Homogeneity analysis of streamflow records in arid and semi-arid regions of northwestern Iran

Homogeneity analysis of the streamflow time series is essential to hydrological modeling, water resources management and climate change studies. In this study, five absolute homogeneity tests and one clustering approach were used to determine the homogeneity status of the streamflow time series(over the period 1960–2010) in 14 hydrometric stations of three important basins(i.e., Aras River Basin, Urmia Lake Basin and Sefid-Roud Basin) in northwestern Iran. Results of the Buishand range test, von Neumann ratio test, cumulative deviation test, standard normal homogeneity test and Pettitt test for monthly streamflow time series detected that about 42.26%, 38.09%, 33.33%, 39.28% and 68.45% of the streamflow time series were inhomogeneous at the 0.01 significance level, respectively. Streamflow time series of the stations located in the eastern parts of the study area or within the Urmia Lake Basin were mostly homogeneous. In contrast, streamflow time series in the stations of the Aras River Basin and Sefied-Roud Basin showed inhomogeneity at annual scales. Based on the overall classification for the monthly and annual streamflow series, we determined that about 45.60%, 11.53% and 42.85% of the time series were categorized into the 'useful', 'doubtful' and 'suspect' classes according to the five absolute homogeneity tests. We also found the homogeneity patterns of the streamflow time series by using the clustering approach. The results suggested the effectiveness of the clustering approach for homogeneity analysis of the streamflow time series in addition to the absolute homogeneity tests. Moreover, results of the absolute homogeneity tests and clustering approach indicated obvious decreasing change points of the streamflow time series in the 1990 s over the three basins, which were mostly related to the hydrological droughts.     

皇甫川流域降水和人类活动对水沙变化的定量分析

采用线性趋势法、非参数Mann-Kendall趋势检验法、累积距平法及径流历时曲线法分析皇甫川流域1955-2010年水沙变化特征,通过水文分析法定量评价降水和人类活动对水沙变化的贡献率.结果表明:皇甫川流域径流量和输沙量均呈急剧减少趋势,尤其在20世纪80年代之后,减少更加显著,近10年(2000-2010)的平均径流量与输沙量相当于1950-1959年的约20％;皇甫站径流量和输沙量均在1979年发生突变;在变化期1980-2010年,人类活动对流域水沙变化的贡献占主导因素,约为70％,而降水所占比例为30％左右;自20世纪80年代始,大规模的水土保持措施(如退耕还林(草)、梯田建设、水库淤地坝等工程)等人类活动是流域水沙锐减的主要影响因素.     

嘉陵江流域降水及径流演变规律分析

流域降水与径流演变规律的异同性,可有效表征人类活动对流域径流的影响。基于嘉陵江流域1958—2008年水文、气象资料,探寻流域年降水量、年径流量的空间分布规律,采用经验正交函数和时间序列分析法,研究年降水量、降水量年内分配指数和年径流量的演变规律,对比演变规律的同步及异步变化特征。结果表明:年降水量自流域东南向西北递减,年径流深分别于涪江、渠江上游和流域北部、涪江中游、流域中游干流段出现相对高值和低值。流域年降水量、降水量年内分配未呈现显著变化趋势,无突变点,把口站北碚站年径流量下降趋势明显,于1990年产生突变;年降水量和年径流量主周期一致,均为35a和21a,但主周期显著程度不同;年降水量和年径流量于2002—2008年丰枯状态不同,径流相对于降水呈现强减少趋势。流域自然条件和水利水保措施、城市化等人类活动造成降水与径流主周期显著程度的差异,以及降水与径流趋势性、突变性及阶段性变化的不同步。     

气候因素对阿克苏河径流变化影响的定量评估

[目的]探究阿克苏河径流变化的归因.[方法]采用Mann-Kendall-Sneyers检验估计流域水文、气象数据的变化趋势和突变情况,并试图用3种改进的弹性系数法评估气候要素(尤其是温度)对阿克苏河径流变化的影响.[结果]径流和温度分别以11.73 m3/(s·10 a)和0.26℃/10 a的速率显著递增.降雨也呈...     

