Streamflow Trends Research Articles

Human-Induced Alterations to Land Use and Climate and Their Responses for Hydrology and Water Management in the Mekong River Basin

The Mekong River Basin (MRB) is one of the significant river basins in the world. For political and economic reasons, it has remained mostly in its natural condition. However, with population increases and rapid industrial growth in the Mekong region, the river has recently become a hotbed of hydropower development projects. This study evaluated these changing hydrological conditions, primarily driven by climate as well as land use and land cover change between 1992 and 2015 and into the future. A 3% increase in croplands and a 1–2% decrease in grasslands, shrublands, and forests was evident in the basin. Similarly, an increase in temperature of 1–6 °C and in precipitation of 15% was projected for 2015–2099. These natural and climate-induced changes were incorporated into two hydrological models to evaluate impacts on water budget components, particularly streamflow. Wet season flows increased by up to 10%; no significant change in dry season flows under natural conditions was evident. Anomaly in streamflows due to climate change was present in the Chiang Saen and Luang Prabang, and the remaining flow stations showed up to a 5% increase. A coefficient of variation <1 suggested no major difference in flows between the pre- and post-development of hydropower projects. The results suggested an increasing trend in streamflow without the effect of dams, while the inclusion of a few major dams resulted in decreased river streamflow of 6% to 15% possibly due to irrigation diversions and climate change. However, these estimates fall within the range of uncertainties in natural climate variability and hydrological parameter estimations. This study offers insights into the relationship between biophysical and anthropogenic factors and highlights that management of the Mekong River is critical to optimally manage increased wet season flows and decreased dry season flows and handle irrigation diversions to meet the demand for food and energy production.

Impact of rainfall variability and anthropogenic activities on streamflow changes and water stress conditions across Tapi Basin in India

Water security is a major concern in recent years, especially, in semi-arid and arid regions, which are adversely impacted due to extensive anthropogenic and climatic changes across the globe. Present study investigates the long-term changes in streamflows, their quantitative attribution and socio-environmental implications for a climatically sensitive Tapi basin in west central India. The abrupt and gradual changes in streamflows have been detected over the period 1973–2013 using non-parametric Pettit's and Mann-Whitney U tests; and Modified Mann-Kendall, Spearman's Rho and Sen's slope estimator tests respectively. The streamflow analyses revealed heterogeneity across the basin, wherein the tributaries exhibited higher variability in annual runoff compared to the Tapi River. The spatial analyst tool of ArcGIS has been used to graphically demonstrate the spatial variability in rainfall and streamflow trends across the basin. The streamflows exhibited predominantly decreasing trends across the basin, except in the upper reaches of the Tapi River. The decreasing trends in streamflow are largely attributed to anthropogenic activities such as changes in the land use patterns viz., increase in agriculture area, construction of minor and medium hydraulic structures, decrease in forest cover, rapid urbanization, excessive groundwater extraction and streamflow regulations. The anthropogenic activities played a major role in declining streamflow trends in the Tapi basin, contributing about 68%–99% (average 85%) decline in total runoff, compared to rainfall variability, which contributed around 1%–32% (average 15%) decrease in total runoff. The analysis of water stress levels at sub-catchment scale exhibited significant rise in percentage of population living in the basin facing chronic water shortage (i.e., <1000 m3/capita/year), from 34.0% in year 1981 to 63.2% in year 2011, mostly in semi-arid regions. The reduction in water availability clearly highlighted the deteriorating water quality and stream ecology of the Lower Tapi River in Surat city, India.

Characterizing groundwater and surface-water interaction using hydrograph-separation techniques and groundwater-level data throughout the Mississippi Delta, USA

