Analysis of changes in the relationship between precipitation and streamflow in the Yiluo River, China

The Yiluo River is the largest tributary of the middle and lower Yellow River below the Sanmenxia Dam. Hydro-climatic variables have changed in the Yiluo River during the last half century. In this study, the trends in the annual precipitation and streamflow were analyzed in the Yiluo River during 1960–2006. The results indicated that both the annual precipitation and streamflow decreased significantly (P?<?0.05) from 1960 to 2006. Pettitt’s test shows that there was a change point for annual streamflow series around the year 1986 (P?<?0.05), while there was no change point identified for the annual precipitation series from 1960 to 2006. Annual streamflow decreased more significantly than annual precipitation since 1986. The relationship between the annual precipitation and streamflow presented a non-stationary state since 1986. This non-stationary relationship was mainly influenced by human activities. The average annual amount of water diversion from the Yiluo River increased significantly since the mid-1980s, accounting for 31.3 % of the total streamflow decrease from 1986 to 2006. In addition, land use/cover change (LUCC) contributed to 27.1–29.8 % of the decrease in streamflow. Human activities, including water diversion and LUCC, together contributed to 58.4–61.1 % of the decrease in streamflow and led to the non-stationary relationship between the annual precipitation and streamflow from 1986 to 2006. This study detected the changes in the precipitation–streamflow relationship and investigated the possible causes in the Yiluo River, which will be helpful for the understanding of the changes in streamflow in the Yellow River Basin.     

澜沧江-湄公河流域径流与气候因子变化的季节差异特征研究

根据DELWARE温度和降水数据、GLDAS蒸散发数据和湄公河干流9个水文站的实测径流,采用回归分析、均值T检验和低通滤波,分析了该流域气候和径流在1950-2017年间的变化情况,经分析表明流域内气候和径流在研究时段内有较大变化,而且在不同的月份呈现不同的变化特征。流域年平均温度整体呈增加趋势,2008年后的平均温度相对2008年前平均温度有显著增加;流域年平均降水的变化幅度不大;流域平均蒸散发在12月-次年2月呈下降趋势,其他月份呈增加趋势,2008-2017年月平均蒸散发与1950-2007年月平均蒸散发相比大幅提升,尤其是在6-10月;湄公河流域年径流没有显著变化,但径流在12月-次年4月呈上升趋势,7-10月呈下降趋势,其中,上升趋势比下降趋势显著,1-4月径流上升趋势在2008年之后更为显著;最小径流在2008年后有显著增加趋势,最大径流在2008年后呈下降趋势;年流量逆转次数自20世纪90年代起有明显升高趋势。通过比较温度、降水、蒸散发和径流在不同时间段的变化情况,可以看出径流在2008年后变化趋势和气候自然变化关系不显著,但可能跟大坝蓄水能力显著提高等人为活动有较大关系。     

45年来塔里木河流域气候变化对径流量的影响研究

根据塔里木河流域40个气象站1961-2005年的降水、 气温资料及源区内7个水文站1957-2005年年径流量资料, 利用Mann-Kendall检验, 分析了近45年来塔里木河流域的气候变化的特征, 探讨了气候变化对塔里木河流域水资源的影响。结果表明： 整个流域除个别站点外, 塔里木河流域气温整体呈显著上升趋势, 且以秋季最显著, 降水增加以夏季最明显。特别是中天山南坡, 而流域西南部、 和田地区和巴州南部的降水量几乎没有增加。根据Mann-Kendall检验结果, 除阿克苏河年径流量呈显著增加趋势外, 其它3条源流（和田河、 叶尔羌河、 开都河）径流量近45年变化趋势均不显著。     

