Low Flow Periods Research Articles

БЕЗДОЩОВІ ПЕРІОДИ В СУЧАСНИХ КЛІМАТИЧНИХ УМОВАХ ЯК ФАКТОР МЕЖЕННОГО СТОКУ НА РІЧКАХ ПІВДНЯ УКРАЇНИ

The concept of non-rainfall periods is used to assess the climatic conditions of agriculture and water management for relatively short periods of time. Non-rainfall periods are a criterion for dryness because they characterize the length of the period without effective precipitation. Now, the period of modern climate change is of scientific and practical interest, as the study of the whole process as a whole, and changes that occur in individual climatic characteristics, such as the formation and duration of non-rainfall periods. The magnitude of rainfall, the intensity of their precipitation, or their absence determine in essence the presence and duration of low flow periods on rivers. Particularly relevant is the study of factors in the formation of runoff of low flow periods in the South of Ukraine, which can also be characterized as a zone of insufficient water. The main source of filling for rivers in the low-water period of the year is primarily groundwater runoff, as well as rainfall, which enters the channel network through their infiltration into groundwater. Therefore, long non-rainy periods can lead to a decrease in the underground supply of rivers, and sometimes to their drying up. Based on the definition of the non-rainfall period, in the study, such periods were determined according to regular observations of precipitation for the warm season (April-October) 1991-2019 at 41 meteorological stations in southern Ukraine. To study the impact of the duration of non-rainfall periods on the groundwater regime used data from the directory “Groundwater Status” for 2021. As a result of the analysis of the initial data, information was obtained on the recurrence and total duration of non-rainfall periods in the study area. In the South of the country in the period under review, the number of such periods ranged from 1 to 10 per season. It should be noted that in some years no non-rainfall periods were detected at some stations. The maximum values of the total number of days in non-rainfall periods reached 161 days in 2018 in Rozdilna (Odesa region), 155 days in Nova Kakhovka (2011), 154 days in the Black Sea and Henichesk in 2012, 153 days in Odesa, Chernomorsk and Bekhtery (2019), 150 days in Belgorod-Dniester (1992). Synoptic analysis of weather conditions in 2015 and 2016 showed that the formation of the longest non-rainfall periods due to the predominance of anticyclonic weather for a month or more, resulting in September in some areas turned out to be the driest for the whole period of observations. Analysis of the dynamics of groundwater levels showed natural tendencies to reduce their level with increasing duration of non-rainfall periods, which may adversely affect the supply of rivers in the dry period in modern climatic conditions

Last two millennia of streamflow variability in the headwater catchment of the Yellow River basin reconstructed from tree rings

The headwater catchment of the Yellow River Basin (HCYRB) controls 35% of the streamflow of the Yellow River (YR) which faces increasing water shortages. To better understand streamflow variability in the region we require a better understanding of high and low flow characteristics. This study presents a new annual (Nov-Oct) streamflow reconstruction at the Tangnaihai station in the HCYRB for the last two millennia (159–2016 C.E.) using 12 tree-ring chronologies. The nested principal component regression model combined with the stepwise best subset selection method was proposed to improve the temporal length and model skill of reconstruction. The stepwise best subset selection method was presented to select the best principal components subset, instead of a confidence test, based on k-fold cross-validation error and Akaike’s information criteria (AIC). The model assessment results verify that the proposed model exhibits strong reconstruction skills. Besides, the magnitude and duration of both high and low flow periods were analyzed. The results show that (1) the significant high-flow periods are the early 3rd century, circa 300 C.E., early 13th century, 16th century and circa 1900 C.E., while the low-flow periods are the late 5th century and late 15th century; (2) the durations and magnitudes of low-flow periods are longer and larger than high-flow periods and the severities of high-flow periods are greater than low-flow periods. The reconstruction also suggests that a warm climate is more likely accompanied by a high-flow period and low-flow periods are more likely to occur in cold periods associated with the Asian Summer Monsoon and solar activity.