Sensitivity and vulnerability of water resources in the arid Shiyang River Basin of Northwest China

The sensitivity and vulnerability of water resources to climate change is difficult to assess. In this study, we used a conceptual hydrologic model to investigate the sensitivity of streamflow to climate change. We also proposed a framework to evaluate the vulnerability of water resources in arid regions. We applied this framework to a case study of the Shiyang River Basin in Northwest China. Results showed that the precipitation and streamflow in Shiyang River Basin exhibited no significant trends of change from 1956 to 2010. In the past five decades, however, the temperature increased significantly by 0.37°C per decade. According to the sensitivity assessment, a 10% increase in precipitation and a 1°C increase in temperature altered mean annual streamflow by averages of 14.6% and –0.5%, respectively, from 1988 to 2005. In the 2000s, the calculated vulnerability of water resources in Shiyang River Basin was more than 0.95, indicating severe vulnerability. The increase in the amount of precipitation and the implementation of water-saving measures can reduce the vulnerability of water resources in the future; if precipitation increases by 10% per decade and the use of irrigation water decreases by 15% in the 2030s, the evaluated value of water resources vulnerability will be reduced to 0.79. However, the region remains highly vulnerable. The proposed framework for vulnerability assessment can be applied to the arid regions in Northwest China, and the results of our efforts can identify adaptation strategies and improve the management of water resources in such regions.     

基于Copula函数的关中河流水文丰枯遭遇特征分析

引入Copula函数方法,对关中地区几条主要河流径流的丰枯遭遇特性及规律进行研究,分别选取渭河、泾河和黑河径流系列作为代表,对其两两间的丰枯遭遇状况进行了分析。结果表明：在丰枯同步频率中,两条河流间同平的频率大于同枯的频率和同丰的频率,同丰的频率最小;在各河流的丰枯异步频率中,两河流的丰平与平丰、丰枯与枯丰、平枯与枯平遭遇的概率基本一致;各河流间的丰枯遭遇概率、丰枯同步（共3种类型）频率略大于丰枯异步（共6种类型）频率。研究表明,Copula函数方法概念明确,适用性强,简便易用。     

渭河流域极端降雨变化趋势及其对水沙情势的影响

为探究渭河流域极端降雨变化趋势及其对水沙情势的影响,采用非参数趋势检验、突变检验和连续小波变换诊断了渭河流域1960—2019年的极端降雨指数及径流输沙序列的变异特征,通过双累积曲线法和相关分析法定量评估了流域极端降雨对水沙变化的影响。结果表明:各极端降雨指数呈阶段性波动变化,总体上PRCPTOT,RX5day和RX1day呈不显著下降趋势,R95pTOT,SDII和FSPTOT呈不显著上升趋势。各极端降雨指数均存在以4～6 a,11～12 a,28～29 a为周期的变化特征。径流与输沙量均呈显著减少趋势,分别在1993年、1999年发生突变,其中径流存在5 a和12 a的周期。各极端降雨指数均与径流、输沙量正相关,相比之下,输沙量与各极端降雨指数之间的相关系数偏低。极端降雨变化对径流与输沙量的减少具有重要影响。其中,PRCPTOT对径流减少的影响最大(29.65%),其次是RX5day(25.68%)和FSPTOT(25.95%)。PRCPTOT对输沙量减少的影响也是最大的(10.02%),其次是RX5day(7.12%)。综上,渭河流域水沙情势的变化受极端降雨的显著影响。     

基于SWAT模型的南渡江上游流域径流对气候变化的响应

为了评估未来气候变化对热带岛屿性森林流域径流的影响,以海南岛南渡江上游流域为例,构建本地化SWAT模型,基于CMIP6全球气候模式数据提取的气候变化信号,定量辨析了流域径流量对气候变化的响应。结果表明:(1)南渡江上游流域年平均径流量16.1 m³/s,旱季和雨季径流量分别占年径流量的17%,83%;(2)1961—2020年南渡江上游流域年平均径流减少趋势不显著,其中旱季径流增加4.6%,而雨季径流减少9.9%;(3)流域旱季径流增加量远低于雨季径流减少量致使年平均径流量减少,旱季径流增加由降水增多所致,雨季气温升高引起蒸发加剧是造成径流减少的关键;(4)在CMIP6计划的SSP119,SSP126,SSP434,SSP245,SSP460,SSP370和SSP585路径下,21世纪不同时期研究区径流变化主要受降水变化的影响,而21世纪后期气候变化加剧会引起研究区径流变化幅度加大。研究区径流对降水变化的敏感性高于气温,降水变化主导未来时期南渡江上游流域的径流量变化。     