The Mississippi Delta, a portion of the Mississippi Alluvial Plain (MAP) located in northwest Mississippi (USA), is an area dense with industrial-level agriculture sustained by groundwater-dependent irrigation supplied by the Mississippi River Valley alluvial aquifer. Observed declines in groundwater-level elevations and streamflow, contemporaneous with increases in irrigation, have raised concerns about future groundwater availability and the effects of groundwater withdrawals on streamflow. To quantify the impacts of groundwater withdrawals on streamflow and increase understanding of groundwater and surface-water interaction in the MAP, hydrograph-separation techniques were used to estimate baseflow and identify statistical streamflow trends. The analysis was conducted using the US Geological Survey Groundwater Toolbox open-source software and daily hydrologic data provided by a spatially distributed network of paired groundwater wells and streamgage sites. This study found that statistically significant reductions in stream baseflow occurred in areas with substantial groundwater-level declines. The use of hydrograph-separation and trend analyses to quantify the impacts of groundwater withdrawals and the use of streamflow as a proxy for changes in groundwater availability may be applicable in other altered environments. Characterizing and defining hydrologic relations between groundwater and surface water will help scientists and water-resource managers refine a regional groundwater-flow model that includes the Mississippi Delta, which will be used to aid water-resource managers in future decisions concerning the alluvial aquifer.

Impact of Climate Change on Water Resources in Lower Niger Basin in Nigeria

The objective of this paper is to investigate the temporal trends of streamflow in the Lower Niger River Basin in Nigeria using Mann – Kendall (MK), Spearman’ rho (SP) and Thiel – Sen (TSA) non parametric tests at 5% of significant level. The effect of auto – correlation in the time series was eliminated using a Trend Free Pre – whitening (TFPW) approach .The results obtained show negative trends in annual maximum series and both deceasing and increasing trends in annual minimum series. The estimated slopes range -354.94£b£ -52.62m 3 /s/year and -0.92£b≤ 30m 3 /s/year for annual maximum and minimum series respectively. Both MK and SP tests showed consistent performance and ability in detection of trends at 5% significant level. The negative trends in streamflow combined with simultaneous decrease in rainfall and increase in air temperature are plausible evidence of climate change. Also, positive correlation between freshwater discharge and salinity intrusion into River Niger was observed. The combined effect of streamflow reduction and salinity intrusion will impact adversely on the agricultural potentials, water quality status and vegetation of the Lower Niger River Basin. Finally, this study recommends against construction of new reservoirs as this will exacerbate the observed negative trends, leading to unsustainable development. Keywords: Trend analysis, Climate change, Nigeria, Salinity intrusion, Mann – Kendall and Thiel – Sen Estimator. DOI : 10.7176/CER/11-4-02 Publication date :May 31 st 2019

Hydro-Climatic Variability: A Characterisation and Trend Study of the Awash River Basin, Ethiopia

The objective of this study was to characterize, quantify and validate the variability and trends of hydro-climatic variables in the Awash River Basin (ARB) in Ethiopia using graphical and statistical methods. The rainfall and streamflow trends and their relationships were evaluated using the regression method, Mann–Kendall (MK) test and correlation analysis. The analysis focused on rainfall and streamflow collected from 28 and 18 stations, respectively. About 85.7% and 75.3% of the rainfall stations exhibited normal to moderate variability in annual and June to September rainfall, respectively, whereas 96.43% of rainfall stations showed high variability in March to May. The MK test showed that most of the significant trends in annual rainfall were decreasing except in two stations. These research findings provide valuable information on the characteristics, variability, and trend of rainfall and streamflow necessary for the design of sustainable water management strategies and to reduce the impact of droughts and floods in the ARB.

Quantifying the Performances of the Semi-Distributed Hydrologic Model in Parallel Computing—A Case Study

The research features how parallel computing can advance hydrological performances associated with different calibration schemes (SCOs). The result shows that parallel computing can save up to 90% execution time, while achieving 81% simulation improvement. Basic statistics, including (1) index of agreement (D), (2) coefficient of determination (R2), (3) root mean square error (RMSE), and (4) percentage of bias (PBIAS) are used to evaluate simulation performances after model calibration in computer parallelism. Once the best calibration scheme is selected, additional efforts are made to improve model performances at the selected calibration target points, while the Rescaled Adjusted Partial Sums (RAPS) is used to evaluate the trend in annual streamflow. The qualitative result of reducing execution time by 86% on average indicates that parallel computing is another avenue to advance hydrologic simulations in the urban-rural interface, such as the Boise River Watershed, Idaho. Therefore, this research will provide useful insights for hydrologists to design and set up their own hydrological modeling exercises using the cost-effective parallel computing described in this case study.