The influence of thermal cues on the reproductive phenology of Silver Shiner, Notropis photogenis.

Reproductive phenology and the length of the growing season vary in response to interannual environmental variability, with implications for population dynamics of freshwater fishes. Understanding the reproductive phenology of imperilled species in relation to environmental conditions is needed to better evaluate potential responses to changing environmental conditions, estimate future population dynamics and develop comprehensive recovery strategies. We examined Silver Shiner, a species listed as "Threatened" under Canada's Species at Risk Act, during spring 2018 and 2019 to better understand the reproductive phenology of the species at the northern edge of its range in Canada. The initiation of Silver Shiner spawning occurred on the descending limb of the hydrograph and was completed before the onset of the extended period of low summer flow. In addition, both the initiation and cessation of spawning occurred in response to a cumulative growing degree day base 5 (GDD5 ) cue, with logistic regression models indicating a 50% probability the population initiated and ceased spawning when GDD5 reached 68°C•days and 368°C•days, respectively. Logistic regression incorporating GDD5 effectively predicted spawning initiation and cessation, providing useful models for examining the impacts of alterations to the thermal regime on reproductive phenology and improving the ability to evaluate changes in the larval growth period. Furthermore, the models can facilitate the development of real-time estimates of spawning activity, and therefore ensure that disturbance to the species is minimized during the sensitive reproductive period.

Identification of the contributing area to river discharge during low-flow periods

Abstract. The increasing severity of hydrological droughts in the Mediterranean basin related to climate change raises the need to understand the processes sustaining low flow. The purpose of this paper is to evaluate simple mixing model approaches, first to identify and then to quantify streamflow contribution during low-water periods. An approach based on the coupling of geochemical data with hydrological data allows the quantification of flow contributions. In addition, monitoring during the low-water period was used to investigate the drying-up trajectory of each geological reservoir individually. Data were collected during the summers of 2018 and 2019 on a Mediterranean river (Gardon de Sainte-Croix). The identification of the end-members was performed after the identification of a groundwater geochemical signature clustered according to the geological nature of the reservoir. Two complementary methods validate further the characterisation: rock-leaching experiments and unsupervised classification (k-means). The use of the end-member mixture analysis (EMMA) coupled with a generalised likelihood uncertainty estimate (GLUE) (G-EMMA) mixing model coupled with hydrological monitoring of the main river discharge rate highlights major disparities in the contribution of the geological units, showing a reservoir with a minor contribution in high flow becoming preponderant during the low-flow period. This finding was revealed to be of the utmost importance for the management of water resources during the dry period.

Functional diversity of benthic macroinvertebrates regarding hydrological and land use disturbances in a heavily impaired lowland river

This paper proposes the exploration functional diversity of benthic macroinvertebrates to evaluate their response to hydrological and land use stressors in a semi-arid lowland river. We aim to assess dominant functional traits and their sensitivity to environmental drivers, and how functional diversity respond to anthropogenic ecosystem impacts. Environment was evaluated through physical-chemical characterization of water, substrate and hydrological indices. For riparian condition assessment, we applied the QBR index for riparian forest quality and hemeroby index for level of anthropogenic intervention on the landscape. Links between environmental variables (R), taxa distribution (L) and trait composition (Q) were examined with RLQ and combined with fourth-corner analysis. The principal disturbance gradient was related to discharge regulation overlapping with land use represented by hemeroby index. There was also a gradient related to the hydrological regime which alternates seasonal floods with low flow periods. Traits related to reproductive and dispersal strategies were the most influenced by disturbance gradients, both natural and anthropogenic. Functional diversity decrease in sites subject to water abstraction and with higher hemeroby levels. Our findings have been promising in order to the application of functional diversity for biomonitoring in the Dulce River. Hemeroby enables the identification of trending changes between land uses, as well as to identify threat contexts. Furthermore, hemeroby could be useful in diagnostic stages to propose biomonitoring sites, by setting areas with different anthropogenic intervention on the ecosystem.

