Hydrological Regimes Change And Response Analysis Of Taojiang River Basin In The Upper Reaches Of Ganjiang River

The fluctuation of river hydrological situation drives the development of energy process,material cycle,interaction between organisms and habitat status of rivers and river basins ecosystems.As for the channel of Zhejiang-Jiangxi-Guangdong Canal planned in the Outline of Inland River Shipping Development issued by the Ministry of Transport of the State Council,it is bound to cause great disturbance to the ecological and hydrological situation of Taojiang River Basin.Taking the Taojiang River Basin as the study area,based on the measured runoff data of Julongtan Hydrological Station,the overall hydrological situation change in the basin is quantitatively analyzed by IHA/RVA method,and based on the precipitation data of 27 stations,the Tyson polygon method is used to convert the average precipitation into 8 precipitation indexes,and the present situation of precipitation in the basin is analyzed.Based on the land cover data of 1987,1997,2007 and 2017,the land cover transfer matrix,dynamic change of land cover type,patch type index and landscape level index were used to analyze the spatiotemporal change characteristics of land cover in the basin in recent 40 years.Then the correlation analysis method is used to analyze the influence of natural precipitation and land cover on the hydrological regime of the basin.The results show that:(1)with the decrease of rainfall in the basin,the average annual discharge shows a downward trend,and the maximum mutation point of discharge series is 2004 according to cumulative anomaly,moving average test and Mmurk K trend test.On the other hand,the average monthly flow changes obviously,the flood season is 3 months ahead of schedule,and the minimum flow at the beginning of the year slows down;most of the extreme flow tends to decrease before and after the change;the annual 1-day minimum flow increases,the occurrence time is in advance,and the range of change is expanded.on the contrary,the average number of pulses of high flow is 8,that of low flow is 10,the duration of high flow increases by 3.95%,and the duration of low flow decreases by 73.6%.After the sudden change,the number of traffic fluctuations increased,the number of reversals increased by 78.52%,and the rising rate of Flow reduction and the falling rate increased.Most of the 32 hydrological indicators in Taojiang belong to low degree change of 62.5%,followed by medium degree of 9.2%,high degree of8.3%,indicating that the basin is in a good trend of change.(2)Light rain is the main form of precipitation in the basin,accounting for about 40%of the annual precipitation.Before 2000’s,the basin showed the stage of precipitation days and precipitation decreasing and precipitation intensity increasing,and then changed to the state of precipitation days and precipitation increasing and precipitation intensity decreasing.The present situation of the downward trend of precipitation in the basin is more in the north than in the south,and a gradual decreasing trend in the east and west of the middle and north.The daily maximum rainfall and extreme rainfall index are high in the southeast and low in the northwest,while the extra heavy rainfall forms a "high-low" transition trend from east to west.Extreme rainfall shows a rapid decline in the north-central and northwest and a slow rise in the south and east.The average daily precipitation in most areas of the basin showed a slow upward trend,and the overall increase was low in the north and middle of the basin,especially in most of Quannan County and the southwest of Longnan County.(3)In the past 40 years,with the advance of urbanization,the area of grassland,water and unused land has always shown an increasing trend,forest land first increased and then decreased,the area of cultivated land always decreased,and the area of construction land increased significantly,indicating that human activities gradually concentrated and spread outward along the center of the city.The watershed landscape pattern jumps greatly from 1997 to 2007,but the connectivity and aggregation degree between different landscape types tend to be stable after 2007.In 2017,the landscape pattern of the watershed had the best aroma uniformity and diversity,that is,the distribution diversity of landscape types was relatively high,which increased significantly after 1997 and lasted for 20 years.(4)Rainfall intensity is the main factor that affects the change of hydrological situation,and there are more than 10 hydrological situation indicators that have passed the significance test,among which the days of heavy rain and the days of heavy rain are particularly significant in response to high-flow pulse and high-flow duration.According to the response relationship,it shows that the cultivated land area reduction and the number of low-flow pulses increases,the minimum flow gradually increases in 90 days per year,and the reversal index of water flow decreases.The decrease of forest land area has significant influence on the gradual decrease of the minimum annual discharge of 1d,30 d,90d and the rate of discharge decline.The decrease of unused land and the increase of the maximum flow in 30 days per year,the delay of the occurrence of the maximum flow,and the increase rate of the minimum flow and the flow in30 days are also echoed.Although the water area is affected by the fluctuation of rainfall in the previous period,the area change is not significant because of its small proportion.With the rapid development of urbanization,the duration of high flow rate is slowly prolonged,and the occurrence time of minimum flow rate is rapidly delayed.Urbanization also prolongs the flood season,when the dry season is delayed,the discharge becomes smaller.,thus gradually increasing the degree of hydrological change in the basin,but it is still in a good trend.