scholarly journals Changing Low Flow and Streamflow Drought Seasonality in Central European Headwaters

Water ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3575
Author(s):  
Vojtech Vlach ◽  
Ondrej Ledvinka ◽  
Milada Matouskova
Keyword(s):  
Kendall Test ◽  
R Package ◽  
Low Flow ◽  
Headwater Catchments ◽  
Low Flows ◽  
Seasonality Index ◽  
Apparent Shift ◽  
Summer Minimum ◽  
Increasing Temperature

In the context of the ongoing climate warming in Europe, the seasonality and magnitudes of low flows and streamflow droughts are expected to change in the future. Increasing temperature and evaporation rates, stagnating precipitation amounts and decreasing snow cover will probably further intensify the summer streamflow deficits. This study analyzed the long-term variability and seasonality of low flows and streamflow droughts in fifteen headwater catchments of three regions within Central Europe. To quantify the changes in the low flow regime of selected catchments during the 1968–2019 period, we applied the R package lfstat for computing the seasonality ratio (SR), the seasonality index (SI), mean annual minima, as well as for the detection of streamflow drought events along with deficit volumes. Trend analysis of summer minimum discharges was performed using the Mann–Kendall test. Our results showed a substantial increase in the proportion of summer low flows during the analyzed period, accompanied with an apparent shift in the average date of low flow occurrence towards the start of the year. The most pronounced seasonality shifts were found predominantly in catchments with the mean altitude 800–1000 m.a.s.l. in all study regions. In contrast, the regime of low flows in catchments with terrain above 1000 m.a.s.l. remained nearly stable throughout the 1968–2019 period. Moreover, the analysis of mean summer minimum discharges indicated a much-diversified pattern in behavior of long-term trends than it might have been expected. The findings of this study may help identify the potentially most vulnerable near-natural headwater catchments facing worsening summer water scarcity.

Changing low flow seasonality in Central European headwaters

2021 ◽  
Author(s):  
Vojtech Vlach ◽  
Ondrej Ledvinka ◽  
Milada Matouskova
Keyword(s):  
Flow Regime ◽  
R Package ◽  
Hydrological Drought ◽  
Low Flow ◽  
Significant Shift ◽  
Regime Changes ◽  
Seasonality Index ◽  
Long Term Trends ◽  
Summer Minimum ◽  
Hydrological Droughts

<p>In the environment of the changing climate in Central Europe, the seasonality and magnitude of low flow events and hydrological droughts are projected to change in the near future. Ongoing increases in the air temperature, rates of evaporation and decreasing snow cover will significantly affect the summer deficit volumes even in the rivers of humid montane and highland areas in mid-latitudes. However, what if the significant changes have already been happening during the last decades? Therefore, this research is focused on analysis of the variability and seasonality of low flow events and hydrological drought events in fifteen near-natural catchments along the Czech–German and Czech–Polish national borders. To quantify the low flow regime changes of the study regions in the last 52 years (1968–2019), we applied tools from the R package lfstat. The 30-year moving averages of seasonality ratio (SR) and the seasonality index (SI) were derived to address the degree of change in each catchment. Moreover, the 7-day and 30-day mean summer minimum discharges were computed, as well as the streamflow deficit volumes for every episode of hydrological drought. The results showed a continual increase in the proportion of summer low flow and drought events during the study period along with a significant shift in the average date of low flow occurrence towards the beginning of the year. The most marked shifts in low flow seasonality were found mainly in catchments with the average altitude 800–1000 m a. s. l. Conversely, the low flow regime in catchments above 1000 m a. s. l. and also in the catchments below 800 m a. s. l. remained nearly stable throughout the 1968–2019 period. Moreover, the analysis of 7- and 30-day mean summer minimum discharges indicated a much-diversified pattern in the behavior of long-term trends than it was expected.</p>

Low flow frequency analysis for stream with mixed populations

2015 ◽  
Vol 42 (8) ◽  
pp. 503-509 ◽  
Author(s):  
Mike Hulley ◽  
Colin Clarke ◽  
Ed Watt
Keyword(s):  
Frequency Analysis ◽  
Worked Examples ◽  
Low Flow ◽  
Flow Estimation ◽  
Low Flows ◽  
Record Length ◽  
Mixed Populations ◽  
Flow Frequency ◽  
Recommendations For Assessment

A methodology is developed for the estimation of annual low-flow quantiles for streams with annual low flows occurring in both the summer and winter. Since the low flow generating processes are different in summer and winter, independent seasonal analyses are required. The methodology provides recommendations for assessment of record length, randomness, homogeneity, independence and stationarity, as well as guidelines for distribution selection and fitting for seasonal distributions. The seasonal distributions are then used to develop the combined distribution for annual low flow estimation. Four worked examples of long-term Canadian hydrometric stations are provided.

scholarly journals Long-term and Two-period Analysis of Hydrologic Conditions of the South Edisto River