Improvement of the Hydrodynamic Behavior and Water Quality Assessment of Al-Chibayish Marshes, Iraq

Al-Chibayish Marsh (CM) is considered as the major part of Central Marshes area of this marsh is 1050 Km². The water quality of these marshes is suffering from salt accumulation due to intensive dam construction, limited supply of water from sources, climate change impacts, and the absence of outlet flow from these marshes, specifically at low flow periods. So, the current research aims to assess and improve these marshes' hydraulic behavior and water quality and define the best location for outlet drains. Field measurements and laboratory tests were conducted for two periods (November 2020 and February 2021) to define the (TDS) concentrations at nine different locations. Samples were also examined for water's physical and chemical properties as pH, electrical conductivity, water temperature, dissolved oxygen, and turbidity. Simultaneously with the sampling process, the water depths were measured at 50 different locations within the marshes. Moreover, the observations of water quality parameters were analyzed for the previous ten years (2010-2020). Hydrodynamic and water quality simulations were conducted using (SMS-RMA2 and RMA4) software to specify the water depths and velocity variations and define the salt content distribution. The obtained results illustrated 4sediment and TDS and in the Central Marshes area in general and CM in specific. As well, numerical results showed that the use of these outlets would significantly improve water quality. The current outlets do not work, and they link the Euphrates River to the Chabayish Marsh.

Abstract 10554: One Year Follow-up After Resuscitated Cardiac Arrest Admitted For Emergency Coronary Angiography: A Prospective, Observational Registry

Introduction: Despite improvement of in-hospital survival rate after aborted sudden cardiac death (SCD), cerebral anoxia may have severe neurologic consequences and may impair long term outcome and quality of life of surviving patients. Methods: This prospective, observational and multicentre (Montpellier and Nimes) study included patients > 18 yo admitted in the cathlab for CA after aborted SCD between May 1, 2018 to May 31, 2020. Only patients who were discharged alive from hospital were evaluated. The primary end point was survival without neurological sequelae at one year follow-up defined by Cerebral Performance Category (CPC) of 1 or 2. Secondary end points included global mortality, NYHA functional class, neurologic evaluation at discharge, 3-months and 1 year follow-up using the CPC scale, and quality of life at 1 year using the QOLIBRI (Quality of LIfe after BRain Injury) questionnaire. Results: Among 143 patients included during the study period, 61 (43%) were discharged alive from hospital and 55 (90%) of them completed follow-up at 1 year. Patients were young (59.4 +/- 14.1), mainly male (77%), with few cardiovascular risk factors. Duration of no and low flow period was short (1.9 +/- 2.4 and 16.5 +/- 10.4 minutes respectively). For 93% of the surviving patients, an initial shockable rhythm (n=57) was observed and acute coronary syndrome (ACS) was diagnosed in 75% of them (n=46). At 1 year, survival rate without neurologic sequelae was 87% (n=48). There were few recurrences of rhythm disorder (5%) or ischemic event (4%). Patients with poor outcome were older (p=0.036), have lower body mass index (p=0.013) and a lower initial LVEF (p=0.046). During follow-up, neurological status improved in 37% of patients presenting sequelae at discharge and overall quality of life was globally satisfying for 66% of patients according to the QOLIBRI questionnaire. No death from cardiac cause was reported, and mean LVEF at 1 year was improved (51.5 ± 9.2 vs 47.5 ± 11.5, p < 0.01). Conclusion: Among patients admitted to the cathlab for aborted SCD, mainly related to ACS, less than half of them were alive at discharge. However, their 1-year survival rate without neurological sequelae was high and their overall quality of life was good.

