Characterization Of Climate Factors And Prediction Of Runoff In The Pearl River Basin

The Pearl River Basin is the third largest river basin in China,and the area through which it flows is the Pearl River Delta region,which is a very prosperous economic and cultural development in China.In recent years,the Pearl River Basin has experienced drought,reduced precipitation,and insufficient reservoir storage,etc.Therefore,we study the changing characteristics and spatial distribution of climate factors in the Pearl River Basin to reveal the correlation between climate factors and runoff,as well as to predict future runoff.It can provide some protection to the ecological environment of the Pearl River basin and some guarantee to the development of the Pearl River Delta region.This paper takes the Pearl River basin as the research object,using precipitation and temperature data from 42 meteorological stations in the basin from 1965 to 2019,using meteorological tendency,sliding mean,coefficient of variation and wavelet transform to determine the trend and periodicity of temperature and precipitation,and using spatial interpolation method to analyze the spatial variation of precipitation and temperature in the Pearl River basin.The monthly runoff of Dongjiang,Beijiang and Xijiang rivers are used to analyze the trend,abrupt change and periodicity of runoff.Cross wavelet was used to analyze the relationship between precipitation,air temperature and runoff.SARIMA and NAR models,as well as a combined model SARIMA-NAR model,were developed to simulate and predict the monthly runoff of Dongjiang,Xijiang,and Beijiang rivers.The results of the study are as follows:The annual and seasonal average temperatures in the Pearl River basin are in an upward trend,and the interannual average average temperatures show a stepwise upward trend,and the climate tendency rate shows that the warming in autumn is the highest,with a warming rate of0.024°C/10 a,and the slowest in summer,with a warming rate of 0.014°C/10 a.The seasonal interdecadal changes are: the temperature in spring decreases and then rises,and the remaining three seasons show a stepwise The upward trend.In terms of the coefficient of variation,the most drastic changes in winter temperatures are observed.The main cycle of annual and seasonal temperatures is around 28 a,and there are seven oscillations on the time scale of 20a-30 a.The summer temperature changes drastically after the abrupt change than before the abrupt change,and the annual,spring,autumn and winter mean temperatures change drastically before the abrupt change than after the abrupt change.Among them,the average winter temperature changes most drastically.Spatially,the annual and seasonal average temperature of the whole basin is in an upward trend,and the spatial variation of annual and seasonal average temperature gradually increases from northwest to southeast,with the highest temperature in Xuwen and the lowest temperature in Xianning except for winter in Anshun.The annual,spring,summer and winter average temperatures increase at the greatest rate in Yuxi and Shantou.The rate of temperature increase was greater in the east than in the west.The annual precipitation in the Pearl River basin showed a decreasing trend,but the change was not significant.The variation pattern of precipitation per 10 a in spring,autumn and winter is rising first and then falling,and the most drastic change of precipitation in winter is seen from the coefficient of variation.The first main cycles of annual and seasonal precipitation are 28 a,14a,29 a,15a and 16 a,and there are more than 7 oscillations in the time scale.The sudden fluctuations of annual and seasonal precipitation in the Pearl River basin are relatively large,and there are more years of sudden changes,and the trend changes of annual and seasonal precipitation after sudden changes are not significant.From the spatial analysis of precipitation,the distribution of annual,spring and winter precipitation is more regular,from west to east as first increasing and then decreasing.The spatial distribution of precipitation in summer and autumn is irregular.The maximum precipitation of annual and four seasons is located in Shaoguan,Huilai,Xuwen,Chenzhou and Shaoguan,and the minimum precipitation is located in Anshun.Among them,Gao is the place where the annual,spring and summer rainfall increases at the fastest rate,and winter precipitation shows an increasing rate in the whole basin.The annual average temperature and precipitation show the same trend from 1965 to 1982,antisymmetric change from 1983 to 1996,and the same trend from 1998 to 2012.Both summer precipitation and temperature basically showed antisymmetric changes with obvious trends.The trends of monthly runoff in the Dongjiang River are not significant,and those in the Xijiang River are more complicated.There is a significant jump in the Xijiang River,and the time point of the jump is October 2008.The first main cycle of Dongjiang,Xijiang and Beijiang runoff is 17,17 and 18 months,and there are 4-5 oscillations.The correlation between precipitation and runoff is stronger in January,March,April,June,and October for the Dongjiang River,and in May,October,and December for the Xijiang River.The correlations of temperature and precipitation are weaker.From the cross wavelet transform,we can get that there is a resonant cycle of positive correlation between runoff and precipitation in the highenergy region of Dongjiang,Xijiang and Beijiang rivers.In the low-energy region,there are two resonance cycles for Dongjiang and Beijiang,and one resonance cycle for Beijiang.The temperature and runoff of Dongjiang,Beijiang and Xijiang rivers have only one cycle in the high-energy region,and two resonance cycles in the low-energy region for Dongjiang and Xijiang rivers,and one resonance cycle for Beijiang river.The prediction levels of monthly runoff based on SARIMA model are B,B and A,which indicate that the prediction is good and can be used as operational forecasts.The prediction of monthly runoff based on NAR model,the prediction grade of NAR model for Dongjiang,Xijiang and Beijiang are all B-class,which indicates that the prediction effect is good and can be used for operational forecasting.the prediction of monthly runoff based on SARIMA-NAR combined model,the prediction scheme is A-class,so it can be used for operational forecasting,and the relative error of combined model is lower than that of single model.It shows that the prediction accuracy of the combined model based on the entropy weight method has been improved,and the prediction effect is better and more stable than that of two single models.