Lowland catchment runoff response to climate change under CMIP6 in the Baltic region

Abstract. The geophysical and hydrological processes governing river flow formation exhibit persistence at several timescales, which may manifest itself with the presence of positive seasonal correlation of streamflow at several different time lags. We investigate here how persistence propagates along subsequent seasons and affects low and high flows. We define the high-flow season (HFS) and the low-flow season (LFS) as the 3-month and the 1-month periods which usually exhibit the higher and lower river flows, respectively. A dataset of 224 rivers from six European countries spanning more than 50 years of daily flow data is exploited. We compute the lagged seasonal correlation between selected river flow signatures, in HFS and LFS, and the average river flow in the antecedent months. Signatures are peak and average river flow for HFS and LFS, respectively. We investigate the links between seasonal streamflow correlation and various physiographic catchment characteristics and hydro-climatic properties. We find persistence to be more intense for LFS signatures than HFS. To exploit the seasonal correlation in the frequency estimation of high and low flows, we fit a bi-variate meta-Gaussian probability distribution to the selected flow signatures and average flow in the antecedent months in order to condition the distribution of high and low flows in the HFS and LFS, respectively, upon river flow observations in the previous months. The benefit of the suggested methodology is demonstrated by updating the frequency distribution of high and low flows one season in advance in a real-world case. Our findings suggest that there is a traceable physical basis for river memory which, in turn, can be statistically assimilated into high- and low-flow frequency estimation to reduce uncertainty and improve predictions for technical purposes.

River runoff components change variably and respond differently to climate change in the Eurasian Arctic and Qinghai-Tibet Plateau permafrost regions

We examined microhabitat selection by the Gulf sturgeon Acipenser oxyrinchus desotoi a subspecies of Atlantic sturgeon that is listed as threatened by the U.S. government. Individuals and groups of sturgeons were placed in a Ferguson flume at low (4–6 cm/s) and high (5–17 cm/s) water flows, and their distributions relative to substrate and water velocity were recorded with a video camera. A Jacobsˈ selectivity index (D) was used to evaluate substrate and velocity preference by the fish. Distribution of individual fish, relative to water velocity, differed significantly in the low (X2 = 11.8, df = 2, P < 0.05) and high (X2 = 39.0, df = 12, P < 0.05) water flows. Groups also selected velocities within low (X2 = 36.1, df = 2, P < 0.05) and high (X2 = 63.8, df = 12, P < 0.05) flows. Individual fish did not select substrates in low flow but moderately preferred cobble (D = 0.32) in high flow. Groups moderately preferred sand (D = 0.40) and moderately avoided cobble (D = –0.47) in low flow. No selection was observed by groups in high flow. Differences in use of substrate types by individual fish were not significant in low flow (X2 = 4.43, df = 2, P ≥ 0.05); however, the differences were significant in the other treatment combinations (group, low flow: X2 = 134.2, df = 2, P < 0.05; group, high flow: X2 = 21.05, df = 2, P < 0.05; individual, high flow: X2 = 11.03, df = 2, P < 0.05). Results from this laboratory experiment have implications for future microhabitat studies and represent the first quantified look at microhabitat selection by age-0 Gulf sturgeons.

Climate change effects on indicators of high and low river flow across Great Britain