Simulated longleaf pine (Pinus palustris Mill.) restoration increased streamflow—A case study in the Lower Flint River Basin

AbstractWater scarcity in the southeastern United States has increased in recent decades due to population growth, land use intensification and climate variability. Precipitation is relatively abundant, but declines in streamflow suggest a need to better manage water yield. Restoration of low‐density, frequent‐fire longleaf pine (Pinus palustris Mill.) woodlands, which once dominated the southeastern Coastal Plain, represents a possible strategy to increase water yield and mitigate water scarcity. The Flint River Basin has seen recent conflicts over water appropriations and lies within the historic range of longleaf pine. We used the Soil and Water Assessment Tool (SWAT) to evaluate the potential effect of longleaf pine restoration on streamflow in the Ichawaynochaway Creek, a major tributary of the Flint River. Parameters governing plant water use, for example, leaf area and leaf physiology, were adjusted to create a longleaf pine land cover. We simulated the conversion of ~95,000 ha of existing forest to longleaf pine, an increase from 3% to 35% of landcover in the basin. Modelled evapotranspiration was lower for longleaf pine compared with other forest types in the region, and conversion to longleaf pine increased annual water yield by 17.9 ± 1.6 mm, or 5.2%. Proportional changes in monthly streamflow were up to 74% higher during low flow periods, when in‐stream habitat is most vulnerable. Restoration of longleaf pine could be a promising way to mitigate water scarcity in the southeastern United States and adding flow during extreme droughts may prove vitally important for conserving imperilled aquatic organisms.

Responses of marine zooplankton indicators after five years of a dam rupture in the Doce River, Southeastern Brazil

Since November of 2015, when ore tailings from a dam rupture reached the Atlantic Ocean, researchers are trying to assess the degree of impact across the Doce River and adjacent coastal area. This study aims to use the zooplankton dynamics as a tool to evaluate the environmental impact in the coastal region, five years after the rupture, during periods of low and high river flow. Doce River flow varied from 49 to 5179 m3/s and structured the zooplankton community between periods of low and high river flow, but salinity and chlorophyll-a had stronger correlation with depth (r = 0.40 and − 0.40 respectively) than with the Doce River discharge variation along the sampling period (r < 0.2). On the other hand, inorganic particles in the water and total metal concentration (dissolved + particulate), used as tracers of the iron enriched tailing (Al, Cd, Cr, Cu, Fe, V), were correlated with fluvial discharge and showed to be the main factor driving the zooplankton community dynamics. For assessing the degree of environmental impact, we tested the ecological indexes for the zooplankton community. Margalef Richness, Pielou Evenness and Shannon-Wiener Diversity varied from 2.52, 0.40 and 1.39 (all registered during high river flow period) to 9.02, 0.85 and 3.44 (all registered during low river flow period), respectively. Along with those community indicators, we evaluated the response of representative taxonomical genera such as Paracalanus, Oikopleura and Temora, regarding the Doce River flow, and found population patterns that established a baseline for future monitoring in the region. Our results showed that the zooplankton community is more fragile when the river discharge is stronger, and this pattern is confirmed by all indicators tested.

Environmental flow assessment in the context of climate change: a case study in Southern Quebec (Canada)

Abstract Through a case study in Southern Quebec (Canada), the assessment of environmental flows in light of the effects of climate change is investigated. Currently, the 7Q2 flow metric (7-day average flow with a 2-year return period) is used for water abstraction management. Several flow metrics were calculated using flow time series simulated by a deterministic hydrological model (HYDROTEL) and climate change scenarios as inputs. Results were compared within homogeneous low flow regions defined using ascendant hierarchical clustering, for the 1990, 2020 and 2050 horizons and annual, summer and winter periods. The impact of each flow metric on the potential availability of physical habitat was analyzed using the wetted perimeter as a proxy. Results indicated that: (1) the increasing non-stationarity of simulated flow data sets over time will complicate the use of frequency analysis to calculate the 7Q2 flow metric; (2) summer low flow values are expected to be lower than winter low flows; and (3) flow-duration curve metrics like the LQ50 (median discharge value of the month with the lowest flow) may become relevant environmental flow metrics by 2050. Results question current water abstraction management tools and permit us to anticipate future local and regional issues during low flow periods.

