| Affected by global climate change,the frequency of extreme weather events becoming more and more,resulting in the safe of water resources suffered a great challenge in China,especially irrigation water,immediately threaten to the country's food security.Baojixia Irrigation district is the largest irrigation districts in Shaanxi province.Agricultural production of Baojixia Irrigation district and the whole national economy and social development has played an extremely important role in Shaanxi Province.In this study,the Baojixia Irrigation district as the main object,considered the climate data,main crops,irrigation district agriculture development and other factors were affected on crop water requirenment.The impact factors of irrigated agriculture and the temporal and spatial variation of water requirement,as development of agricultural irrigation development planning under climate change conditions,determine a reasonable crop irrigation quota and cropping systems,and provide a reference for addressing climate change response measures.Through this study,the main results are as follows:? Due to climatic variation is random,and the volatility fluctuations,so this paper calculates the average value of each meteorological factors based on time series data,to eliminate the effects of fluctuations in the random factors,and to show and forecast trends meteorological factors.According to geographical location and meteorological data of 12 meteorological stations in Baojixia Irrigation district,and calculated data of the main crop growing period between 1961 and 2010,including the average temperature,the maximum temperature,minimum temperature,temperature and wind speed level,the average relative humidity,sunshine and precipitation.It was used time series analysis method to explore the evolution of various meteorological factors in Baojixia Irrigation district.The results shown: the average temperature,the maximum temperature and minimum temperature of Baojixia irrigated area in 50 years overall showed volatility on the rise,and the maximum and minimum temperaturefrom 1985 showed significant warming effect stately.Although showing frequent volatility in Baojixia Irrigation district of the average precipitation irrigation and standardized precipitation index(SPI)in time series,but time series of rainfall with SPI on the overall downward trend,and the extents of the past 20 years more and more irrigation meteorological drought seriously.The frequencies of drought were occurrence more and more,which resulting in the trend of warm and dry in Baojixia Irrigation district.In addition,the cyclical changes of relative humidity,wind speed and sunshine on a long time scale is not obvious differences.In addition,hurst exponent analysis method and wavelet analysis method also showed that: the average temperature,maximum temperature,minimum temperature and relative humidity of irrigation district were shown increased trends,while wind,sunshine hours,precipitation and SPI were shown decline trends.After a comprehensive analysis of the results of different research methods,the future of meteorological factors of Baojixia irrigation district in the future for a long time,the direction of change will be warmer and drier.?Calculated within each meteorological site of Baojixia all major crops for many years and the average annual water demand change from year trend analysis on the time scale.The results shown: Cotton is the main crop in the four largest crop water demand,from 1961 to2010 annual average water demand of cotton reached 626.34 mm/a,the average daily water demand in the years between 1.53~4.70 mm/d;followed by canola,water demand is 574.38mm/a,for many years the average daily water demand between 0.84~3.00 mm/d;water demand of summer corn is smaller,for 468.61 mm/a,for many years the average daily water demand between 3.20~5.03 mm/d;The minimum water requirement of winter wheat,is447.32 mm/a,the average daily water demand in the years between 0.89~3.08 mm/d.Meanwhile,the analysis of the variation of irrigated crops in different growth period corresponding to the frequency of different hydrological year water demand.The 12 sites in Baojixia irrigation district water requirement of different crops growth period from 1960 to 2010 were analyzed based on the spatial scale.The maximum and minimum average years winter wheat irrigation water demand of Xianyang station and Xingping station are reach 539.32 mm/a and 466.76 mm/a,separately.The maximum and minimum average years summer corn irrigation water demand of Xianyang station and Fufeng station are reach 520.59 mm/a and 461.09 mm/a,separately.The maximum and minimum average years summer cotton irrigation water demand of Xianyang station and Xingping station are reach 694.85 mm/a and 417.60 mm/a,separately.The maximum and minimum average years rape water demand of Xianyang station and Xingping station are reach 610.05 mm/a and 530.94 mm/a,separately.?Considered the spatial variability of crops irrigated water