli River Basin.