Discharge and Temperature Controls of Dissolved Organic Matter (DOM) in a Forested Coastal Plain Stream

Streams in the southeastern United States Coastal Plains serve as an essential source of energy and nutrients for important estuarine ecosystems, and dissolved organic matter (DOM) exported from these streams can have profound impacts on the biogeochemical and ecological functions of fluvial networks. Here, we examined hydrological and temperature controls of DOM during low-flow periods from a forested stream located within the Coastal Plain physiographic region of Alabama, USA. We analyzed DOM via combining dissolved organic carbon (DOC) analysis, fluorescence excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC), and microbial degradation experiments. Four fluorescence components were identified: terrestrial humic-like DOM, microbial humic-like DOM, tyrosine-like DOM, and tryptophan-like DOM. Humic-like DOM accounted for ~70% of total fluorescence, and biodegradation experiments showed that it was less bioreactive than protein-like DOM that accounted for ~30% of total fluorescence. This observation indicates fluorescent DOM (FDOM) was controlled primarily by soil inputs and not substantially influenced by instream production and processing, suggesting that the bulk of FDOM in these streams is transported to downstream environments with limited in situ modification. Linear regression and redundancy analysis models identified that the seasonal variations in DOM were dictated primarily by hydrology and temperature. Overall, high discharge and shallow flow paths led to the enrichment of less-degraded DOM with higher percentages of microbial humic-like and tyrosine-like compounds, whereas high temperatures favored the accumulation of high-aromaticity, high-molecular-weight, terrestrial, humic-like compounds in stream water. The flux of DOC and four fluorescence components was driven primarily by water discharge. Thus, the instantaneous exports of both refractory humic-like DOM and reactive protein-like DOM were higher in wetter seasons (winter and spring). As high temperatures and severe precipitation are projected to become more prominent in the southeastern U.S. due to climate change, our findings have important implications for future changes in the amount, source, and composition of DOM in Coastal Plain streams and the associated impacts on downstream carbon and nutrient supplies and water quality.

The use of wetted perimeter as habitat proxy to assess environmental flows in Southern Quebec rivers (Canada)

Environmental flows assessment in eastern Canada, and particularly in the province of Quebec, is mainly based on hydrological assessment of historical data during low flow periods. The mean 7-day low flow with return periods of two (7Q2) and ten years (7Q10) are two flow metrics currently used by the Quebec Department of Environment and Fight against Climate Change to prescribe minimum flow and/or maximum water abstraction while maintaining the functions and health of riverine ecosystems. This study investigated the use of the wetted perimeter as an additional environmental flows assessment method. This tool can be used by water managers to maintain the availability of river habitats during low flow periods. Twenty flow metrics were computed for inter-annual, summer and winter periods, for 43 sites from 35 rivers, and analysed to study the changes in wetted perimeter with flow. In addition, the flow associated with maximum curvature (breakpoint) of the flow-wetted perimeter function (QMC) was analyzed. Results provided a better understanding of local changes of river hydraulics and possible aquatic habitat availability associated with different flow metrics. The relevance of using a wetted perimeter threshold (WPSQMC) combined with flow thresholds (Tennant method) was also discussed. The two “fair” Tennant flow thresholds, apart from the twenty flow metrics, would provide sufficient available habitat all year long with corresponding WPSQMC thresholds of 88% and 95% of the 43 river sites. The median discharge for August flow metric for summer and the median discharge for the month with the lowest flow metric value for winter (usually February), provided the highest wetted perimeter in relative terms (72% and 79% respectively of the river sites) compared to the WPSQMC threshold. Using the 7Q2 flow metric would mean maintaining sufficient available habitat for 50%, 60% and 72% of the river sites for respectively inter-annual, summer and winter periods. Considering the single WPSQMC threshold, its associated flow provided the highest values for 16% of the river sites and the second highest one for 9% of the river sites with a single seasonal flow metric value high enough for summer or winter. This study showed that the wetted perimeter is a tool providing additional information on both river morphology and changes in potential aquatic habitat as a function of flow for river sites with small catchment size and low mean annual flow values. Indeed, the wetted perimeter can be very useful in the overall assessment of environmental flows.