基于陆面水文耦合模式CLHMS的淮河流域水文过程的模拟评估及其不确定性分析

利用最新的CFSR(Climate Forecast System Reanalysis)再分析及观测的降水和地表气温资料驱动陆面水文耦合模式CLHMS(Coupled Land surface and Hydrologic Model System),对淮河流域1980~2003年共24年的水文水循环过程进行了模拟,系统评估了CLHMS对淮河流域水文过程的模拟能力及其不确定性。分析结果表明,CLHMS模式对淮河流域水文过程具有良好的模拟能力,模式尤其对湿润年份流域的水量平衡以及河道流量的季节、年际变化具有很强的模拟能力,而对降水偏少的干旱年份,模式模拟的河道流量通常会高于观测实况,与实况间存在着一定的偏差,而这也是导致CLHMS对流域水文过程模拟能力存在显著年代际差异的主要原因。基于三组不同降水强迫的流域水文过程模拟结果比较表明,降水驱动资料准确与否是陆面水文模拟最主要的不确定性来源之一,正是由于CFSR再分析降水与观测降水之间存在较大的差异,从而导致CFSR降水驱动下模式模拟的淮河流域河道流量与观测存在较大的偏差,其模拟性能相对较差。进一步分析还表明,可以保持较强降水日变化的时间解集方法,也是保证合理模拟流域水文过程的重要因素。     

Validating the Runoff from the PRECIS Model Using a Large-Scale Routing Model

The streamflow over the Yellow River basin is simulated using the PRECIS （Providing REgional Climates for Impacts Studies） regional climate model driven by 15-year （1979-1993） ECMWF reanalysis data as the initial and lateral boundary conditions and an off-line large-scale routing model （LRM）. The LRM uses physical catchment and river channel information and allows streamflow to be predicted for large continental rivers with a 1°×1° spatial resolution. The results show that the PRECIS model can reproduce the general southeast to northwest gradient distribution of the precipitation over the Yellow River basin, The PRECIS- LRM model combination has the capability to simulate the seasonal and annual streamflow over the Yellow River basin. The simulated streamflow is generally coincident with the naturalized streamflow both in timing and in magnitude.     

哈萨克斯坦北部伊希姆河径流对气候变化和人类活动的响应

基于1933—2016年哈萨克斯坦北部伊希姆河彼得罗巴甫洛斯克水文站流量观测数据以及流域内格点气象数据,利用线性趋势法、Mann-Kendall检验、相关普查法和累积量斜率变化率比较法等方法,探讨了气候变化背景下伊希姆河流量变化及其主要驱动因子。结果显示：(1)伊希姆河流域近84年气温和降水呈上升趋势,且在20世纪70年代后增加趋势更加明显。(2)伊希姆河流量年内分布不均,年际流量变化总体呈下降趋势,但趋势不明显。(3)伊希姆河流量受流域内降水和气温共同影响,其中降水与流量相关性最大,且降水的变化对流量补给具有滞后性,6—9月气温对同时期流量影响较大。(4)T₁时段(1969—1996年)和T₂时段(1997—2016年)与T时段(1933—1968年)相比,气候变化对流量减少的贡献率分别为16.09%和44.83%,而人类活动对流量减少的贡献率为83.91%和55.17%。流域内水资源的开发及利用、人口数量和土地利用方式的变化等人类活动因素在很大程度上影响了伊希姆河流量。     

Impacts of climate variability and human activities on decrease in streamflow in the Qinhe River,China

Under the impacts of climate variability and human activities, there are statistically significant decreasing trends for streamflow in the Yellow River basin, China. Therefore, it is crucial to separate the impacts of climate variability and human activities on streamflow decrease for better water resources planning and management. In this study, the Qinhe River basin (QRB), a typical sub-basin in the middle reach of the Yellow River, was chosen as the study area to assess the impacts of climate variability and human activities on streamflow decrease. The trend and breakpoint of observed annual streamflow from 1956 to 2010 were identified by the nonparametric Mann–Kendall test. The results showed that the observed annual streamflow decreased significantly (P?<?0.05) and a breakpoint around 1973 was detected. Therefore, the time series was divided into two periods: “natural period” (before the breakpoint) and “impacted period” (after the breakpoint). The observed annual streamflow decreased by 68.1 mm from 102.3 to 34.2 mm in the two periods. The climate elasticity method and hydrological model were employed to separate the impacts of climate variability and human activities on streamflow decrease. The results indicated that climate variability was responsible for 54.1 % of the streamflow decrease estimated by the climate elasticity method and 59.3 % estimated by the hydrological modeling method. Therefore, the climate variability was the main driving factor for streamflow decrease in the QRB. Among these driving factors of natural and anthropogenic, decrease in precipitation and increase in water diversion were the two major contributions of streamflow reduction. The finding in this study can serve as a reference for regional water resources management and planning.     