Yukarı Fırat Havzasının Uzun Dönem Akım Eğilimlerinin Analizi

The Euphrates River Basin system is of vital importance for water, food, energy security in Turkey, Syria, Iraq and under adverse climate change impact. It is therefore this paper mainly focuses on the naturally changing trend in long term streamflow with temperature and precipitation on the Upper Euphrates Basin that lies in Turkey. Because of the complexity of the setting up a basin-wide comprehensive hydrological model in the basin which have several large dams under operation ,we mainly used “run off data” in the statistical regression and time series analyses to predict the long term streamflow trends. We conclude that the annual natural flow has decreased mainly due to natural factors not because of construction dams. Obtained long term precipitation and air temperature trends in study area support the obtained streamflow trends. Results obtained from this study indicate that collaborative approach on transboundary water management between riparian’s is an urgent need.

Projecting climate change impacts on hydrological processes on the Tibetan Plateau with model calibration against the glacier inventory data and observed streamflow

Analyzing the impacts of climate change on hydrology and future projections of water supplies is fundamental for the efficient management and planning of water resources in large river systems on the Tibetan Plateau (TP), which is known as the “water tower of Asia.” However, large uncertainties remain in the projections of streamflow and glaciers in these cryospheric catchments due to great uncertainties in climate change projection and modeling processes. In this work, we developed an extended Variable Infiltration Capacity (VIC) macroscale hydrological model (named VIC-CAS), which was coupled with glacier melting and glacier evolution schemes. A two-stage calibration procedure that used glacier inventory data and the observed streamflow was adopted to derive the model parameters. The calibrated VIC-CAS model was then used to assess the future change in glaciers and runoff using downscaled climate model data in the upstream regimes of the Yellow, Yangtze, Mekong, Salween, and Brahmaputra rivers on the TP. The results indicated that both temperature and precipitation were projected to increase, resulting in a greater than 50% decline of the glacier area by the end of the 21st century in the five catchments. Glacier runoff was already beyond its tipping point at the beginning of the 21st century with a greater than 20% loss of the glacier area except in the upstream of the Yangtze River, where glacier runoff was projected to decrease after the 2030 s. Annual streamflow was projected to increase significantly as a result of increased rainfall-induced runoff, compensating for the reduced glacier/snow melt water in the five major upstream river basins. The increasing rate of warm season streamflow was clearly less than that of annual runoff. A negative trend in warm season streamflow was expected if precipitation did not sufficiently increase. The annual hydrograph remained largely unchanged, except in the upstream of the Yellow River, where peak streamflow was predicted to occur 1 month earlier because of the earlier snowmelt and greater rainfall/precipitation ratio from May to June.

Reconstruction and evaluation of changes in hydrologic conditions over a transboundary region by a regional climate model coupled with a physically-based hydrology model: Application to Thao river watershed

The differences among countries in terms of physical features, governmental policies, priorities in short- and long-term water resources management may lead to conflicts in managing and sharing of water resources over the transboundary regions. Due to no formal data sharing agreement between countries, there has been usually no data availability at transboundary regions. In this study, a methodology, in which a physically-based hydrology model was coupled with a regional climate model, is proposed to reconstruct and evaluate hydrologic conditions over transboundary regions. For the case study, Thao river watershed (TRW), within Vietnam and China, was selected. The Watershed Environmental Hydrology (WEHY) model was implemented based on topography, soil, and land use/cover information which was retrieved from global satellite data resources. The watershed model-WEHY was first validated over the TRW, and then was used to reconstruct historical hydrologic conditions during 1950–2007. The results of this study suggest no significant trend in the annual streamflow over the target watershed. In addition, there is a time shift in the wet season between the upstream sector in China and the downstream sector in Vietnam over the TRW. The annual flow contribution from the upstream sector in China to the outlet of TRW is estimated to be around 66%, and the remaining 34% contribution comes from the downstream sector in Vietnam territory. Last but not the least, the annual flow as a function of return period varies not only with the return period but also as a function of the time window, reflecting the effect of the changing regime on the streamflows at the TRW. The evolution of the flow frequency through time is an evidence of the ongoing non-stationarity in the hydrologic conditions over TRW.