Climate Change and Water Exploitation as Co-Impact Sources on River Benthic Macroinvertebrates

Climate change can affect freshwater communities superimposing on other major stressors, such as water exploitation, with effects still poorly understood. The exacerbation of naturally-occurring periods of low flows has been reported as a major hydrological effect of water diversions, with severe impacts on river benthic macroinvertebrate communities. This study aimed at assessing long-term modifications of low-flow events in a large lowland Italian river possibly associated to climate change and the effects of these events, intensified by water withdrawals, on benthic macroinvertebrates. A 77-year dataset on daily discharge was thus analyzed through Mann-Kendall test and Sen’s method to investigate modifications of the main hydrological parameters. Moreover, macroinvertebrates were collected during the low-flow periods that occurred from 2010 to 2015 at three sites downstream of water withdrawals, representing three different conditions of hydrological impairment. After assessing possible differences in taxonomical and functional composition between sites and impairment conditions, redundancy analysis and ordinary least squares regression were performed to link benthos metrics to environmental (hydrological and physico-chemical) characteristics. An increase in the duration of the low-flow periods and reduced summer flows were detected on the long term, and the magnitude of low flows was significantly altered by water withdrawals. These hydrological features shaped both structural and functional characteristics of benthic assemblages, highlighting the need for a more environmentally-sustainable water resource management in the current context of climate change.

Diagnosis of marine waste at Praia de Navegantes/SC in periods of low and high flow of the Itajaí-Açu River

O lixo marinho tem contribuído consideravelmente para a poluição marinha e é uma das tendências globais para a questão ambiental. O lixo marinho causa impactos à biota, impactos econômicos, à pesca e à estética das praias, o que demonstra a importância em se estudar mais o tema e buscar alternativas para mitigar tais problemas. Desta forma, é necessária a realização de estudos que identifiquem a composição, abundância e o comportamento desses detritos diante das variáveis meteorológicas, afim de contribuir para que ações de prevenção e mitigação sejam realizadas de forma mais efetiva. O presente estudo teve como objetivo testar hipóteses relativas à composição e origem provável do lixo marinho na praia de Navegantes/SC, em dois regimes de vazão do Rio Itajaí-Açu, assim como avaliar a abundância de pellets plásticos. A vasta maioria do macrolixo encontrado foi formada por itens plásticos, em quantidade significativamente maior no regime de alta vazão. A origem mais provável dos itens observados foi dos usuários da praia, também significativamente maior no regime de alta vazão. Uma quantidade expressiva de pellets plásticos (&gt;20/m2) foi encontrada na praia, sem distinção entre os regimes de vazão. Esses resultados poderão contribuir para que os órgãos ambientais locais definam melhores estratégias e ações de prevenção e mitigação do lixo marinho, como por exemplo, a elaboração de uma coleção didática de lixo marinho como ferramenta de educação ambiental.

Kills in the Darling: assessing the impact of the 2018–20 mass fish kills on the fish communities of the Lower Darling–

Understanding the impacts of extreme events is essential to effective fisheries management. During the summer of 2018–19 millions of native fish died in Lower Darling–Baaka River adjacent to Menindee, New South Wales, Australia. Hypoxia during a period of protracted low flow, triggered by climatic events, was responsible for the fish kills. From June 2019 to March 2020, further broader-scale fish kills occurred throughout ~600 km of the Darling–Baaka River as disconnected refuge pools contracted and water quality deteriorated. This study examined the status of the remnant fish populations, compared the fish assemblage of the Menindee fish death reach with an unaffected reach and monitored change of the fish community over 18 months after the initial fish kills. Significantly lower abundances of Murray cod (Maccullochella peelii), bony herring (Nematalosa erebi), carp gudgeon (Hypseleotris spp.) and freshwater prawn (Macrobrachium australiense) were captured within the Menindee fish death reach compared with the unaffected reach. Varied responses were observed in species abundances within the affected reach in the 18 months after the initial fish kills, attributed to the various life-history traits and reproductive strategies. The results presented highlight a fish community in continued stress. Continued monitoring will guide and track the effectiveness of recovery management interventions in the region.

