Study On Precipitation Distribution Characteristics Of Longchuan River Basin In Dry-hot Valley In Hengduan Mountains

Water resources are of great significance to human production and life.Precipitation is the direct source of terrestrial water resources and the first link of water cycle.In recent years,the extreme of precipitation has gradually increased under the influence of global warming.The increase of extreme precipitation had a great and far-reaching impact on economic development,food production,ecological environment and life safety.At present,the study on extreme precipitation and its trend has become a research hotspot in the field of meteorology and hydrology in China.In this paper,the Longchuan River Basin in Dry-hot Valley in Hengduan Mountainous,where the contradiction between water and heat is prominent,was studied.The daily precipitation data from 1978 to 2015 of 26 rainfall stations in the valley were selected.The spatial and temporal distribution and variation characteristics of precipitation and extreme precipitation and vertical differentiation characteristics of precipitation are analyzed by means of trend analysis,periodic analysis and spatial interpolation.It provides theoretical basis and reference for ecological protection,ecological restoration,efficient allocation and utilization of water resources,disaster prevention and mitigation,and protection of water conservancy projects.The results are as follows:(1)The annual average precipitation and the number of rainy days in Longchuan River Basin showed a downward trend in interannual variation,and the decreasing trend of rainy days was obvious(P < 0.05),but the daily precipitation intensity showed an increasing trend(P < 0.1).Extreme precipitation showed an increasing trend on the whole.Extreme precipitation days decreased slightly,persistent precipitation days decreased,and persistent drought days increased.The annual distribution of precipitation in the basin is mainly concentrated in JuneSeptember(flood season).The precipitation in flood season accounts for 73.2% of the annual precipitation,which is significantly correlated with the annual average precipitation at the level of 0.01.The probability of extreme precipitation in July is the highest,24.9%,and the contribution rate is the highest,25%.(2)The precipitation in spring and winter of Longchuan River Basin showed an upward trend,with the annual trend rates of 4.8 mm/10 a and 1.5 mm/10 a,respectively;the precipitation in summer and autumn showed a downward trend,with the annual trend rates of-5.9 mm/10 a and-15.6 mm/10 a,respectively.The change trend in autumn passed the 0.1 significance test.Except autumn,rainy years in spring,summer and winter are lower than those in rainy years.(3)Morlet wavelet analysis shows that there are five main oscillation periods in the annual average precipitation of Longchuan River basin,which are 28 a,22a,13 a,6a and 2a respectively.The oscillation period of about 28 a is the strongest,and it is the first main period of annual average precipitation.There are 27 a,22a,6a and 4a main oscillation periods in the extreme precipitation,and the first main period is 22 a time scale with the most obvious oscillation.(4)The annual precipitation,extreme precipitation and consecutive wet days in Longchuan River Basin show a decreasing trend from southwest mountainous area to northeast dry-hot valley area,while the trend of consecutive dry days is opposite.The lower slopes from the high mountainous to the dry-hot valley is the high value area of extreme precipitation threshold and daily precipitation intensity.It is also the low value area of extreme precipitation days and rainy days.This indicates that extreme precipitation events are more likely to occur in this area,and the extreme precipitation threshold and daily precipitation intensity increase with the decrease of altitude from the southwestern mountainous area to this area.The extreme precipitation days and rainy days are opposite.(5)The annual precipitation in Longchuan River Basin will increase by 23 mm for every 100 m elevation rise.The annual average precipitation,the total amount of extreme precipitation and the days of persistent precipitation are positively correlated with altitude(P<0.01),and the days of rain and extreme precipitation are positively correlated with altitude(P<0.05),while the days of persistent drought are negatively correlated with altitude rise(P<0.01).