The impacts of climate change on the seasonality of extremes i.e. both high and low flows in the Columbia River basin were analyzed using three seasonality indices, namely the seasonality ratio (SR), weighted mean occurrence day (WMOD) and weighted persistence (WP). These indices reflect the streamflow regime, timing and variability in timing of extreme events respectively. The three indices were estimated from: (1) observed streamflow; (2) simulated streamflow using simulated inputs from ten combinations of CMIP5 inputs for the future climate (2040–2070) including the pathway RCP4.5 (3) simulated streamflow using simulated inputs from ten combinations of CMIP5 inputs for the future climate (2040–2070) including the pathway RCP8.5. The hydrological model was calibrated at 1/16 latitude-longitude resolution and the simulated streamflow was routed to the subbasin outlets of interest. These three cases are compared to assess the effects of forcing by different climate models and different pathways on the three indices. The results showed significant differences between three cases indicating a shift in streamflow regime and timing of extreme events such as high and low flows in the Columbia River Basin. The persistence of high flows are similar in all cases. The results will help to understand the effects of climate change on three important seasonality properties: regime, timing and persistence and associated errors. Conclusion Multi-model Averaging of 10 Climate Forcing Data Results: Climate change impacts on high flows (Q90) Acknowledgment  High flows occur between mid-April and June: ~day 100th and 180 respectively in Fig 2  Winter low flows are observed in snow dominated northern and southeastern CRB where precipitation is kept as snow or ice in winter (Fig 2).  High flow persistence is increasing in all six locations by 2040s (Table 1)  No significant difference was found between RCP45 and 85 for WP  SR is increasing in all locations except for Revelstoke  Weighted mean high flow occurrence day (WMOD) is about ten day late as compared to observed WMOD of high flows. The delay is 20 days in Orofino by 2040s based on RCP85 scenario The Seasonality Ratio (SR): This index reveals the streamflow characteristics in summer and winter periods. The definitions of extremes (high or low flow) and the seasons (months for winter and summer) are crucial for the SR results as the underlying hydrological processes for summer and winter streamflows are different. In this study we focus on high flows and use the 90% exceedence probability (Q90) as a threshold for defining summer high flow (Q90s) and winter high flow (Q90w). The SR index is calculated as the ratio of Q90s and Q90w (Eq 4) A value of SR greater than one indicates the presence of a winter high flow regime and a value smaller than one indicates the presence of a summer high flow regime. Weighted Mean Occurrence Day (WMOD) The days at which the discharge is above the Q90 threshold are transformed into Julian dates Di, i.e. the day of the year ranging from 1 to 365 in regular years and 1 to 366 in leap years. The day number of each high flow event (Di) is weighted by the inverse high flow value (1/Qi) on the same day to address the severity of a high flow event as well as its occurrence day. The weighted mean day of occurrence is estimated first in radians to represent the annual cycle correctly. Otherwise, a simple averaging of high flow occurrences in winter months, e.g. January and December, can lead to a large error in the results. The weighted mean of Cartesian coordinates xθ and yθ of a total of high flow days i is defined as The values of θ can vary from 0 to 2π, where a zero value indicates the 1st of January, π/2 represents the 1st of April, pi represents the 1st of July and 3π /2 represents the 1st of October. The main advantage of using circular statistics is that it allows us to correctly average high flow occurrences in the winter half-year period. The WMOD is then obtained by back-transforming the weighted mean angle to a Julian date: (4)

Multivariate statistical methods, such as principal components analysis (PCA), discriminant analysis (DA) and general linear models (GLM) were applied to incorporate physico-chemical surface water quality in low and high flow hydrology in Northern Iran, based on analysis of the 7-day low flow index and existing water quality data. In view of this, 7-day low flows were calculated for 15 water years (1991–2006) at 15 monitoring stations. Eleven water quality parameters were extracted during the low flows from the water quality data and compared to water quality during high flows. Significant differences in water quality were noted for some monitoring stations and the pattern and magnitude of the statistically significant responses (t test, p < 0.05) varied among sites. PCA, was applied to the data sets of the two low and high flow periods, and resulted in three effective factors explaining 77.8 and 67.4 % of the total variance in surface water quality data sets of the two periods, respectively. The main factors obtained from PCA indicated that the parameters influencing surface water quality are mainly related to natural, point and non-point source pollution in the study area. DA provided an important data reduction as it used only three parameters, i.e. magnesium (Mg2+), calcium (Ca2+) and bicarbonate (HCO3 −) affording 60 % correct assignations, to discriminate between the two low and high stream flow periods. General regression models revealed that surface water quality parameters were explained by low and high flow and specific discharge. The results of this study can be useful for water managers for effective surface water quality management under climate change.

A number of extensive droughts and destructive floods have occurred in Poland in the last 25 years; hence, projections of low and high river flows are of considerable interest and importance. In the first part of this paper, projections of low and high flows in the rivers of the Vistula and the Odra basins (VOB region), for two future time horizons, are presented. Projections are based on the Soil and Water Assessment Tool (SWAT) hydrological model simulations driven by results of the EURO‐CORDEX experiment under Representative Concentration Pathways 4.5 and 8.5. The VOB region covers most of Poland and parts of five neighboring countries, giving this study an international relevance. In the second part of the paper, a review of projections of low and high flows in rivers in Central and Eastern Europe is presented. Despite a substantial spread of flow projections, the main message of the modelling part is that increases of both low and high flows are dominating. The magnitude of increase of low flow is considerably higher than that of high flow. In other words, future streamflow droughts are projected to be less severe, whereas, in contrast, river floods are projected to increase, which is a challenge for flood risk reduction, water management, and climate change adaptation. There is an overall agreement of our findings for the VOB region with projections of hydrological extremes from large‐scale models forced by EURO‐CORDEX results in the European‐scale studies.