Seasonal Variation and Sources Identification of Dissolved Sulfate in a Typical Karst Subterranean Stream Basin Using Sulfur and Oxygen Isotopes

Karst water, which provides approximately 25% of the world's drinking water, is especially vulnerable to anthropogenic pollutants. To determine the variations between high and low flow periods and the sources of dissolved sulfate (SO42-) in small karst basins, SO42- concentrations, stable sulfur and oxygen isotopes (δ34S-SO4 and δ18O-SO4), and oxygen isotopes of water (δ18O-H2O) were investigated in surface and groundwaters, during the high and low flow seasons, within the Babu subterranean stream basin. Analysis showed that: ① the water samples that were directly impacted by acid mine drainage exhibited high SO42- concentrations (≥250 mg·L-1) and significant seasonal variation, while the seasonal variation of non-AMD-impacted water with low SO42- concentrations was not significant. ② During the high flow season, the mean δ34S-SO4 and δ18O-SO4 values of surface water were -10.5‰ and 4.7‰, respectively, and -11.5‰ and 1.3‰ during the low flow period; the mean values of δ34S-SO4 and δ18O-SO4 in groundwater samples were -2.9‰ and 7.1‰ during the high flow period, respectively, and -3.2‰ and 6.2‰ during the low flow period. Both surface and groundwater samples exhibited higher δ34S-SO4 and δ18O-SO4 values during the high flow period than during the low flow period. ③ The values of δ34S-SO4 in the surface and groundwater samples were relatively stable, indicating that the sources of SO42- at specific sampling sites were stable.④ The main sources of SO42- in surface and groundwaters were rain, sulfide, and gypsum, accounting for 13%, 40%, and 47%, respectively, of SO42- in samples taken from the basin outlet during the high flow season, and 18%, 39%, and 43%, respectively, in samples obtained during the low flow season.

Hydrological characteristics of Australia: relationship between surface flow, climate and intrinsic catchment properties

Streamflow and baseflow dynamics are driven by complex, interconnected catchment properties. A national study was conducted to assess the relationship between surface flow, climate and intrinsic catchment attributes in Australia. Subcatchments were delineated based on Horton's 5th stream order and were characterised by identifying parameters that influence streamflow and flood behaviour. Because observational datasets like rainfall and streamflow commonly have a non-normal distribution, the method of L-moments was applied to several time series. Surface hydrology and baseflow patterns were represented by twenty indices, which were statistically summarised via principal component (PC) analysis, yielding six PCs. Forty catchment descriptors from the themes of climate, topography, surface condition and hydrogeology were used to investigate their link with runoff patterns. Among these is the land surface value, a newly defined index incorporating soil properties and land use to estimate the capacity for water infiltration. All metrics were explored via correlation and regression analysis against the surface hydrology PCs and their influence on runoff discussed. The predictive skill of the regression models is improved when non-perennial waterways are excluded. Although rainfall characteristics dominate streamflow behaviour, topographical and surface conditions also greatly impact on runoff, especially during low-flow periods.

