| Recently,the continuous warming of environment has made it more uneven for the spatio-temporal characteristics of regional precipitation.In the meantime,extreme weather events have been more frequent,leading to undermining food security for the agriculture.In northwest China,although areas of the region and the per capita arable are large enough for us to exploit potential of agricultural resources,there is arid and semi-arid region.Therefore,in order to make better use of the agricultural resources,it is urgent for us to make it clear the northwest drought spatio-temporal characteristics,the spatio-temporal variations of the main crop water requirement.It is of great importance to cope with climate change,adjust agricultural structure and the reasonable allocation of water resources.The paper took Northwest China,Xinjiang,Qinghai,Gansu,Shaanxi,Ningxia and Inner Mongolia western region,as the research region.Based on the spatio-temporal characteristics of the region drought analysis,spatio-temporal features of meteorological factors and their influence on wheat and corn water requirement were researched.At the same time,the temporal and spatial variability of the wheat and corn net irrigation water requirement were analyzed.Through this paper,the main reults are as follows:(1)Five meteorological drought indicators were calculated,indicating that the standardized precipitation evapotranspiration index(SPEI)was the most suitable for the drought evaluation of the Northwest China,and the region could be divided into six subregions according to SPEI and make it clear of drought's spatio-temporal variations.The SPEI spatial analysis showed that the specific spatial distribution of different regions was slightly different for the SPEI climate trend rate on the annual and seasonal scales,but the overall distribution pattern from northwest to southeast was generally from wet to dry.The results of drought frequency at different degrees of SPEI showed that the overall frequency of drought was moderate>extreme>severe>light.The time analysis results of SPEI showed that,in the whole scope and partition scope analyzing drought changes,drought are characterized by a certain degree of fluctuations,but it can be found that they all become wet for the entire study period of drought,and drought intensity and drought station proportion showed different degrees of fluctuations.However,the results of Morlet wavelet analysis showed that,the trends of each region were inconsistent in recent years,and the dry and wet conditions in the future were also different in different cycles.(2)According to the analysis results of meteorological data,the spatial distribution of different meteorological factors are different.On the whole,the annual variation of all meteorological elements are similar in each region.The reference crop water requirement,average temperature,maximum temperature,minimum temperature and average wind speed show a single-peak pattern in the year,and the relative humidity and sunshine hours are slightly different in subregions.In terms of the interannual variation trend,the reference crop water requirement shows a decreasing trend in all subregions on the whole,and an increasing trend in recent years.The precipitation in each region recently showed a certain increasing trend.The average temperature,maximum temperature and minimum temperature showed an obvious increasing trend in each region.The average wind speed fluctuated in all areas,but decreased on the whole.The sunshine hours decreased in different degrees in each area.Hurst index analysis showed that,each meteorological element showed a certain degree of continuity in different study areas.For specific meteorological factors,the persistent trends were as follows: reference crop water requirement,precipitation,average temperature,maximum temperature and minimum temperature showed an upward trend;average relative humidity showed a downward trend;average wind speed and sunshine hours were slightly different in different regions.The results of the forecast model of the Mean Generation Function showed that the forecast quantity can basicallye xplain the change rule of meteorological factors,and each meteorological factor had the periodic change characteristic of different intension.(3)The relationship between meteorological elements and crop water demand was analyzed,and the main influencing factors were identified.Spearman Rank analysis results showed that,on the whole,the reference crop water requirement,average wind speed,average temperature,maximum temperature,minimum temperature and sunshine duration were positively correlated,while annual precipitation and average relative humidity were negatively correlated with crop water requirement.The results of grey correlation analysis showed that the first five meteorological factors affecting wheat water demand from large to small were the reference crop water requirement,maximum temperature,sunshine hours,average temperature and average wind speed.The first five meteorological factors that affected the water demand of maize from large to small were the reference crop water requirement,maximum temperature,average temperature,sunshine duration and minimum temperature.From subregional perspective,the top five meteorological factors affecting wheat water demand from large to small were reference crop water requirement,maximum temperature,sunshine duration,average temperature and average wind speed.The first five meteorological factors that affected the water demand of maize from large to small were the reference crop water requirement,maximum temperature,sunshine duration,average temperature and average relative humidity.(4)The spatio-temporal variability analysis of Crop water requirement and net irrigation water requirement in the northwest China showed that the annual average water requirement and net irrigation requirement of wheat and corn were decreasing year by year in the most parts,and there was obvious fluctuation of their time series.The annual average wheat water requirement from northwest to southeast was firstly increase then reduce,and annual average net irrigation requirement on the whole was of decresing trend from west to east and from north to south;On the whole,the annual average corn water demand was gradually decreasing from north to south,and the annual average net irrigation water demand was firstly increasing and then decreasing from northwest to southeast.According to the results of time series analysis,the crop water demand and net irrigation water demand in each subregion was of certain fluctuations.Combined with the Morlet wavelet analysis,it was found that both of them were periodic to some extent,and most of the first major cycles are basically between 45 and 62 years,but whose strongest main cycles are all under 56 years.The overall trend inspection on the water requirement and net irrigation water requirement of wheat and corn was in the trend of reducing year by year,except the water requirement of maize and net irrigation water requirement of wheat in ?subregion.According to the results of the forecast model of the Mean Generation Function,it could be found that the model could well simulate and predict the change of water demand and net irrigation water demand,indicating that their periodicity was strong.For the spatial distribution in typical hydrological years,the variation pattern basically was first increasing and then decreasing from northwest to southeast.With the decrease of wetness in a typical hydrological year,the crop water demand and net irrigation water demand become higher on the whole. |
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