2017 ◽  
pp. 13-20
Author(s):  
Rebecca W. Berzinis
Keyword(s):  
South Carolina ◽  
Low Flow ◽  
Mean Flow ◽  
South Fork ◽  
The South ◽  
Period Analysis ◽  
Daily Streamflow ◽  
Low Flows ◽  
Significant Difference

The U.S. Geological Survey (USGS) long-term daily streamflow record at station 02173000 in Bamberg County, South Carolina on the South Fork Edisto River (Latitude 33°23’35”, Longitude 81°08’00” NAD27) spans from 1932 to 2015 and was used for this study. The Nature Conservancy’s Indicators of Hydrologic Alteration (IHA) software was used to analyze the entire record of hydrologic data as ecologically relevant parameters and to categorize the flows. A two-period analysis was conducted to evaluate whether a significant difference could be observed in historic flow data from 1932–1985 (period one) compared to 1986–2015 (period two). An extreme low flow was defined as an initial low flow below 10% of daily flows for the period. Over the entire 76-year period of record, 51 years had at least one occurrence of extreme low flows. A median of 4 days per year had occurrences of extreme flows in period one in contrast to a median of 60 days per year during period two. Annual precipitation totals were not correlated with the number of days per year with extreme low flows. The two-period analysis showed significant differences between period one and period two for monthly mean flow for February, April, May, and August, as well as for 1-day and 30-day minima and maxima values. The analysis calculated the 7Q10 (the lowest stream flow for seven consecutive days that would be expected to occur once in ten years) at 4.4 cubic meters per second (cms), which was -10.9% different from the most recently published estimate. Results presented in this study have shown that spring and summer flows in the South Fork Edisto are statistically significantly lower in period two compared to period one.

Climate elasticity of low-flows: the long-term impact of droughts

2020 ◽  
Author(s):  
Vazken Andréassian ◽  
Alban de Lavenne
Keyword(s):  
Low Flow ◽  
Long Term Memory ◽  
Term Memory ◽  
Climate Elasticity ◽  
Climate Anomalies ◽  
Linear Dependency ◽  
Low Flows ◽  
Model Free ◽  
Hydrogeological Characteristics

<p>The long-term memory of catchments (carried by their hydrogeological characteristics) has a considerable impact on low-flow dynamics. Here, we present an exploratory study on a large French dataset to characterize the climate elasticity of low-flows and understand its long-term dependency. The climate elasticity of catchments is a simple concept (almost model-free) that allows analyzing the linear dependency of streamflow anomalies to climate anomalies (Andréassian et al., 2016). Widely-used for average annual streamflow, we propose to extend this concept to annual minimum monthly flow anomalies (QMNA) in order to characterize the climate dependency of QMNAs. By introducing progressively the linear dependency to the climatic anomalies of previous years, we further characterize the long-term memory of low-flows for the catchments of our set.</p><p><strong>References</strong></p><p>Andréassian, V., Coron, L., Lerat, J., and Le Moine, N. 2016. Climate elasticity of streamflow revisited – an elasticity index based on long-term hydrometeorological records, Hydrol. Earth Syst. Sci., 20, 4503-4524.</p><p> </p>

scholarly journals Zmienność przepływów niżówkowych w wybranych zlewniach pogórskich i beskidzkich w latach 1988‑2017 = Variability of low flow in Polish Carpathians (foothills and Beskidy Mountains) catchments in the period 1988‑2017

2021 ◽  
Vol 93 (1) ◽  
pp. 5-25
Author(s):  
Witold Bochenek ◽  
Małgorzata Kijowska-Strugała
Keyword(s):  
Land Use ◽  
Forest Cover ◽  
Arable Land ◽  
Low Flow ◽  
Soil Permeability ◽  
Low Flows ◽  
Polish Carpathians ◽  
Continental Climate

Water flow in the Polish Carpathians was exemplified by long-term (1988‑2017) analysis of two foothill catchments (of the Skawinka and Stobnica) and two catchments in the Beskidy Mountains (of the Soła and Osława). The work allowed for the determination of the duration of low flows and outflow deficits in relation to changes in thermal and precipitation conditions, as well as land use and land cover. In the selected catchments, the 30-year period brought a decrease in the area of arable land and an increase in the area of grassland and forest. In addition built-up areas increased by 495% between 1990 and 2018. A greater susceptibility to the occurrence of total drought was noted for the Beskidy Mountains catchments, in which the duration of low flows and outflow deficit was greater than in the foothill catchments. At the same time, the mountain catchments proved less susceptible to the emergence of deep drought, on account of their higher levels of forest cover and levels of soil permeability. In regional terms, the durations of low flows and outflow deficits were greater in the catchments located in the eastern part of the Carpathians (those of the Stobnica and Osława), in line with this area’s intensified features of a continental climate.