博斯腾湖流域气候变化及其对径流的影响

利用博斯腾湖流域开都河、黄水沟和清水河的出山口水文站月径流量和气象站月平均数据，开展变化特征分析和径流变化对气候因子的响应研究。结果表明，博斯腾湖流域年际气候变化以气温上升为主，降水量增加趋势不显著；域内主要河流径流量持续上升。突变检验发现，三条入湖河流90年代之前径流量增加主要是域内降水量增加的结果，随后受气温上升导致冰雪消融加快也对径流量的增加有贡献。相关分析结果显示，博斯腾湖三条入湖河流年径流量变化主要受4月和7月降水因子影响。此外，开都河的径流变化还表现出对8月气温和降水的显著响应，同时开都河流域集水区冰川的面积和占比均大于黄水沟和清水河流域，这表明冰川融水补给对开都河径流的影响大于黄水沟和清水河。所建立的气候因子-径流量多元线性回归模型，能够很好的模拟开都河、黄水沟和清水河的径流变化过程，证明了博斯腾湖流域水文变化受气候因子的显著影响。     

Streamflow trend analysis by considering autocorrelation structure,long-term persistence,and Hurst coefficient in a semi-arid region of Iran

Due to the substantial decrease of water resources as well as the increase in demand and climate change phenomenon, analyzing the trend of hydrological parameters is of paramount importance. In the present study, investigations were carried out to identify the trends in streamflow at 20 hydrometric stations and 11 rainfall gauging stations located in Karkheh River Basin (KRB), Iran, in monthly, seasonal, and annual time scales during the last 38 years from 1974 to 2011. This study has been conducted using two versions of Mann–Kendall tests, including (i) Mann–Kendall test by considering all the significant autocorrelation structure (MK3) and (ii) Mann–Kendall test by considering LTP and Hurst coefficient (MK4). The results indicate that the KRB streamflow trend (using both test versions) has decreased in all three time scales. There is a significant decreasing trend in 78 and 73 % of the monthly cases using the MK3 and MK4 tests, respectively, while these percentages changed to 80 and 70 % on seasonal and annual time scales, respectively. Investigation of the trend line slope using Theil–Sen’s estimator showed a negative trend in all three time scales. The use of MK4 test instead of the MK3 test has caused a decrease in the significance level of Mann–Kendall Z-statistic values. The results of the precipitation trends indicate both increasing and decreasing trends. Also, the correlation between the area average streamflow and precipitation shows a strong correlation in annual time scale in the KRB.     

Changes in Fire and Climate in the Eastern Iberian Peninsula (Mediterranean Basin)

Fire is a dominant ecological factor in Mediterranean ecosystems, and changes in the fire regime can have important consequences for the stability of our landscapes. In this framework I asked firstly, what is the trend in fire number and area burned in the eastern Iberian Peninsula, and then, to what extent is the inter-annual variability of fires determined by climatic factors. To answer these questions I analysed the meteorological data (temperature and precipitation) from 350 stations covering the eastern Iberian Peninsula (1950–2000), and the fire records for the same area (historical data, 1874–1968, and data from recent decades, 1968–2000). The results suggested a slight tendency towards decreasing summer rainfall and a clear pattern of increasing annual and summer temperatures (on average, annual temperatures increased 0.35 °C per decade from 1950 to 2000). The analysis of fire records suggested a clear increase in the annual number of fires and area burned during the last century; however, in the last three decades the number of fires also increased but the area burned did not show a clear trend. For this period the inter-annual variability in area burned was significantly related to the summer rainfall, that is, in wet summers the area burned was lower that in dry summers. Furthermore, summer rainfall was significantly cross-correlated with summer area burned for a time-lag of 2 years, suggesting that high rainfall may increase fuel loads that burn 2 years later.     