Analysis of trends in annual streamflow to the Arctic Ocean

AbstractThere is increasing interest in the magnitude of the flow of freshwater to the Arctic Ocean due to its impacts on the biogeophysical and socio‐economic systems in the north and its influence on global climate. This study examines freshwater flow based on a dataset of 72 rivers that either directly or indirectly contribute flow to the Arctic Ocean or reflect the hydrologic regime of areas contributing flow to the Arctic Ocean. Annual streamflow for the 72 rivers is categorized as to the nature and location of the contribution to the Arctic Ocean, and composite series of annual flows are determined for each category for the period 1975 to 2015. A trend analysis is then conducted for the annual discharge series assembled for each category. The results reveal a general increase in freshwater flow to the Arctic Ocean with this increase being more prominent from the Eurasian rivers than from the North American rivers. A comparison with trends obtained from an earlier study ending in 2000 indicates similar trend response from the Eurasian rivers, but dramatic differences from some of the North American rivers. A total annual discharge increase of 8.7 km3/y/y is found, with an annual discharge increase of 5.8 km3/y/y observed for the rivers directly flowing to the Arctic Ocean. The influence of annual or seasonal climate oscillation indices on annual discharge series is also assessed. Several river categories are found to have significant correlations with the Arctic Oscillation, the North Atlantic Oscillation, or the Pacific Decadal Oscillation. However, no significant association with climate indices is found for the river categories leading to the largest freshwater contribution to the Arctic Ocean.

Long‐term streamflow trends in Hawai'i and implications for native stream fauna

AbstractClimate change has fundamentally altered the water cycle in tropical islands, which is a critical driver of freshwater ecosystems. To examine how changes in streamflow regime have impacted habitat quality for native migratory aquatic species, we present a 50‐year (1967–2016) analysis of hydrologic records in 23 unregulated streams across the five largest Hawaiian Islands. For each stream, flow was separated into direct run‐off and baseflow and high‐ and low‐flow statistics (i.e., Q10 and Q90) with ecologically important hydrologic indices (e.g., frequency of flooding and low flow duration) derived. Using Mann–Kendall tests with a running trend analysis, we determined the persistence of streamflow trends through time. We analysed native stream fauna from ~400 sites, sampled from 1992 to 2007, to assess species richness among islands and streams. Declines in streamflow metrics indicated a general drying across the islands. In particular, significant declines in low flow conditions (baseflows), were experienced in 57% of streams, compared with a significant decline in storm flow conditions for 22% of streams. The running trend analysis indicated that many of the significant downward trends were not persistent through time but were only significant if recent decades (1987–2016) were included, with an average decline in baseflow and run‐off of 10.90% and 8.28% per decade, respectively. Streams that supported higher native species diversity were associated with moderate discharge and baseflow index, short duration of low flows, and negligible downward trends in flow. A significant decline in dry season flows (May–October) has led to an increase in the number of no‐flow days in drier areas, indicating that more streams may become intermittent, which has important implications for mauka to makai (mountain to ocean) hydrological connectivity and management of Hawai'i's native migratory freshwater fauna.

A long-term, temporally consistent, gridded daily meteorological dataset for northwestern North America

We describe a spatially contiguous, temporally consistent high-resolution gridded daily meteorological dataset for northwestern North America. This >4 million km2 region has high topographic relief, seasonal snowpack, permafrost and glaciers, crosses multiple jurisdictional boundaries and contains the entire Yukon, Mackenzie, Saskatchewan, Fraser and Columbia drainages. We interpolate daily station data to 1/16° spatial resolution using a high-resolution monthly 1971–2000 climatology as a predictor in a thin-plate spline interpolating algorithm. Only temporally consistent climate stations with at least 40 years of record are included. Our approach is designed to produce a dataset well suited for driving hydrological models and training statistical downscaling schemes. We compare our results to two commonly used datasets and show improved performance for climate means, extremes and variability. When used to drive a hydrologic model, our dataset also outperforms these datasets for runoff ratios and streamflow trends in several, high elevation, sub-basins of the Fraser River.

