scholarly journals Investigation of the long-term variations in hydro-climatology of the Dinder and Rahad basins and its implications on ecosystems of the Dinder National Park, Sudan

2016 ◽  
Author(s):  
Khalid Hassaballah ◽  
Yasir Mohamed ◽  
Stefan Uhlenbrook
Keyword(s):  
National Park ◽  
River Flow ◽  
Statistical Tests ◽  
Climatic Variability ◽  
Rate Of Change ◽  
Low Flow ◽  
Mk Test ◽  
Increasing Trend ◽  
Long Term Variations

Abstract. Hydro-climatic variability plays a pivotal role in structuring the biophysical environment of riverine and floodplain ecosystems. Variability is natural, but can also be enhanced by anthropogenic interventions. Alterations of hydro-climatic variables can have significant impacts on the ecohydrological functions of rivers and related ecosystems. Loss of biodiversity and degradation of ecosystems have caused increasing concern about the current situation of the Dinder and Rahad River basins (D&R), particularly the ecosystems of the Dinder National Park (DNP). However the causes are not yet fully understood. Conservation of the DNP ecosystems for direct and indirect human benefit is one of major challenges facing the country. This paper examines the long-term variations of streamflow, rainfall and temperature over the D&R and its implications on DNP ecosystems. Statistical tests of Mann–Kendall (MK) and Pettitt were used. The analysis was carried out for twelve precipitation, one temperature, and two streamflow gauging stations over different time periods. Streamflow characteristics of magnitude, duration, timing, frequency and rate of change in flow that likely impact the ecological functions of the ecosystem of the DNP, were analysed using the Indicators of Hydrologic Alterations (IHA). The MK test showed statistically significant increasing trends of temperature. The mean annual and monthly mean precipitation showed no significant change. Streamflow of the Rahad River showed a significant increasing trend in annual and monthly means at Al-Hawata station, while no significant trend in Dinder River flows at Al-Gewisi station could be observed. However, the Dinder river showed significant decreasing trend in maximum annual and monthly mean and maximum flow during August (month of high flow), and increasing trend during November (month of low flow). The IHA analysis indicated that the Rahad River flow was coupled with significant upward alterations in some of the hydrological indicators. In contrast, the Dinder River flow was coupled with significant downward alterations. This alterations in Dinder river flow are likely affect the ecosystems in DNP negatively. Alterations in magnitude and duration of the annual flood peaks that reduce the amount of water flowing to the river-floodplain, may diminish the production of native flora and fauna, and animal migration that may be linked to floodplain inundation.

scholarly journals Calibration of hydrological models for ecologically relevant streamflow predictions: a trade-off between fitting well to data and estimating consistent parameter sets?

2020 ◽  
Vol 24 (3) ◽  
pp. 1031-1054 ◽  
Author(s):  
Thibault Hallouin ◽  
Michael Bruen ◽  
Fiachra E. O'Loughlin
Keyword(s):  
Flow Regime ◽  
River Flow ◽  
Freshwater Ecosystems ◽  
Living Environment ◽  
Rate Of Change ◽  
Low Flow ◽  
Hydrological Models ◽  
Flow Conditions ◽  
Local Flow ◽  
Trade Off

Abstract. The ecological integrity of freshwater ecosystems is intimately linked to natural fluctuations in the river flow regime. In catchments with little human-induced alterations of the flow regime (e.g. abstractions and regulations), existing hydrological models can be used to predict changes in the local flow regime to assess any changes in its rivers' living environment for endemic species. However, hydrological models are traditionally calibrated to give a good general fit to observed hydrographs, e.g. using criteria such as the Nash–Sutcliffe efficiency (NSE) or the Kling–Gupta efficiency (KGE). Much ecological research has shown that aquatic species respond to a range of specific characteristics of the hydrograph, including magnitude, frequency, duration, timing, and the rate of change of flow events. This study investigates the performance of specially developed and tailored criteria formed from combinations of those specific streamflow characteristics (SFCs) found to be ecologically relevant in previous ecohydrological studies. These are compared with the more traditional Kling–Gupta criterion for 33 Irish catchments. A split-sample test with a rolling window is applied to reduce the influence on the conclusions of differences between the calibration and evaluation periods. These tailored criteria are shown to be marginally better suited to predicting the targeted streamflow characteristics; however, traditional criteria are more robust and produce more consistent behavioural parameter sets, suggesting a trade-off between model performance and model parameter consistency when predicting specific streamflow characteristics. Analysis of the fitting to each of 165 streamflow characteristics revealed a general lack of versatility for criteria with a strong focus on low-flow conditions, especially in predicting high-flow conditions. On the other hand, the Kling–Gupta efficiency applied to the square root of flow values performs as well as two sets of tailored criteria across the 165 streamflow characteristics. These findings suggest that traditional composite criteria such as the Kling–Gupta efficiency may still be preferable over tailored criteria for the prediction of streamflow characteristics, when robustness and consistency are important.

