| Water-saving measures are an important human activity.Measures such as mountain reservoir construction in upstream reaches of a river,and use of seepage control and field drip irrigation techniques in middle and lower reaches,have advanced the efficiency of water and soil resources utilization,and significantly promoted the process of oasis expansion.However,large-area application of water-saving measures affects the water cycle factors such as soil moisture in the underlying surface,evaporation and infiltration.When changes occur to the character of the original water cycle,the evolution of ecosystems and the ecological environment are affected.Today,with the increasing attention on environmental change,water shortages and other global environmental problems,understanding the influence of water-saving measures on the water cycle clearly has great significance in understanding hydrological processes in arid areas,especially in a changing environment.Furthermore,an understanding of the relationship between water saving measures and hydrologic responses is helpful in accurately assessing the impact of human activities on ecological systems.In China,drip irrigation under mulched,water-saving technologies has been applied in the Manas River Basin for more than 20years,and the basin has become the largest oasis farming area in Xinjiang and the fourth largest agricultural irrigation district in China.However,the influence of water-saving technology on water cycle elements and water cycle processes has not yet been analyzed accurately and quantitatively.Rather,analyses of how water saving measures affect the water cycle are still qualitative and semi-quantitative.This article focuses on the simulation of hydrological processes under the influence of water-saving irrigation techniques.We analyze how water-saving technology influences water cycle factors such as precipitation,runoff,infiltration and evapotranspiration,and developa water cycle simulation model based on the large-area application of water saving measures.This paper extends previous related research from four aspects:analysis and summary of the present situation,description of how water cycle factors are influenced,development of a water cycle model,and verification and application of the model.The paper includes the following main content.(1)Present situation analysis and summary.Based on water and land resources development in the Manas River Basin,we analyze the influence of water resources development and utilization from artificial canals,as well as the water use structure and groundwater levels under water-saving technology.We analyze the development and utilization of land resources from the perspectives of irrigation area,planting structure,soil salinization,industrial structure and population scale under water-saving technology.Under the driving force of water-saving technology,the utilization efficiency of water and soil resources has been significantly improved in the Manas River Basin.The artificial oasis area has increased by 1.3 times,the annual growth rate of cultivated area has increased by 1.47 times,and the agricultural output growth rate has increased by3.9 times.It can be said that water-saving technology has effectively promoted the economic development and the oasis expansion process in the Manas River Basin,and promoted development of the regional economy.(2)Water cycle factors influenced by water saving measures.Using remote sensing images as a data source and combining these with field test results,we determine changes in the moisture regime of the underlying surface and how water cycle factors are influenced under water saving conditions.From this analysis,we estimate the parameters of runoff,infiltration and evaporation,and provide the necessary supporting parameters for developing a water cycle model.During the 20 years of water-saving technology extension,the land use dynamic degree of cultivated land and construction land was more active than previously.The area transferred from grassland to cultivated land was 1756.2km~2,and the area transferred from forest land to cultivated land was 567.4km~2.Loss of soil water was reduced by as much as 31.8%through mulching.The soil moisture content in the central plain has increased,but other areas have experienced more frequent drought.So,both the oasis and desertification processes have become more prominent under the influence of water saving technology.(3)Water cycle simulation model.We develop a water cycle model on the basis of water saving conditions and focus on the groundwater conversion process in oasis areas under the influence of water-saving measures.A runoff simulation model for mountainous areas and a groundwater numerical simulation model for oasis areas are established according to mountain and basin structure,respectively.The conceptual hydrological model MIKE11/NAM model is adopted for the mountain runoff simulation.The input parameters include meteorological data,flow data,river basin parameters and initial conditions.Visual-MODFLOW,a three-dimensional finite difference numerical simulation model,is adopted for numerical simulation of groundwater in oasis areas.The input parameters include meteorological data,precipitation parameters,infiltration parameters and evapotranspiration parameters.The results of the runoff simulation for mountainous areas are used as input to the groundwater numerical simulation model for the oasis areas.(4)Model verification and application.The innovative feature of the model is the introduction of different degrees of water gradient theory.We analyze the effects of water-saving irrigation on water cycle processes under traditional irrigation,conventional water-saving irrigation and efficient water-saving irrigation,and determine the groundwater balance and changes in groundwater depth under different irrigation methods.Lastly,we provide the basis for rational water resources development in the Manas River Basin.The main contributions and innovations encompassed in the research described in this paper can be summarized as follows:(1)The paper systematically analyzes and then summarizes the influence of water-saving technology on water and land resources exploitation in the Manas River Basin.The water-saving technology has promoted the oasis process and changes in the water cycle simultaneously.Using water-saving technology as the research background,the paper analyzes the impact of water conditions on water cycle factors in the Manas River Basin.(2)Based on remote sensing data in combination with field test results,we determined a set of technological processes that change soil moisture in theunderlying surface and influence other water cycle factors under water-saving conditions.We proposed water cycle simulation parameters such as runoff,infiltration and evaporation applicable underwater-saving conditions,and provided technical support for water cycle modeling in the Manas River Basin.(3)We developed a water cycle simulation model for application in water-saving conditions.A simulation model of mountain runoff and a groundwater numerical simulation for oasis areas we reestablished according to the physical characteristics of the Manas River Basin.The models innovatively incorporate gradient theory to describe different water-saving degrees.This innovation facilitated analyzing the effects of the traditional irrigation,conventional water-saving irrigation and efficient water-saving irrigation on water cycle process.From the simulations,we determined the water balance and the groundwater drawdown under different irrigation methods.The study results provide the basic data for rational water resources development in the Manas River Basin. |
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