Assessment And Prediction Of Drought In Western Liaoning Province

Liaoning is a province with frequent flood and drought disasters characterized in high frequencies and huge losses.The precipitation in Liaoning Province is decreasing from southeast to northwest in which the precipitation of western Liaoning is the least with only 500 mm precipitation in the normal year.In other words,the water resource in western Liaoning is scarce because the frequency and severity of drought in western area are the highest in Liaoning Province.However,the basic research on drought in this area is relatively weak.To this end,this study carried out the analysis of the causes of drought in western Liaoning,the revision of the drought level standard in western Liaoning,the comprehensive evaluation method of multi-index numerical drought in western Liaoning,the study of drought time and spatial distribution in western Liaoning,the research on the prediction of drought trend and the research on agricultural drought countermeasures in western Liaoning.Additionally,the main research results are as follows:(1)According to the actual historical drought frequency,the various drought index standards in western Liaoning were revised,and the problem of applying the national drought level standard and the inaccurate evaluation of drought level in the western Liaoning region were solved.Moreover,based on that revised standard,a total of nine drought indicators were used to establish a drought indicator scale system in western Liaoning.First,meteorological drought indicators include rainfall anomaly percentage,Z index,SPI index and continuous rain-free day.Second,hydro-logical drought indicators include water intake anomaly percentage of rivers and water storage anomaly percentage of reservoirs.Next,soil relative humidity indicators and drought-affected percentage of crops are included in agricultural drought indicators.Last,social-economic drought indicator includes percentage of people who have difficulty with obtaining drinking water.(2)A comprehensive numerical evaluation method for drought in western Liaoning is proposed,which means the degree of drought level is numerically.In particular,the degrees from light drought to extreme drought are corresponding to number 1 to 4.In addition,the values of the drought levels of the four types of drought indicators are squared,averaged and extracted roots;as a result,comprehensive values of the drought level of the desired area are obtained.On the other hand,the results of typical drought verification are consistent with the actual situation of annual drought from the typical years.(3)The results of EOF demonstration shows that the first spatial variation indicates the variation of precipitations in the whole western Liaoning area are consistent within different regions.However,the second spatial variation represents more(less)rainfalls in the southeastern part of western Liaoning are correlated with less(more)rainfalls in the northwestern part of western Liaoning.Furthermore,the third spatial variation displays the pattern as more(less)rain in the eastern part is responded to less(more)rain in the western part with in western Liaoning area.The annual precipitation in western Liaoning has a quasi-periodic change of 5 years,9 to 11 years,23 years and 40 years.Also,Fuxin,Huludao and Jinzhou have the longest continuously rain-less days in spring and summer.Therefore,the patterns of drought occurrences in western Liaoning are obviously seasonal which have the highest frequency of drought in spring,the lowest frequency of drought in autumn,and the medium frequency of drought in summer.On the other hand,from the perspective of regional distribution,the drought frequencies in Chaoyang,Fuxin and Jinzhou areas are relatively high which have annual drought frequencies with 67.2%,60.7%and 55.7%,respectively.All cities of western Liaoning have patterns with continuously occurrences of drought,especially in Chaoyang and Fuxin areas.Indeed,the number of years of continuous drought in Chaoyang area is typically 4 to 7 years.Overall,the occurrences of drought and flooding are alternating between years and concurrently during the same year.In addition,the appearances of drought in various regions of western Liaoning have gradually increased from the year of 1949 to 2015.(4)The regression model of soil moisture is established in this paper.The accuracy of the forecasts depends largely on the accuracy of the forecasting scheme.Nevertheless,the accuracy of the forecasting scheme is based on sufficient and reliable soil moisture monitoring data.Therefore,it is necessary to collect as much information as possible when preparing the forecasting scheme of soil moisture.Additionally,it is extremely important to filter the data,especially the anomalous data.(5)In this paper,the causes of summer drought in western Liaoning are analyzed from different aspects,including factors such as atmospheric circulation,western Pacific subtropical high pressure,sea temperature and topographic.In particular,the large-scale circulation system in each layer of the troposphere results the appearance of drought in summers of western Liaoning.Moreover,the summer precipitation in Liaoning is even less with the control of the circulation system of 850 h Pa,500 h Pa and 200 h Pa layers.The early surrounding sea temperatures in different regions also have an impact on the summer drought in western Liaoning.For example,the corresponding correlation between the temperature of western Pacific sea area in April of the previous year and the summer rainfall in western Liaoning are extremely strong which indicates the impact on precipitation in western Liaoning from warm sea water is 10 years.As a result,it can be used as an important indicator to predicate summer precipitation in western Liaoning.Furthermore,the western Liaoning region is located in the middle transition zone between Inner Mongolia Plateau and Liaohe Plain,which makes the frontal weather system from the northwest to Huludao and Chaoyang areas sinking and diverging,and not conducive to the maintenance or formation of rainfalls.(6)Exploring the mid-term and long-term trends of summer precipitation in western Liaoning from astronomical factors,atmospheric circulation and sea surface temperature aspects.The results show that,(1)The sunspot index in December of the previous year has a certain level of effect on the summer precipitation in western Liaoning,and this research establishes the forecast correlation between these two variables.And in the forecast practice from 2016 to 2018,the pass rate is 2/3;(2)Analyzing the characteristics of the previous atmospheric circulation,which affects the summer precipitation in western Liaoning,so that the following three key areas of the 500 h Pa layer field are obtained.This result also has a certain indication on summer precipitation in western Liaoning;(3)The characteristics of previous sea surface temperature,which has an effect to the summer precipitation in western Liaoning,are analyzed.In addition,four of the essential areas of sea temperature zones are calculated,which definitely help predicate summer precipitation in western Liaoning.The forecast results of the past three years reveals,however,there is not a perfect forecast indicator that will forecast correctly for all three years.The reason may be that the precipitation in Liaoning province is influenced by many factors such as typhoon landing.Moreover,typhoon precipitation is difficult to predict,yet it has a significant impact on the precipitation pattern.