scholarly journals Long term prediction of flood occurrence

2016 ◽  
Vol 373 ◽  
pp. 189-192 ◽  
Author(s):  
Cristina Aguilar ◽  
Alberto Montanari ◽  
María José Polo
Keyword(s):  
Flow Regime ◽  
River Flow ◽  
Research Question ◽  
Flood Frequency ◽  
High Flow ◽  
Low Flow ◽  
Physical Explanation ◽  
Po River ◽  
Flood Season

Abstract. How long a river remembers its past is still an open question. Perturbations occurring in large catchments may impact the flow regime for several weeks and months, therefore providing a physical explanation for the occasional tendency of floods to occur in clusters. The research question explored in this paper may be stated as follows: can higher than usual river discharges in the low flow season be associated to a higher probability of floods in the subsequent high flow season? The physical explanation for such association may be related to the presence of higher soil moisture storage at the beginning of the high flow season, which may induce lower infiltration rates and therefore higher river runoff. Another possible explanation is persistence of climate, due to presence of long-term properties in atmospheric circulation. We focus on the Po River at Pontelagoscuro, whose catchment area amounts to 71 000 km2. We look at the stochastic connection between average river flows in the pre-flood season and the peak flows in the flood season by using a bivariate probability distribution. We found that the shape of the flood frequency distribution is significantly impacted by the river flow regime in the low flow season. The proposed technique, which can be classified as a data assimilation approach, may allow one to reduce the uncertainty associated to the estimation of the flood probability.

scholarly journals Many-year Fluctuations of River Runoff in South-taiga Subzone of the Western Siberia

2013 ◽  
pp. 34-45
Author(s):  
Keyword(s):  
Western Siberia ◽  
River Flow ◽  
Atmospheric Precipitation ◽  
Southern Taiga ◽  
Low Flow ◽  
Groundwater Levels ◽  
Level Regime ◽  
Southern Taiga Subzone ◽  
Bog Water

A detailed analysis of river flow long-term changes in the Southern taiga subzone of Western Siberia has been carried out with the Chaya River basin as an example. Causal statistical analysis of changes in groundwater levels, bog water level, air temperature and atmospheric precipitation has been performed. The conducted studies revealed a statistically significant trend in the increase of surface runoff in the winter low flow of the Chaya River and its large tributaries (the Iksa and the Parbig), as well as the underground runoff component for virtually the entire year. An ambiguous regularity has been observed in the change of the level regime of rivers. The main reason for the observed changes in the water regime of the said territory is the redistribution of atmospheric moisture and shifting of the boundaries of hydrological seasons.

scholarly journals ASSESSMENT OF LONG TERM CLIMATIC VARIABILITY OF UTTARAKHAND

2018 ◽  
Vol 1 (4) ◽  
Author(s):  
Sujeet Kumar ◽  
Shakti Suryavanshi
Keyword(s):  
Minimum Temperature ◽  
Monsoon Season ◽  
Climatic Variability ◽  
Kendall Test ◽  
Summer Season ◽  
Climatic Variables ◽  
Maximum Temperature ◽  
Mountain Areas ◽  
Mk Test ◽  
Increasing Trend

A trend analysis was performed for historic (1901-2002) climatic variables (Rainfall, Maximum Temperature and Minimum Temperature) of Uttarakhand State located in Northern India. In the serially independent climatic variables, Mann-Kendall test (MK test) was applied to the original sample data. However, in the serially correlated series, prewhitening is utilized before employing the MK test. The results of this study indicated a declining trend of rainfall in monsoon season for seven out of thirteen districts of Uttarakhand state. However, an increasing trend was observed in Haridwar and Udhamsingh Nagar districts for summer season rainfall. For maximum and minimum temperature, a few districts exhibited a declining trend in monsoon season whereas many districts exhibited an increasing trend in winter and summer season. Mountain dominated areas (as Uttarakhand state) are specific ecosystems, distinguished by their diversity, sensitivity and intricacy. Thus the variability of rainfall and temperature has a severe and rapid impact on mountainous ecosystems. Nevertheless, mountains have significant impacts on hydrology, which may further threaten populations living in the mountain areas as well as in adjacent, lowland regions.