Exceptionally low river flows are predicted to become more frequent and more severe across many global regions as a consequence of climate change. Investigations of trace metal transport dynamics across streamflows reveal stark changes in water chemistry, metal transformation processes, and remediation effectiveness under exceptionally low-flow conditions. High spatial resolution hydrological and water quality datasets indicate that metal-rich groundwater will exert a greater control on stream water chemistry and metal concentrations because of climate change. This is because the proportion of stream water sourced from mined areas and mineralized strata will increase under predicted future low-flow scenarios (from 25% under Q45 flow to 66% under Q99 flow in this study). However, mineral speciation modelling indicates that changes in stream pH and hydraulic conditions at low flow will decrease aqueous metal transport and increase sediment metal concentrations by enhancing metal sorption directly to streambed sediments. Solute transport modelling further demonstrates how increases in the importance of metal-rich diffuse groundwater sources at low flow could minimize the benefits of point source metal contamination treatment. Understanding metal transport dynamics under exceptionally low flows, as well as under high flows, is crucial to evaluate ecosystem service provision and remediation effectiveness in watersheds under future climate change scenarios.

Low and high flows are associated with different hydrological processes. High flows correspond to the direct response of catchments to water input, whereas low flows occur in pronged dry periods and are governed by depleting storages. Therefore, the inter‐annual dynamics of high and low flows are often considered to be independent. To shed light on this assumption, we analysed a pan‐European dataset of 615 streamflow records, summarized as time series of annual streamflow percentiles (5th, 10th, …, 95th). The analysis was based on comparing the spatial cross‐correlation patterns derived from the different percentile series. Their interrelation was visualized by projecting them into a low‐dimensional space. We found that large parts of the cross‐correlations of the percentile series can be summarized by one dominating component. This component represents geographical continuous regions in Europe of correlated streamflow. Departures from this mean pattern occurred for low and high flows and were characterized by the corresponding spatial correlation functions. Generally, spatial correlations appear to be stronger for high flows than for mean flows, particularly for short distances (&lt;400 km). Low flows, on the other hand, have the lowest spatial correlations for short distances. For longer distances (&gt;800 km), this pattern reverses and the spatial correlation of low flows become largest. This discrepancy between low and high flows suggests that hydrological systems are more homogeneously linked to climatic fluctuations under wet conditions. Under dry conditions, local catchment properties appear to play a larger role in translating climatic fluctuations into hydrological response. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Land cover has been increasingly recognized as an important factor affecting hydrologic processes at the basin and regional level. Therefore, improved understanding of how land cover change affects hydrologic systems is needed for better management of water resources. The objective of this study is to investigate the effects of land cover change on the duration and severity of high and low flows by using the Soil Water Assessment Tool model, Bayesian model averaging and copulas. Two basins dominated by different land cover in the Ohio River basin are used as study area in this study. Two historic land covers from the 1950s and 1990s are considered as input to the Soil Water Assessment Tool model, thereby investigating the hydrologic high and low flow response of different land cover conditions of these two basins. The relationships between the duration and severity of both low and high flow are defined by applying the copula method; changes in the frequency of the duration and severity are investigated. The results show that land cover changes affect both the duration and severity of both high and low flows. An increase in forest area leads to a decrease in the duration and severity during both high and low flows, but its impact is highest during extreme flows. The results also show that the land cover changes have had significant influences on changes in the joint return periods of duration and severity of low and high flows. While this study sheds light on the role of land cover change on severity and duration of high and low flow conditions, more studies using various land cover conditions and climate types are required in order to draw more reliable conclusions in the future. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Apalachicola Bay, an estuary located in northwest Florida, is likely to experience a continuing increase in the severity of the effects of changing climate and human-induced stressors, such as sea level rise and changes in freshwater inflow. A coupled hydrodynamic and food web modeling approach was used to simulate future scenarios of freshwater input and sea level rise in Apalachicola Bay from 2020 to 2049 to demonstrate the range of temporal and spatial changes in water temperature, salinity, fisheries species biomasses, total food web biomass and upper trophic level diversity. Additionally, a survey of Apalachicola Bay stakeholders was conducted concurrently with model development to assess stakeholder knowledge and concerns regarding species and environmental changes within the system. Results of the model simulations indicated an increase in water temperature across all scenarios and an increase or decrease in salinity with scenarios of low or high river flow, respectively. These results aligned with the impacts anticipated by stakeholders. White shrimp biomass increased with low river flow and decreased with high river flow, while Gulf flounder biomass decreased across all scenarios. The simulated trends in white shrimp biomass contrasted with stakeholder perceptions. The food web model results also showed an increase in total food web biomass and decrease in upper trophic level diversity across all future scenarios. For all modeled simulations, the largest differences in future environmental variables and species biomasses were between scenarios of low and high river flow, rather than low and high sea level rise, indicating a stronger influence of river flow on the abiotic and biotic characteristics of the estuary. Stakeholders anticipated a future reduction in river flow and increase in sea level rise as negatively impacting the Franklin County economy and stakeholders’ personal interaction with the Apalachicola Bay ecosystem. The use of the ensemble modeling approach combined with the stakeholder survey highlights the use of multiple knowledge types to better understand abiotic and biotic changes in the estuarine system. Results provide insight on the synergistic effects of climate change and human-induced stressors on both the estuarine food web and human community of Apalachicola Bay.