demand on the surface scale of the Baojixia irrigation district,this paper through the representatives crops water demand data of 12 meteorological stations to estimate irrigated water demand distribution with spatial interpolation methods,and to obtain 25%,50%,75% three hydrologic years for major crops of spatial distribution irrigated water requirement on the entire Baojixia irrigation district scale.There were shown basically similar trends that water requirement spatial distribution trends of four crops(winter wheat,summer maize,cotton and canola)in Baojixia irrigation district.Overall,water requirement of different crops illustrated increased trends but somewhere decreased from west to east;and showed slight increased gradually features whole reduced in local from the north to the south.In different hydrologic years and crop types for the 12 meteorological stations,the water requirement showed too higher at the northern stations of Qianxian,Liquan and east station of Xianyang,and too lower at the mid-south stations of Fufeng and Xingping in Baojixia irrigation district.? Previous studies on the impact of meteorological elements on the crop water requirements,and mostly used method of the correlation analysis;in fact,there have relationships between the different meteorological elements,which certain impact on the crop water requirements results.In this paper,the method of path analysis was used to analyze the impact of various meteorological factors on crop water requirements of Baojixia irrigation district,as well as to reveal the relative importance of various meteorological factors to affect the crops water requirement,and to analyze the limiting meteorological factors of crops water requirement.The results showed that: the main factors affected irrigation crop water requirements were the wind speed,sunshine hours,relative humidity,air temperature and the highest average temperature,and the absolute value of its decision-making coefficient were more than 10% in Baojixia irrigation district.The main limiting factors for winter wheat,summer maize,cotton and canola were minimum temperature,maximum temperature,minimum temperature and maximum temperature,separately;since the decision-making coefficient of the combined effects on water requirement of each crop were-5.42%,-10.99%,-4.53% and-14.35%,separately.?In this study,the method of the regression analysis was used to analyze the influence of meteorological factors on the net irrigation water demand of Baojixia Irrigation district.The results found: In winter wheat growth period,there were positive correlation relationships for the net irrigation water demand and the average temperature,sunshine and the maximum temperature,separately;and negative correlation relationships between the net irrigation water demand and the relative humidity,and precipitation,separately.During summer corn growing stage,positive correlation relationships for the net irrigation water demand and meantemperature,maximum temperature,sunshine hours the average temperature,separately;and negative correlation relationships between the net irrigation water demand and the relative humidity,and precipitation,separately.Average temperature,sunshine hours,relative humidity,the larger the maximum temperature,wind speed and precipitation were significantly affected water requirement of cotton.Positive correlation relationships for the net irrigation water demand of cotton and mean temperature,maximum temperature,sunshine hours the average temperature,separately;and a significant negative correlation relationships between SPI and cotton irrigation requirement.Positive correlation relationships for the net irrigation water demand of canola and mean temperature,maximum temperature,sunshine hours the average temperature,separately;and negative correlation relationships between the net irrigation water demand and the relative humidity,and precipitation,separately.?Considered the major features of crops planting structural and crops irrigated acreage,natural and economic conditions and crop requirements in Baojixia Irrigation district,etc;in this study,we referred to the current formulas to calculate the potential capacity of water-saving under different climatic conditions in Baojixia Irrigation district.In wet year,the main crops had the largest water saving potential,the water saving potential of winter wheat and summer corn were 78.93 mm and 122.72 mm,respectively;In median water year,water saving potential of crops was relatively smaller than that in wet year,the water saving potential of winter wheat,summer corn,cotton and rape were 40.96 mm,105.93 mm,125.01 mm and 70.6mm,respectively;In drought year,the water saving potential of winter wheat,summer corn and rape were all zero,cotton was 24.10 mm.Overall,Baojixia Irrigation district in wet year has greater water saving potential,water saving potential had close relationship with the year type and the crops as well. |
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