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

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2778
Author(s):  
Francesca Salmaso ◽  
Giuseppe Crosa ◽  
Paolo Espa ◽  
Silvia Quadroni
Keyword(s):  
Climate Change ◽  
Benthic Macroinvertebrates ◽  
Water Resource Management ◽  
Ordinary Least Squares ◽  
Low Flow ◽  
Benthic Assemblages ◽  
Low Flows ◽  
Water Exploitation ◽  
Water Withdrawals

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.

scholarly journals Spatiotemporal changes to low flow and catchment storage following a step change rainfall decline in Southwest Western Australia

2020 ◽  
Author(s):  
Keith Smettem ◽  
Ning Liu ◽  
Richard Harper ◽  
John Ruprecht
Keyword(s):  
Land Cover ◽  
Western Australia ◽  
Agricultural Land ◽  
Low Flow ◽  
Deep Soil ◽  
Low Flows ◽  
Eucalyptus Forest ◽  
Flow Duration Curves ◽  
The Impact

<p>Understanding how summer low flows in a Mediterranean climate are influenced by climate and land use is critical for managing both water resources and in-stream ecohydrological health. The Eucalyptus forest ecosystems of southwestern Australia are experiencing a drying and warming climate, with a regional step decline in rainfall in the mid-1970s.  Reductions in catchment water storage may be exacerbated by the deep rooting habit of key overstorey species (>30 m has been reported), which can buffer against drought during dry years. Root exploitation of deep soil moisture reserves and/or groundwater can accelerate the long term decline in summer low flows, with a trend towards more ephemeral flow regimes. In contrast, conversion of forests to agricultural land in some catchments can lead to counter-trends of increased low flows due to a rise in groundwater pressure.  These are invariably associated with an increase in stream salinity as regolith stores of salt are mobilized. There has also been extennsive reforestation of farmland in some catchments. </p><p>In this study we perform a detailed analysis of changes to annual summer seven day low flow trends in perennial catchments and flow duration curves in ephemeral catchments across 39 catchments in south-western Australia that have long term records of runoff, rainfall and land cover.  Results showed that 15% of catchments exhibited increased low flows and 85% decreased flows or decreased flow days since the 1970s.  Significant downward step changes in low flows were observed in 17 catchments (44%). The earliest downward step changes occurred in three catchments between 1981-82 (a lag of one decade after the rainfall decline), with the most recent step changes for five catchments occurring in 2001-2004 (three decades after rainfall decline).  Eleven catchments were already ephemeral in the 1970s, but exhibited continued declines in the number of annual flow days over subsequent decades.  Step changes occur when groundwater becomes disconnected or reconnected to the stream invert, with disconnection associated with rainfall decline and vegetative water use.  </p><p>The statistical methods we used in this study can be applied to any catchment in order to aid land and water managers assess the impact of climate change and land cover manipulation on low flow response.</p>

951: “Experience in the Treatment of Low Flow Priapism”; A Novel, Easy and Effective Technique: A Long-Term, Binational, Multi-Institutional Study in 18 Patients Over 8 Years

2007 ◽  
Vol 177 (4S) ◽  
pp. 314-315
Author(s):  
Jose A. Medina Machuca ◽  
Jose A. Medina Coello ◽  
Hugo Manzanilla ◽  
Francisco A. Gutierrez
Keyword(s):  
Low Flow ◽  
Effective Technique

DEVELOPMENT OF STREAMFLOW DROUGHT INDICES IN THE MORAVA RIVER BASIN

2020 ◽  
Author(s):  
Ondrej Ledvinka ◽  
◽  
Pavel Coufal ◽  
Keyword(s):  
Time Series ◽  
Kendall Test ◽  
Drought Indices ◽  
Drought Period ◽  
Left Hand ◽  
Low Flows ◽  
Current Period ◽  
Catchment Size ◽  
Morava River ◽  
The Stability

The territory of Czechia currently suffers from a long-lasting drought period which has been a subject of many studies, including the hydrological ones. Previous works indicated that the basin of the Morava River, a left-hand tributary of the Danube, is very prone to the occurrence of dry spells. It also applies to the development of various hydrological time series that often show decreases in the amount of available water. The purpose of this contribution is to extend the results of studies performed earlier and, using the most updated daily time series of discharge, to look at the situation of the so-called streamflow drought within the basin. 46 water-gauging stations representing the rivers of diverse catchment size were selected where no or a very weak anthropogenic influences are expected and the stability and sensitivity of profiles allow for the proper measurement of low flows. The selected series had to cover the most current period 1981-2018 but they could be much longer, which was considered beneficial for the next determination of the development direction. Various series of drought indices were derived from the original discharge series. Specifically, 7-, 15- and 30-day low flows together with deficit volumes and their durations were tested for trends using the modifications of the Mann– Kendall test that account for short-term and long-term persistence. In order to better reflect the drivers of streamflow drought, the indices were considered for summer and winter seasons separately as well. The places with the situation critical to the future water resources management were highlighted where substantial changes in river regime occur probably due to climate factors. Finally, the current drought episode that started in 2014 was put into a wider context, making use of the information obtained by the analyses.

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