Evaluating the relationship between hydrological extremes and groundwater in Luvuvhu River Catchment, South Africa

Extreme hydrological events have been reported to be on an increase in terms of magnitude and frequency in southern Africa. Groundwater in this area plays a significant role in domestic water supply and agriculture. The aim of this study is to evaluate the relationship between groundwater levels and hydrological extremes in north-eastern South Africa. An index-based approach was used to determine the drought and flood events over the study period while the Water Table Fluctuation approach was used to determine groundwater recharge. Flow duration curves were further employed to determine the exceedance period of high and low flows in the study area. Mann-Kendall and Sequential Mann-Kendall were used to detect trends and the point of change. Both floods and drought were found to have occurred in the study area at different magnitudes, however both the Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSI) found that majority of these were not categorized as mild to near normal conditions. Specific yield determined using the simple linear regression method ranged between 0.04 and 0.06. Groundwater recharge estimates ranged between 1.1 and 11.5 % of mean annual rainfall ranging between 167–1000 mm/a. About 60 % of the stations (i.e. rainfall, streamflow, and groundwater) show significantly decreasing trend. This therefore indicates that there is a decreasing trend in groundwater levels, streamflow, and rainfall over the study area. Based on the trend analysis findings, it suggests that extreme events in the catchment influences groundwater resources.

Future changes in snowpack will impact seasonal runoff and low flows in Czechia

Study RegionCentral Europe, Czechia. Study FocusMountains are referred to as “water towers” because they substantially affect the hydrology of downstream areas. However, snow storages will decrease in the future due to the increase in air temperature which will affect streamflow regime. Main objectives of this study were 1) to simulate the future changes in snow for a large set of mountain catchments in Czechia, reflecting a wide range of climate projections and 2) to analyse how the snow changes will affect groundwater recharge, streamflow seasonality and low flows in the future. New Hydrological InsightsThe future hydrological projections showed a decrease in annual maximum SWE by 30 %–70 % in the study area until the end of the 21st century. Additionally, snowmelt was found to occur on average 3–4 weeks earlier. The results showed the large variability between individual climate chains and indicated that the increase in air temperature causing the decrease in snowfall might be partly compensated by the increase in winter precipitation. Changes in snowpack will cause the highest streamflow during melting season to occur one month earlier, in addition to lower spring runoff volumes due to lower snowmelt inputs. The future climate projections leading to overall dry conditions in summer are associated with both the lowest summer precipitation and seasonal snowpack. The expected lower snow storages might therefore contribute to more extreme low flow periods.

Simultaneous external validation of various cardiac arrest prognostic scores: a single-center retrospective study

BackgroundThis study aimed to compare and validate the out-of-hospital cardiac arrest (OHCA); cardiac arrest hospital prognosis (CAHP); non-shockable rhythm, unwitnessed arrest, long no-flow or long low-flow period, blood pH < 7.2, lactate > 7.0 mmol/L, end-stage chronic kidney disease, age ≥ 85 years, still resuscitation, and extracardiac cause (NULL-PLEASE) clinical; post-cardiac arrest syndrome for therapeutic hypothermia (CAST); and revised CAST (rCAST) scores in OHCA patients treated with recent cardiopulmonary resuscitation strategies.MethodsWe retrospectively collected data on adult OHCA patients admitted to our emergency department between February 2015 and July 2018. OHCA, CAHP, NULL-PLEASE clinical, CAST, and rCAST scores were calculated based on the data collected. The predictive abilities of each score were tested using the area under the curve (AUC) of the receiver operating characteristic (ROC) curve.ResultsWe identified 236 OHCA patients from computer-based medical records and analyzed 189 without missing data. In OHCA patients without bystander witnesses, CAHP and OHCA scores were not calculated. Although the predictive abilities of the scores were not significantly different, the NULL-PLEASE score had a large AUC of ROC curve in various OHCA patients. Furthermore, in patients with bystander-witnessed OHCA, the NULL-PLEASE score had large partial AUCs of ROC from sensitivity 0.8–1.0 and specificity 0.8–1.0.ConclusionsThe NULL-PLEASE score had a high, comprehensive predictive ability in various OHCA patients. Furthermore, the NULL-PLEASE score had a high predictive ability for good and poor neurological outcomes in patients with bystander-witnessed OHCA.