Changes Of Precipitation Characteristics In The Pearl River Delta Urban Agglomeration

Precipitation is the most important link in the water cycle,affected by climate change and human activities.The characteristics of global and regional precipitation have changed significantly.The uneven distribution of precipitation in time and space is the direct cause of the frequent occurrence of droughts and floods in my country.Therefore,studying the characteristics of regional precipitation changes will help to understand the law of regional water cycle changes.It can also provide important support for regional water resources planning and management,regional flood prevention and disaster mitigation as well as emergency management.It has important scientific significance and practical value.The Pearl River Delta Urban Agglomeration is one of the three most promising urban agglomerations in my country,and it is also one of the areas with the most active economic development and the fastest urbanization development in China.The daily precipitation data of 58 meteorological stations from1961 to 2017 are used to analyze the temporal and spatial characteristics of precipitation in the Pearl River Delta Urban Agglomeration in order to explore the impact and contribution of urbanization to regional precipitation changes and identify the correlation between climatic conditions and regional precipitation changes in this paper.In this way,the evolution of precipitation in the Pearl River Delta Urban Agglomeration is explained,which provides a reference for scientific response to regional water resources utilization,disaster prevention and mitigation under the changing environment.(1)Temporal and spatial variation characteristics of regional precipitationDaily precipitation records from 58 meteorological stations in the Pearl River Delta Urban Agglomeration during 1961-2017 are used to discuss the inter-annual variation trend of annual precipitation,different grade precipitation and floods season Precipitation.Mann-Kendall mutation method and sliding T test are selected to identify the abrupt changes of precipitation.Morlet wavelet analysis is applied to determine the precipitation cycle.EOF analysis and Kriging interpolation method are exploited to evaluate the spatial distribution of precipitation.The results show that the average annual precipitation of the Pearl River Delta urban agglomeration in 57 years has increased at a rate of 21.13mm/10 a,and the precipitation was unevenly distributed throughout the year,mainly in the flood season(April to September).Further research has found that the change trend of the precipitation characteristic value during the flood season and before and after the flood season are the same.Precipitation amount and precipitation intensity both show an increasing trend.The number of precipitation days shows a decreasing trend and the precipitation characteristic value in the first flood season is slightly higher than that in the later flood season.Seasonal precipitation in summer(43%)>spring(33%)>autumn(15.5%)>winter(8.5%),except for the decrease in autumn precipitation,the precipitation in each season has increased to varying degrees,but the trend of change is not significant,Summer precipitation increases the fastest,with a growth rate of 14mm/10 a.The precipitation events are dominated by light-rain events,while the precipitation amount is mainly contributed by heavy rain and torrential rain(>60%).The precipitation of moderate rain and above has increased to varying degrees.The increasing trends of heavy rain and torrential rain are both greater than 10mm/10 a.(2)The impact of urbanization on regional precipitationBased on land use data,DMSP lighting data and population density data,meteorological stations in the study area are empirically divided into three types to evaluate the impact of urbanization on the temporal and spatial distribution of precipitation,the difference in precipitation between urban and rural areas and the contribution rate of urbanization.The results show that urbanization may have the opposite effect on precipitation: urbanization has a certain degree of restraint on light rain,but it has a certain degree of enhancement on moderate rain,heavy rain and torrential rain.Urbanization makes the positive difference in precipitation between urban and rural areas larger and larger,while the negative difference decreases.However,the differences in precipitation between urbanization stations and rural stations are obviously smaller than that between urban stations and rural stations,indicating that the impact of urbanization on the difference in precipitation between urban and rural areas may be limited.In addition,the level of urbanization may affect the contribution rate of urbanization to precipitation changes,and precipitation changes in the later stages of urbanization are affected by more other factors.(3)The impact of climatic conditions on regional precipitationBased on meteorological elements and atmospheric circulation,the correlations between climatic conditions and precipitation in the Pearl River Delta Urban Agglomeration are analyzed by the methods of pearson correlation analysis,cross wavelet and coherent wavelet methods.The results show that relative humidity has the most significant impact on precipitation,while temperature,wind speed and air pressure have relatively small impacts on precipitation,with slight differences between seasons.The sites with strong correlations are mainly located in the Pearl River Estuary and northern mountainous areas.ENSO and IOD have a significant impact on annual precipitation and the effects of circulation indices on seasonal precipitation are different:ENSO and IOD have a greater impact on spring and winter precipitation and summer precipitation is most affected by PDO.Besides,NAO and IOD have a significant impact on autumn precipitation.From the Pearson diagram,the influence of NAO and PDO indexes on annual precipitation is more obvious,especially for the previous year's NAO and the current year's PDO.The spring and winter precipitation are more affected by ENSO,NAO,IOD and PDO than the summer and autumn precipitation.Precipitation in spring,summer and winter is affected by PDO,IOD and ENSO respectively,while precipitation in autumn is mainly affected by NAO and IOD.