Flow regime changes in three catchments with different landforms following ecological restoration in the Chinese Loess Plateau

The Chinese Loess Plateau is known as one of the most severe soil erosion regions in the world.Two ecological restoration projects,i.e.,the integrated soil conservation project since the 1970s and the'Grain for Green'project since 1999,have been progressively implemented to control the soil erosion in this area.Ecological restoration has greatly changed flow regime over the past five decades.However,the mechanism of how flow regime responds to ecological restoration among landforms remains poorly understood.In this study,we investigated the temporal dynamics of flow regime in three catchments,i.e.,Wuqi,Honghe and Huangling hydrological stations,respectively representing the loess hilly-gully,loess table-gully and rocky mountain(covered by secondary forest)areas in the Chinese Loess Plateau,using daily hydrological data during the 1960s–2010s.The nonparametric Mann-Kendall test,Pettitt's test and daily flow series were used to investigate the changes of flow regime.Significantly negative trends of annual streamflow were detected at the Wuqi and Honghe stations,except for the Huangling station.The annual baseflow at the Wuqi station showed a significantly positive trend whereas a significantly negative trend was observed at the Honghe station,and there was no significant trend at the Huangling station.It was interesting that baseflow index significantly increased during the whole period in all catchments.However,the trends and change points of daily flow series derived by different percentages of exceedance and extreme series in different consecutive days varied among individuals.Based on the change points analysis of annual streamflow,we divided data series into three periods,i.e.,the baseline period(from 1959 and 1963 to 1979,PI),the integrated soil conservation period(1980–1999,PII)and the'Grain for Green'period(2000–2011,PIII).We found that streamflow decreased due to the reduction of high streamflow(exceeding 5%of time within a year)and median streamflow(50%)in PII and PIII at the Wuqi and Honghe stations.However,low flow(95%)increased in PII and PIII at the Wuqi station while decreased at the Honghe station.Streamflow change at the Huangling station was more stable,thus potentially resulting in much less soil erosion in the forestry area than in the other areas.The great improvement in ecological environment on the Chinese Loess Plateau revealed the advantages of ecological restoration in reducing flood amount and compensating streamflow at a regional scale.     

Microgeographical variation in ovum size of the blacktail shiner, Cyprinella venusta Girard, in relation to streamflow

Abstract – There is a strong, positive correlation between egg size and the discharge variable mean annual runoff among populations of Cyprinella venusta Girard from streams in different drainages ranging across the Gulf Coastal Plain of the southern United States. This variation may have resulted from selection for larger egg size, hence larger offspring size, because of greater environmental fluctuation or a greater number of floods in streams with higher runoff. In the present study, we examined C. venusta from populations inhabiting streams varying in mean annual runoff within a single drainage and found a similar correlation between ovum size and runoff. Therefore, the egg size–runoff relationship exists at a much smaller (i.e., intra-drainage) spatial scale than previous research (based on widespread inter-drainage variation) has shown. We also attempted to establish a link between mean annual runoff and streamflow-mediated disturbance as indicated by predictability of streamflow, monthly coefficients of variation in discharge and number of days with extreme low and high flows. Although the overall predictability of discharge did not differ among streams, the streams with high mean annual runoff were characterized by smaller coefficients of variation in winter, fewer days of extremely low flows and a trend toward higher flows in late summer and early fall. At the intra-drainage scale, higher coefficients of variation did not accurately reflect the numbers of extreme flows. These results call into question the use of coefficients of variation in discharge as indicators of disturbance. Given that eggs, larvae and small juveniles of C. venusta are present in late summer and early fall, when flows in high runoff streams tend to be high relative to low runoff streams, we conclude that these high flows may act as a selective force causing the evolution of larger egg size.