Tracking changes in nutrient delivery to western Lake Erie: Approaches to compensate for variability and trends in streamflow

Abstract Tracking changes in stream nutrient inputs to Lake Erie over multidecadal time scales depends on the use of statistical methods that can remove the influence of year-to-year variability of streamflow but also explicitly consider the influence of long-term trends in streamflow. The methods introduced in this paper include an extended version of Weighted Regressions on Time, Discharge, and Season (WRTDS) modeling that explicitly considers nonstationary streamflow by incorporating information on changes in the frequency distribution of daily measured streamflow (discharge) over time. Soluble reactive phosphorus (SRP) trends in annual flow-normalized fluxes (loads) at five long-term monitoring sites in the western Lake Erie drainage basin show increases of 109 to 322% over the period 1995 to 2015. About one-third of the increase appears attributable to increasing discharge trends, while the remaining two-thirds appears to be driven by changes in concentration versus discharge relationships reflecting higher concentrations for any given discharge during recent years. Trends in total phosphorus and three nitrogen parameters (total nitrogen, nitrate-nitrite, and total Kjeldahl nitrogen) at the 10 sites analyzed were much less pronounced, and commonly show decreases in concentration-discharge relationships accompanied by increases in discharge, resulting in little net change in total flux. Trends in monthly SRP fluxes and discharge, dissolved versus particulate fractions of nutrients, and N:P flux ratios were also evaluated. The methods described here provide tools to more clearly discern the effectiveness of nutrient-control strategies and can serve as ongoing measures of progress, or lack of progress, towards nutrient-reduction goals.

Mapping of Stream Flow Trends in Porsuk Basin Using GIS Environment

In this study, trends of minimum, average and maximum flows were investigated in Porsuk basin, which is a sub-basin of Sakarya basin and then changes in flows were mapped using Geographical Information Systems (GIS). In the study, in 10 flow gauging stations across the Porsuk basin, monthly average, maximum and minimum flow data is used covering the period 1961-2013 (53 years). When analyzing the distribution of observed trends in the basin, a trend has been observed in most of the river flows. A decreasing trend has been observed overall in the basin. Trends are generally decreasing over time except for a few stations. As a result, increasing trends are observed in the west part of the basin; while in the east part of the basin decreasing trends are observed. When average and maximum monthly flows are investigated, decreasing trends are observed in the stations except DSI-12182. Trend analysis of 10 flow gauging stations across the Porsuk basin is investigated by Mann-Kendall method. Trend distribution was made according to flow trends of basin by transferring Z values to GIS.

The long-term trends in hydro-climatology of the Dinder and Rahad basins, Blue Nile, Ethiopia/Sudan

This paper examines the long-term trends of streamflow, rainfall and temperature over the Dinder and Rahad River basins. Streamflow of the Rahad River showed significant increasing trends in both the annual and seasonal flows. There was no detectable change in the mean annual and seasonal flow patterns of the Dinder. However, the analysis of seasonal maxima suggested a shift towards decreased flows during the high flow period (August) and increased flows during the low flow period (November). The Dinder maxima of August decreased from 517 m3/s over the early part of the record (1972-1991) to 396 m3/s over the latest years (1992-2011). The mean annual temperature showed significant increasing trends at the rate of 0.24 and 0.30 C/decade in the examined stations. Rainfall showed no significant change. The result of this study suggests other factors than climate variability (e.g., land use and land cover changes) to be responsible for streamflow alterations.

The long-term trends in hydro-climatology of the Dinder and Rahad basins, Blue Nile, Ethiopia/Sudan

This paper examines the long-term trends of streamflow, rainfall and temperature over the Dinder and Rahad River basins. Streamflow of the Rahad River showed significant increasing trends in both the annual and seasonal flows. There was no detectable change in the mean annual and seasonal flow patterns of the Dinder. However, the analysis of seasonal maxima suggested a shift towards decreased flows during the high flow period (August) and increased flows during the low flow period (November). The Dinder maxima of August decreased from 517 m3/s over the early part of the record (1972-1991) to 396 m3/s over the latest years (1992-2011). The mean annual temperature showed significant increasing trends at the rate of 0.24 and 0.30 C/decade in the examined stations. Rainfall showed no significant change. The result of this study suggests other factors than climate variability (e.g., land use and land cover changes) to be responsible for streamflow alterations.

