基于改进RVA法的黑河上游水文情势变化分析

客观地评价水文情势变化是进行河流生态修复和流域水资源综合管理的基础。改进RVA法将径流典型年份的变化纳入整体改变度的计算过程中,相对更全面地评价径流水文情势的变化。近几十年来黑河流域气候条件的发生显著变化,黑河上游河流水文情势的变化情况仍需进一步研究。以黑河上游为研究区域,应用M-K检验识别径流的突变年份,采用改进RVA法计算分析黑河上游河流水文情势变化。结果表明,黑河上游径流的突变年份为2002年,2002年前后分别以平水年和丰水年为主;采用RVA法计算的整体改变度为54.68%,而改进的RAV方法计算的整体改变度为74.62%,说明RVA法低估了黑河上游水文情势整体改变度;黑河上游径流水文情势变化主要包括:相比于1960—2002年,2003—2015年后各月平均流量均呈不同程度增加,但最小1日、3日、7日和最大7日流量减小,其余极端流量指标呈不同程度增加,高、低流量发生次数及历时变化微弱,流量平均增加率、减小率以及逆转次数均增加;采用改进的RVA法计算的黑河上游水文情势的整体改变度为74.62%,属于高度改变。气候变化是导致黑河上游水文情势高度改变的主要原因。

Flow regime alterations of upper Heihe River based on improved RVA

Objective evaluation of flow regime alteration is the foundation of river ecological restoration and integrated water resources management.Various approaches that take hydrological year types into consideration could objectively evaluate the altered flow regime.Due to climate change in the recent decades,the flow regime of upper Heihe River has altered and needs further research.Our study area was the upper Heihe River,where we employed an improved range of variability approaches to analyze the alterations of the flow regime.Firstly,we applied the Mann-Kendall method to identify the catastrophe point.We analyzed the flow regime using hydrological alteration indicator method.This method includes 33 parameters classified into five groups:The magnitude of monthly water conditions,magnitude and duration of annual extreme water conditions,timing of annual extreme water conditions,frequency and duration of high and low pulses,and rate and frequency of water condition changes.Based on these groups,we used the range variability approach to calculate the degree of alteration of these 33 parameters.We measured the difference in typical hydrologic years before and after the catastrophe point using the Euclidean distance.The degree of hydrologic alteration was calculated considering the alteration of these 33 parameters and the difference between typical hydrologic years.Our results indicated that the year 2002 was catastrophic point of the river flow regime.The main hydrological type years before and after 2002 were normal flow and wet years.The improved method calculated an alteration degree of 74.62%,while the range of variability approach showed an alteration of 54.68%,indicating underestimation of the effect.Compared to 1960-2002,the monthly mean streamflow in 2003-2015 increased to various extents in the upper Heihe River’s flow regime.The annual minima 1 day,3 day,7 day,and annual maxima 7 day decreased,whereas the other extreme water condition indicators increased.The frequency and duration of high and low pulses changed slightly,and the average peak flow duration decreased while the other indicators increased.Rate and frequency of water condition increased.The degree of hydrologic alteration was 74.62%considering the change of HYTs,which indicated a high alteration in the upper Heihe River’s flow regime.Climate change is the main reason causing the flow regime alteration.