Temporal And Spatial Evolution Of Runoff And Its Response To The Change Of Underlying Surface In Nenjiang River Basin

Hydrological system is a highly complex nonlinear system, Is the interaction,influence, circulation and transformation of various hydrological factors such as precipitation, evaporation. As the core part of the hydrological process, runoff plays a leading role in the system. In recent decades,due to the interaction of meteorological conditions and the underlying surface effect, the runoff of Nenjiang River Basin occurred significant change. But by the limit of watershed hydrological process observation data, it is different to describe the temple and spatial evolution of runoff process based on simple physical or mathematical methods. Therefore, it is important research topic to study the trend of runoff evolution and the response of runoff to the change of underlying surface in this filed.Precipitation is the main source of runoff, the spatial and temporal evolution of precipitation is the basic and important work to reveal the rules of runoff. Through an intuitive method, improved cumulative curve method, the Sen’s slope estimates and Mann-Kendall non parametric test analysis are used to analyze precipitation between the annual and the evolution.The result shows that the precipitation has no significant changes in the Nenjiang River Basin, but before the flood season(April) and after the flood season(October) monthly precipitation have obvious trend of change. Based on the spatial analysis function of Arc GIS, the spatial evolution law of the precipitation mass center is studied. The results show that the precipitation mass center is concentrated in the main flood season; the other months are relatively dispersed. And the annual precipitation has no significant change in the space. In summary, the precipitation of the Nenjiang River Basin both temporal and spatial is stable with no change. In order to facilitate the analysis, we can study the temporal and spatialevolution of runoff by ignoring the influence of precipitation to runoff.In this paper, combine with the five represent hydrological station of mainstream in Nenjiang River Basin, Eck optimized recursive digital filtering method segmentation runoff to surface runoff and underground runoff in benchmark period.Through analysis the evolution and distribution between river runoff, surface runoff and underground runoff of each catchment in a year and interannual, in upstream and downstream to further to reveal the differences between each catchment runoff water sources, composition and its causes. The river runoff is combined with surface runoff and underground runoff in upstream. In flood season, it is affected by both two kind of runoff; in dry season, it is only affected by the evolution of underground water. In spring, river runoff mainly combine with underground runoff, the evolution of the rules with the underground runoff are basically the same, especially in the dry season.In spring, river runoff is come from snowmelt runoff; in flood season, it is supplied by precipitation; in dry season, it is supplied by groundwater. The downstream river runoff is only supplied by groundwater in annual. From upstream to downstream, the runoff volume is smaller and smaller, the adulatory property of runoff is bigger and bigger. This is because the catchment area of downstream is bigger and bigger, runoff is affected by coupling factors of multiple effects in the process of flow concentration.On the one hand, under the effect of evaporation and infiltration, the runoff has a certain loss in the concentration process. On the other hand, the downstream is plain area, a lot of water are used to human activity.In the case of climate factors relatively stable, through analysis the relationship of precipitation and runoff can study hydrological effect variation law caused by the human activities change the underlying surface conditions. Then the change trends and change points of precipitation and runoff can be determined. This paper based on Intuitive method, Sen’s slope estimation method, Mann Kendall non parameter test,Spearman R‘ho non parametric test, Pettitt mutation test and improved cumulative curve method combined with Nenjiang River basin hydrological station during1955-2005 years(a total of 51 years), runoff sequence trend analysis and identifyingpoint mutations to describe the evolution of the runoff in Nenjiang River Basin. The results showed that the runoff has a significant downward trend and the abrupt change point occurred in 1979, the baseline period is from 1955 to 1979 years. Through a benchmark of accumulated precipitation and cumulative runoff data, a regression equation is established, simulation reference period rainfall runoff relationship.Accordingly, the quantitative calculating runoff based on responses to the change of the underlying surface. That 80’s runoff increased, the mid 90’s runoff is greatly reduced, which is mainly affected by the underlying surface changes caused by human activities.