Hydrological impacts of climate change on the future streamflow of three unregulated catchments of the Australian hydrologic reference stations

A physically-based distributed hydrological model (BTOPMC) is adopted to assess the impact of climate-change on the hydrological-behaviour of three-contributing catchments of the Australian hydrologic reference stations (HRSs). Both historical and future streamflow trends are compared and discussed. Firstly, the BTOPMC-model was calibrated and validated based on the observed hydro-meteorological data from the three-catchments. The calibrated BTOPMC-model was then forced with the downscaled future climate signals from a multi-model ensemble of eight-GCMs of the CMIP5 under the RCP4.5 and RCP8.5 scenarios to simulate the future daily streamflow at the three-HRSs for the mid (2046-2065) and late (2080-2099) of the 21st-century. Nearly all GCMs predict a reduction-tendency in mean-annual rainfall and an increase in temperature and potential-evapotranspiration across the studied catchments. The mean annual-streamflow also shows reductiontendencies during the future-periods ranged between 26%-53% at Dingo-Road HRS, 10%-25% at Haystack-HRS and 6%-33% at Coggan-HRS relative to the control-run.

Streamflow Impacts of Management and Environmental Change in the Upper Wabash River Basin

AbstractIn recent years, there is an ongoing debate regarding the causes of observed streamflow change across the Midwest. In the Wabash River basin in Indiana, streamflow trends due to changes in ...

Trends of streamflow under climate change for 26 Brazilian basins

Abstract Changes in the climate system and the hydrologic regime strongly affect all water uses and human activity. The main goal of this study is to evaluate the impact of rainfall pattern change on streamflow for 26 Brazilian basins with hydropower plants. More precisely, the goal is to estimate the trends on average streamflow for the 2011–2100 period. The estimated trends result from the analysis of rainfall obtained from a possible climate scenario, among others. The annual average streamflow for this 90-year period is simulated and compared with records from 83 years of observations (1931–2013). Simulations were carried out using two rainfall-to-streamflow hydrological models: Soil Moisture Accounting Procedure (SMAP) and Stochastic Linear Model (SLM). Results from simulations show important impacts, namely, an increase of streamflow in the southern basins and a decrease in the northern basins. Such changes can lead to disastrous consequences, considering the historical exposure to floods and droughts in the southern and northeast regions, respectively. These findings, in addition to the recent severe drought events that have occurred in such regions, provide awareness of a new cycle of reform to the existing water policies and Brazilian institutional framework, which saw the completion of its first 20 years in 2017.

Trend Analyses of Seasonal Streamflows of the Tapi Basin

Information about basin scale climate change is very crucial for utilization, development, and planning of water. The Tapi basin is climatically sensitive. For policymakers, it is important that changes in individual seasons are elucidated. Any earlier study on streamflows of the Tapi basin mentioned in the literature review had not performed trend detection analyses of streamflows of the Tapi basin for four seasons by considering individual month streamflow volume values of given season. Thus, in the present study, trend detection analyses of seasonal streamflow volume time series (1979–2004) of five gauging stations of Tapi basin are carried out for four seasons by considering individual month streamflow volume values of given season. The streamflow data of five gauging stations is selected out of 20 as these are less affected by human activities. Magnitude of trend is assessed by using Sen’s slope (SS) test while statistical significance of trend is assessed by using Mann-Kendall (MK) test and MK with block bootstrapping approach (MKBBS) test for independent and dependent data, respectively. Innovative trend analysis plot and smoothing curve are used for supporting results of trend analysis. The results of the analyses show presence of statistically significant negative trends in winter streamflow volume time series of Burhanpur, Gopalkheda, Lakhpuri, and Yerli gauging stations. Statistically significant negative trends are also detected in pre-monsoon streamflow volume time series of Lakhpuri and Yerli gauging stations. Similarly, statistically significant negative trends are detected in monsoon streamflow volume time series of Gopalkheda and Yerli gauging stations. Statistically significant negative trend is detected in post-monsoon streamflow volume time series of Yerli gauging station as well. The results have shown statistically significant decreasing trends in seasonal streamflows of the gauging station(s) of the Tapi basin.