Atmospheric moisture budget and floods in the Yangtze River basin, China

In this paper, we explored the trends of the atmospheric moisture budget, precipitation, and streamflow in summer during 1961 to 2005 and possible correlations between them by using the linear regression method in the Yangtze River basin, China. The results indicate that: (1) increasing tendencies can be detected in the atmospheric moisture budget, precipitation and streamflow in the Yangtze River basin; however, the significant increasing trends occur only in the atmospheric moisture budget and precipitation in the middle and lower Yangtze River basin; (2) both the ratio of summer moisture budget to annual moisture budget and the ratio of summer precipitation to annual precipitation exhibit a significant increasing trend in the Yangtze River basin. The ratio of summer streamflow to annual streamflow is in a significant increasing trend in Hankou station. Significant increasing summer precipitation can be taken as the major controlling factor responsible for the higher probability of flood hazard occurrences in the Yangtze River basin. The consecutively increasing summer precipitation is largely due to the consistently increasing moisture budget; (3) the zonal geopotential height anomaly between 1991 and 2005 and 1961 and 1990 is higher from the south to the north, which to a large degree, limits the northward propagation of the summer monsoon to north China. As a result, the summer moisture budget increases in the middle and lower Yangtze River basin, which leads to more summer precipitation. This paper sheds light on the changing properties of precipitation and streamflow and possible underlying causes, which will be greatly helpful for better understanding of the changes of precipitation and streamflow in the Yangtze River basin.     

陆面—水文耦合模式的参数率定及改进研究

基于淮河流域的地形、岩石地质类型等空间分布特征,对陆面—水文耦合模式CLHMS1.0(Coupled Land Surface-Hydrological Model version 1.0)的河道曼宁糙率系数、水力传导度两个关键参数进行了率定;在此基础上,通过基于CLHMS1.0的多组敏感性试验,分析了河道曼宁糙率系数、水力传导度对CLHMS1.0模拟淮河流域水文过程的影响。研究结果表明,淮河流域上游王家坝子流域曼宁糙率系数的减小,可以显著提高模式对王家坝水文控制站上游模拟的水流流速,减小了模式对王家坝洪峰来临时间模拟偏迟的误差;依据淮河不同子流域的岩石地质类型选定更为合理的水力传导度参数后,模式对淮河流域河道流量等水文过程的模拟更为准确。利用参数率定后的CLHMS1.0对淮河流域1980~1987年逐日水文过程进行了模拟,与观测实况比较结果表明,采用了新的河道曼宁糙率系数和水力传导度参数后,模式对淮河流域逐日水文过程的模拟能力显著提高,且可以更合理地模拟出地表产流和地下水补给对流域河道流量的相对贡献。     

2010—2100年淮河径流量变化情景预估

根据淮河流域14个气象站点1964—2007年观测降水量与温度数据和ECHAM5/MPI-OM模式在3种排放情景下对该流域2001—2100年的气候预估,利用人工神经网络模型预估淮河蚌埠站2010—2100年逐月径流量变化。计算结果表明:3种排放情景下2010—2100年淮河径流量年际变化幅度差异较大,SRES-A2情景总体处于波动上升趋势,其中2051—2085年上升趋势显著;SRES-A1B情景2024—2037年年平均流量显著降低;SRES-B1情景年平均流量的变率甚小。季节分析表明:春季径流量在2010—2100年变幅最小,距平百分率在-15.1%～18.6%之间小幅波动。夏季平均流量在2040年代前呈下降趋势,之后小幅波动上升。秋、冬季平均流量SRES-A2和SRES-A1B情景变幅显著,其中,秋季SRES-A2情景2060年代距平百分率下降达50.6%,为3种情景下各季节径流量降幅之最;冬季SRES-A1B情景2050年代其增幅达到54.7%,亦为上升幅度之最。     

土地利用变化对长江流域气候及水文过程影响的敏感性研究

使用区域气候模式(RegCM3)和大尺度汇流模型(LRM), 研究土地利用/植被覆盖变化对长江流域气候及水文过程的影响。RegCM3嵌套于欧洲数值预报中心 (ECMWF) 再分析资料ERA40, 分别进行了中国区域在实际植被和理想植被分布情况下两个各15年 (1987～2001年) 时间长度的积分试验。随后, RegCM3 两个试验的输出径流结果分别用来驱动LRM, 研究土地利用/植被覆盖变化对长江流域河川径流的影响。研究结果指出, 中国当代土地利用变化对长江流域降水、蒸散发、径流深及河川径流等水文气候要素的改变较大, 对气温的改变并不明显。土地利用变化引起长江干流河川径流量在夏季(6～8月)有所增加, 并且越向下游增加幅度越大, 其中大通站径流量增加接近15%。总体而言, 土地利用改变加剧了长江流域夏季水循环过程, 使得夏季长江中下游地区降水增多, 径流增大。     

