Search

The variation of base flow is a comprehensive reflection of the change of regional climate and human activities,and it is an important element to maintain sustainable development of the ecosystem.In this study,the Kuye River catchment,a tributary of the Yellow River,with a drainage area of 8706 km2 on the Loess Plateau,was chosen to investigate the change trends and evolution characteristics of base flow.Based on Chapman-Maxwell base flow separation technique,the total runoff from Wenjiachuan hydrological station,which is the maximum control station in the Kuye River catchment,was separated into surface runoff and base flow.The nonparametric Mann-Kendall test and the Pettitt test were used to identify the trends and change points in the base flow during 1959 to 2005.The results indicated that:(1) In the past 50 years,a significant negative trend was detected in the annual base flow in all 7 time periods.For total year period,the average change rate is 0.628mm/a.The change points significantly occurred in 1980 and 1996.(2) Analysis of flow duration curves showed that,compared to the contrast period from 1959 to 1979,the relative changes of annual base flow for 5%,50% and 95% exceeding time were lowered by 30%,38% and 54%,respectively,in the treat period from 1980 to 1995,and the relative changes of annual base flow for 5%,50% and 95% exceeding time were lowered by 57%,68% and 100%,respectively in the coal mining period from 1996 to 2005.(3) The significant negative trend in base flow is a comprehensive effect of the change of regional climate and human activities,and the main factor is that excessive exploitation of a large area of coal resources and utilization of groundwater.

A new modified form of the rapid numerical difference recurrence formula was proposed to calculate the nonlinear Shrdinger equation,with ites of the pulse self-steepening and the intrapulse Raman scattering.Compared with the traditional analytical results of solitons and the solutions of Split-step Fourier method,the results show that the modified rapid numerical difference recurrence algorithm is a fast and precise numerical method,which takes into account simultaneously both the effects of the chromatic dispersion and the nonlinear Kerr effect together along each fiber segment,and the effects of all the higher-order nonlinear items of the optical medium.By using this method,it was validated successfully to simulate the supercontinuum generated as a result of the optical fiber nonlinear effects and the group velocity dispersion effects together.The formula was proved that it can provide some new ideas of research for the simulation of the other nonlinear phenomena in the optical medium.