Research Article| January 01, 2014 The importance of erosion in distributary channel network growth, Wax Lake Delta, Louisiana, USA John B. Shaw; John B. Shaw Jackson School of Geosciences, University of Texas at Austin, C9000, Austin, Texas 78712, USA *Current address: Department of Geology and Geophysics, University of Wyoming, Department 3006, Laramie, Wyoming 82071, USA. Search for other works by this author on: GSW Google Scholar David Mohrig David Mohrig Jackson School of Geosciences, University of Texas at Austin, C9000, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Author and Article Information John B. Shaw *Current address: Department of Geology and Geophysics, University of Wyoming, Department 3006, Laramie, Wyoming 82071, USA. Jackson School of Geosciences, University of Texas at Austin, C9000, Austin, Texas 78712, USA David Mohrig Jackson School of Geosciences, University of Texas at Austin, C9000, Austin, Texas 78712, USA Publisher: Geological Society of America Received: 20 May 2013 Revision Received: 11 Sep 2013 Accepted: 12 Sep 2013 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2013 Geological Society of America Geology (2014) 42 (1): 31–34. https://doi.org/10.1130/G34751.1 Article history Received: 20 May 2013 Revision Received: 11 Sep 2013 Accepted: 12 Sep 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John B. Shaw, David Mohrig; The importance of erosion in distributary channel network growth, Wax Lake Delta, Louisiana, USA. Geology 2014;; 42 (1): 31–34. doi: https://doi.org/10.1130/G34751.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A river delta’s shape and kinematics are dictated by the three-dimensional evolution of its distributary channels on the delta front, yet measurements of this evolution are scarce. We supply four bathymetric surveys documenting this evolution for Gadwall Pass—part of the Wax Lake Delta, one of the few rapidly prograding regions of the greater Mississippi Delta in coastal Louisiana, United States. This distributary channel extends 2–6 km beyond the sub-aerially emergent delta (dependent on water surface elevation) and bifurcates into four similarly sized distributary channels (average channel width = ∼150 m) in this sub-aqueous reach. Distributary channel growth proceeds primarily through erosion of the unchannelized foreset deposit, and growth patterns differ between high and low river flow. During high river flow, high upstream sand supply acts to aggrade the bed both inside and outside of the channel network. Erosion during high flow is focused at the sand shoals that define the sidewalls of the bifurcate channels, causing channel network rearrangement into a single primary channel with the remaining secondary channels branching off of it. During low river flow, bed erosion is focused at channel tips and the beds of all of the subaqueous distributary channels, leading to a bayward extension of each channel tip by ≥0.87 channel-widths. Channel-bottom erosion during low river flow is enhanced by tidally modulated currents that support sand suspension and transport in the subaqueous channels during ebb tide while receiving only a small sand supply from upstream. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Upper Indus Basin (UIB) features the high mountain ranges of the Hindukush, Karakoram and Himalaya (HKH). The snow and glacier meltwater contribution feeds 10 major river basins downstream including Astore, Gilgit, Hunza, Jhelum, Kabul, Shyok and Shigar. Climate change is likely to fluctuate the runoff generated from such river basins concerning high and low streamflows. Widening the lens of focus, the present study examines the magnitude and timing of high flows variability as well as trends variability in low streamflows using Sen’s slope and the Mann-Kendall test in UIB from 1981 to 2016. The results revealed that the trend in the magnitude of the high flows decreased at most of the sub-basins including the Jhelum, Indus and Kabul River basins. Significantly increased high flows were observed in the glacier regime of UIB at Shigar and Shyok while decreased flows were predominant in Hunza River at Daniyor Bridge. A similar proclivity of predominantly reduced flows was observed in nival and rainfall regimes in terms of significant negative trends in the Jhelum, Kunhar, Neelum and Poonch River basins. The timing of the high flows has not changed radically as magnitude at all gauging stations. For the low flows, decreasing significant trends were detected in the annual flows as well as in other extremes of low flows (1-day, 7-day, 15-day). The more profound and decreasing pattern of low flows was observed in summer at most of the gauging stations; however, such stations exhibited increased low flows in autumn, winter and spring. The decrease in low flows indicates the extension of dry periods particularly in summer. The high-water demand in summer will be compromised due to consistently reducing summer flows; the lower the water availability, the lower will be the crop yield and electricity generation.