Effects of climate change on annual streamflow using climate elasticity in Poyang Lake Basin, China

Hydrological processes depend directly on climate conditions [e.g., precipitation, potential evapotranspiration (PE)] based on the water balance. This paper examines streamflow datasets at four hydrological stations and meteorological observations at 79 weather stations to reveal the streamflow changes and underlying drivers in four typical watersheds (Meigang, Saitang, Gaosha, and Xiashan) within Poyang Lake Basin from 1961 to 2000. Most of the less than 90th percentile of daily streamflow in each watershed increases significantly at different rates. As an important indicator of the seasonal changes in the streamflow, CT (the timing of the mass center of the streamflow) in each watershed shows a negligible change. The annual streamflow in each watershed increases at different rates, with a statistically significant trend (at the 5 % level) of 9.87 and 7.72 mm year^?1, respectively, in Meigang and Gaosha watersheds. Given the existence of interactions between precipitation and PE, the original climate elasticity of streamflow can not reflect the relationship of streamflow with precipitation and PE effectively. We modify this method and find the modified climate elasticity to be more accurate and reasonable using the correlation analysis. The analyses from the modified climate elasticity in the four watersheds show that a 10 % increase (decrease) in precipitation will increase (decrease) the annual streamflow by 14.1–16.3 %, while a 10 % increase (decrease) in PE will decrease (increase) the annual streamflow by ?10.2 to ?2.1 %. In addition, the modified climate elasticity is applied to estimate the contribution of annual precipitation and PE to the increasing annual streamflow in each watershed over the past 40 years. Our result suggests that the percentage attribution of the increasing precipitation is more than 59 % and the decreasing in PE is less than 41 %, indicating that the increasing precipitation is the major driving factor for the annual streamflow increase for each watershed.     

The Linkage between Two Types of El Ni?o Events and Summer Streamflow over the Yellow and Yangtze River Basins

It is generally agreed that El Nino can be classified into East Pacific(EP)and Central Pacific(CP)types.Nevertheless,little is known about the relationship between these two types of El Ni?o and land surface climate elements.This study investigates the linkage between EP/CP El Ni?o and summer streamflow over the Yellow and Yangtze River basins and their possible mechanisms.Over the Yellow River basin,the anomalous streamflow always manifests as positive(negative)in EP(CP)years,with a correlation coefficient of 0.39(-0.37);while over the Yangtze River basin,the anomalous streamflow shows as positive in both EP and CP years,with correlation coefficients of 0.72 and 0.48,respectively.Analyses of the surface hydrological cycle indicate that the streamflow is more influenced by local evapotranspiration(ET)than precipitation over the Yellow River basin,while it is dominantly affected by precipitation over the Yangtze River basin.The different features over these two river basins can be explained by the anomalous atmospheric circulation,which is cyclonic(anticyclonic)north(south)of 30°N over East Asia.EP years are dominated by two anticyclones,which bring strong water vapor convergence and induce more precipitation but less ET,and subsequently increase streamflow and flooding risks.In CP years,especially over the Yellow River basin,two cyclones dominate and lead to water vapor divergence and reduce moisture arriving.Meanwhile,the ET enhances mainly due to local high surface air temperature,which further evaporates water from the soil.As a result,the streamflow decreases,which will then increase the drought risk.     

Low Frequency Streamflow Regimes over the Central United States: 1939–1998

Intra- to multi-decadal (6–30 year) streamflow regimes over the central United States during the late 20th century are identified and investigated here through a two-stage analysis. The first stage ranks mean annual flow rates during 1939–1998, calculates Mann–Whitney Ustatistics from samples of those rankings over running time windows, and then tests those U statistics for significance. This analysis of the records of 42 Hydro-Climatic Data Network stations over the Great Plains and Midwest reveals consistent patterns of highly ranked annual streamflow during time windows at the end of the century, with most beginning during the late 1960s and early 1970s and ending in either 1997 or 1998. Many of these stations are located in a critical agricultural region known as the Corn Belt. The second stage of analysis compares both the duration of abnormal flow periods and the frequency of hydrological surplus and drought conditions during the high flow years indicated by the first stage, relative to the remaining years of 1939–1998. Among gage stations in the climatologically drier western Corn Belt during the 1980s and 1990s there is a clear tendency toward extended periods of above normal flow, which results in more than a doubling in the average annual frequency of hydrological surplus days relative to previous years. These stations also show more than a 50% reduction in the average annual frequency of hydrological drought days relative to previous years. Similar but less pronounced shifts in hydrological regime are evident in the central and eastern Corn Belt, and in the Mississippi River at Vicksburg during 1973–1998. These results indicate that many areas of the central United States have shifted toward a climate regime of relative hydrological surplus during the closing decades of the 20th century.     