Fresh water inflows to the Firth of Clyde

1986 ◽  
Vol 90 ◽  
pp. 55-66
Author(s):  
T. Poodle
Keyword(s):  
Seasonal Variation ◽  
Fresh Water ◽  
River Flow ◽  
Low Flow ◽  
Flow Data ◽  
Fresh Water Input ◽  
Flow Frequency

SynopsisRainfall and river flow data have been used to calculate the fresh water input to the Firth of Clyde at key locations. The importance of seasonal variation and the recurrence of period of low flow is illustrated. Long term flow frequency is also analysed and related to recent events.

Long term changes in the functioning of a karst aquifer under anthropogenic forcing

2021 ◽  
Author(s):  
Cousquer Yohann ◽  
Jourde Hervé
Keyword(s):  
Surface Water ◽  
Flow Rate ◽  
Climatic Variability ◽  
Karst Aquifer ◽  
Active Management ◽  
Low Flow ◽  
Spring Discharge ◽  
Long Term Changes ◽  
And Storage

<p>A quantitative estimation of the sustainability of groundwater resources is a challenge for water supplies. This study focuses on karstic hydro systems, which provide water resources to a large part of the Mediterranean population. Here, we address the long-term changes in the functioning of the Lez karst aquifer, which has been providing water to the city of Montpellier since the XIX<sup>th</sup> century.  Before 1965, only the natural overflow of the spring was used, then pumping in the spring, down to -6.50 m below the overflow level of the spring, was performed until 1981. After this date, the management of the water resource consisted in pumping groundwater at a much greater flow rate (up to 2000 l/s) than the natural discharge during low flow (200 l/s), which seasonally generates important drawdowns (down to ~25 m) at regional scale.</p><p>The available time series consist in more than 70 years of discharge and water table (with some gaps) that encompass the three kinds of groundwater management, spanning from a passive management to the current active management. The change in water budget terms over time (before and after active management) highlights the modification of transfers and storage in the different karst compartments (epikarst, unsaturated zone, saturated zone), and the climatic variability of precipitation, evapotranspiration at inter-annual. A lumped parameter model was set up in order to simulate spring discharge, while accounting for surface water and grandwater level dynamics, and better assess the changes in the storage dynamics within the different compartments (matrix-conduits) of the karst. A robust parameter estimation, accounting for groundwater discharge and surface water discharge observations, has been conducted using a Monte-Carlo procedure. In order to obtaines a robust model, divers data type such as groundwater flow, surface flow and water level, have been used. [H1]  Once the model was calibrated over (1955-2020) reference period, several prospective management scenarios based on pumping discharge were simulated with an estimation of predictive uncertainty. This allowed evaluating the influence of pumping at large flow rate (active management) on the flux and storage on matrix-conduits exchanges of such karst hydrosystem. A modification on both the discharge rates and the direction of water exchanges between compartments, and especially between matrix and conduits, have been noted. The importance of climatic variability at inter-annual scale on water availability has been discussed as well.</p>

A large-scale hydroclimatological perspective on western European river flow regimes

2012 ◽  
Vol 44 (5) ◽  
pp. 809-833 ◽  
Author(s):  
Donna Wilson ◽  
David M. Hannah ◽  
Glenn R. McGregor
Keyword(s):  
Large Scale ◽  
Western Europe ◽  
River Flow ◽  
Flow Regimes ◽  
Climatic Conditions ◽  
Low Flow ◽  
Annual Rainfall ◽  
Time Variability ◽  
Runoff Generation

A novel flow regime classification scheme was applied to 141 river basins across western Europe, providing more robust analysis of space–time variability in regimes and their driving hydroclimatological processes. Regime shape (timing) and magnitude (size) were classified to regionalise long-term average flow regimes and to quantify year-to-year variation in regimes for each basin. Six long-term regime shape regions identified differences in seasonality related to latitude and altitude. Five long-term magnitude regions were linked to location plus average annual rainfall. Spatial distribution of long-term regimes reflected dominant climate and runoff generation processes. Regions were used to structure analysis of (relative) inter-annual regime dynamics. Six shape and five magnitude inter-annual regimes were identified; and regime stability (switching) assessed at pan-European, regional and basin scales. In some years, certain regime types were more prevalent, but never totally dominant. Regime shape was more stable at higher altitude due to buffering by frozen water storage-release (cf. more variable rainfall-runoff at lower altitudes). The lower inter-annual magnitude regimes persisted across larger domains (cf. higher magnitude) due to the more widespread climatic conditions generating low flow. Notably, there was limited spatio-temporal correspondence between regime shape and magnitude, suggesting variations in one attribute cannot be used to infer the other.

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