&amp;lt;p&amp;gt;&amp;amp;#160; &amp;amp;#160; &amp;amp;#160; &amp;amp;#160;In the area of Mt Gongga (Hengduan range, China) most glaciers are experiencing considerable retreat and mass loss since the early 20th century. Drainage of recently deglaciated surfaces delivers fine sediments thus affecting patterns of sediment delivery with impacts on water quality. Research in the area indicates significant differences between sediment at high flows and low flows in the same river during different seasons. High level flows were usually caused by heavy rainfall events or continuous rainfall that erode the slopes by sheet, rill and gully erosion and transport important amounts of sediments to streams leading to significant increases in river sediment flux. During low flows subsurface soil flux during spring and the direct discharge at the outlet of the glacier result in much less sediment load and mean suspended sediment concentration compared with high flows. The runoff volume, hydrograph peak, sediment load and mean suspended sediment concentration in high flows are as much as an order of magnitude higher than in low flows. Therefore, it is of great significance exploring the provenance of fine sediment during high flows and low flows to assess if there are differences in the contributing sources of sediments.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160; &amp;amp;#160; &amp;amp;#160; &amp;amp;#160; &amp;amp;#160; For this purpose during a 2 weeks field campaign in May 2016 in the frame of IAEA INT5153 project, source sediment samples and channel bed sediment mixtures were collected along the river valley of the Hailuogou Glacier. Three main sources were identified: surface glacier materials, old moraines and recent moraines. Composite surface samples (2 cm) were created of 10 subsamples in each representative site for surface glacier materials. Following the same scheme on old lateral moraines 10 sites were selected from the more mineral blocky deposits to the most vegetated parts at higher altitudes. On recent moraines 12 sites with different stages of vegetation cover were sampled. Starting from the glacier tongue a total of 7 fine sediment mixtures were collected along the river of which 3 composite samples corresponded to the dry season with low flow and 4 samples corresponded to high flow.&amp;amp;#160; A new consensus test method and an unmixing model were used to estimate the apportionments of the sediment sources to the sediment loads. The results showed that the contribution of different sources to the sediment mixture deposits varied along the river showing different provenance for the low and high flow suggesting different mechanisms of sediment generation during melting and dry seasons. This study is of interest for gaining knowledge on changing dynamics of sediment in regions were the rapid disappearance of glaciers and snow as in Mt. Gongga, has increased the mobilization and transport of sediment loads with consequences for the local population.&amp;lt;/p&amp;gt;

Quantifying impacts of land-use change on streamflow extremes is challenging, primarily due to the masking effects of other environmental processes. Our current understanding of these impacts on streamflow extremes remains incomplete. Here, we use explainable machine learning techniques to analyse over 1.5 million seasonal 7-day low-flow and high-flow events across 10,717 catchments worldwide between 1982 and 2023. Our model incorporates antecedent meteorological conditions, annual change of six land-use categories, and catchment characteristics (hydrogeological, anthropogenic, and topographic) as explanatory variables. The Shapley additive explanations technique is employed to quantify the contributions of the predictors to low and high flows. Our results indicate that all categories of land-use change exert a greater influence on high flows compared to low flows, although the overall contribution of land-use change to streamflow extremes is far smaller (&lt; 2%) than that of antecedent meteorological conditions (32%&amp;#8211;48%) and hydrologic signatures (35%&amp;#8211;52%). Contrary to previous studies, our results indicate that land-use impacts are largely independent of catchment size. Notably, urbanization exhibits diverging effects on low flows: enhancing them in arid regions, reducing them in tropical regions, and minimally impacting them in temperate regions. Urbanization nearly always amplifies high flows, except in minimally urbanised catchments of arid regions. Areas with higher forest cover consistently have smaller low flows across all climate zones, and high flows appear generally insensitive to afforestation. Low flows generally are insensitive to cropland expansion but areas with more cropland typically have smaller high flows.