WRF/Chem模式中两种起沙参数化方案对东亚地区一次强沙尘暴过程模拟的影响

利用耦合了GOCART和Shao04两种起沙参数化方案的WRF/Chem模式对2002年3月19~22日发生在东亚地区的强沙尘暴过程进行模拟,着重考察了不同起沙方案对沙尘暴过程模拟的影响。结果表明,耦合了两种不同方案的WRF/Chem总体上均能较合理地模拟出主要的起沙区域、起沙强度的变化以及沙尘浓度的时空演变特征,模式对沙尘源地附近及下游地区地面沙尘浓度时间变化特征的模拟与站点观测结果也十分接近。但总体说来Shao04方案对沙尘起沙的发生以及强度变化过程具有更好的模拟能力,该方案模拟的沙尘浓度与观测更为一致,整体性能要优于GOCART方案。进一步分析发现,由于GOCART方案中采用的临界起沙风速偏小,导致该方案下模拟的沙尘分布范围偏大;另外该方案忽略了蒙古东南部和内蒙古中东部的潜在沙尘源地,从而使得耦合了GOCART方案的模式未能模拟出上述区域的起沙过程,使得该区域及下游地区模拟的沙尘浓度也偏小。但在塔里木盆地,Shao04方案计算的起沙通量偏小,这可能与Shao04方案未能考虑风速较小情况下空气拖曳力夹卷作用对起沙的影响有关,也可能与该方案中采用的土壤质地数据不准确有关。     

大渡河流域积雪特征及其与气候要素和径流的关系

利用MOD10A2遥感影像提取大渡河流域2010~2014年积雪覆盖数据,结合水文气象站点数据分析了大渡河流域积雪时空分布特征及气象因子-积雪面积-径流之间的关系。结果表明:年平均积雪面积最大的是康定,最小的是泸定。积雪在冬季最大,夏季积雪最少。积雪面积变化随月份起伏明显,积雪过程集中在10月到次年4月。降水和气温变化较一致,其峰值滞后于积雪面积峰值。积雪和气温、降水的相关性表明,积雪面积与气温、降水呈负相关,且气温与积雪面积相关性更大。径流的变化具有周期性,5月开始迅速增大,7月达到最大值。径流和积雪以及气象因子的相关性分析表明,径流与积雪面积呈负相关,与气温和降水都是正相关,且径流与降水相关性更大。      

Catchment precipitation processes in the San Francisco valley in southern Ecuador: combined approach using high-resolution radar images and in situ observations

The precise estimation of precipitation quantities in tropical mountain regions is in great demand by ecological and hydrological studies, due to the heterogeneity of the rainfall distribution and the lack of meteorological station data. This study uses radar images and ground station data to provide the required high-resolution precipitation maps. Also wind data are taken into account, due to its influence on the precipitation formation and to demonstrate the relation between synoptic wind, topography and the precipitation distribution inside small mountain valleys. The study analyses the rainfall distribution and amounts of 4 days inside the San Francisco Valley, a small catchment in the tropical Andes of southern Ecuador, representing different seasons and the typical atmospheric flows, which are correlated to the annual precipitation map. The results show that the rainfall distribution and amounts are generally defined by the wind direction and velocity, besides the topographic location in relation to the main barriers and pathways. The dominant wind direction causes a division of the catchment in a wetter eastern and a dryer western part. Moreover, the annual seasons are reversed; the main rainy season for the eastern part occurs between June and August, while the western part reaches the precipitation maximum between January and March. This may have influence on the species composition at the different slopes and the annual hydrological cycle inside the catchment.