Hydrological response of a dryland ephemeral river to southern African climatic variability during the last millennium

Benito, Gerardo; Thorndycraft, Varyl R.; Rico, María Teresa; Sánchez‐Moya, Y.; Sopeña, Alfonso; Botero, B. A.; Machado, María José; Davis, Michael; Pérez‐González, Alfredo

doi:10.1016/j.yqres.2011.01.004

Cited by 67 publications

(49 citation statements)

References 33 publications

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“…Various palaeoclimate studies in the winter rainfall zone of South Africa [20][21][22][23] have also contributed to the understanding of the long-term changes in climate in Namaqualand. Distinguishing local climate trends is essential as climate may not change uniformly across large areas.…”

Section: Introductionmentioning

confidence: 99%

Recent trends in the climate of Namaqualand, a megadiverse arid region of South Africa

Davis

Hoffman

Roberts³

2016

S. Afr. J. Sci.

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Namaqualand is especially vulnerable to future climate change impacts. Using a high-resolution (0.5°x0.5°) gridded data set (CRU TS 3.1) and individual weather station data, we demonstrated that temperatures as well as frequency of hot extremes have increased across this region. Specifically, minimum temperatures have increased by 1.4 °C and maximum temperatures by 1.1 °C over the last century. Of the five weather stations analysed, two showed evidence of a significant increase in the duration of warm spells of up to 5 days per decade and a reduction in the number of cool days (TX10P) by up to 3 days per decade. In terms of rainfall, we found no clear evidence for a significant change in annual totals or the frequency or intensity of rainfall events. Seasonal trends in rainfall did, however, demonstrate some spatial variability across the region. Spatial trends in evapotranspiration obtained from the 8-day MOD16 ET product were characterised by a steepening inland-coastal gradient where areas along the coastline showed a significant increase in evapotranspiration of up to 30 mm per decade, most notably in spring and summer. The increase in temperature linked with the increases in evapotranspiration pose significant challenges for water availability in the region, but further research into changes in coastal fog is required in order for a more reliable assessment to be made. Overall, the results presented in this study provide evidence-based information for the management of climate change impacts as well as the development of appropriate adaptation responses at a local scale.

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Section: Introductionmentioning

confidence: 99%

Recent trends in the climate of Namaqualand, a megadiverse arid region of South Africa

Davis

Hoffman

Roberts³

2016

S. Afr. J. Sci.

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“…The methodology applied was based on multi-source flood data including: (a) a two year continuous monitoring programme (2005)(2006)(2007)(2008), (b) hydrological rainfall-runoff modelling (1965 to 2006), (c) instrumental rainfall records (1870 to 2006), (d) documentary records since AD 1810, and (e) sedimentological records for the last 700 yr (Benito et al, 2011). The nested chronological approach provided by these overlapping periods enabled cross-checking and, in the case of the hydrological modelling, calibration allowing improved interpretation of the data.…”

Section: Methodsmentioning

confidence: 99%

“…The methodology and results of these palaeoflood records are discussed in Benito et al (2011). A set of probability distribution functions was fitted to the reconstructed flood data series and the parameters of these distribution functions were estimated by the maximum likelihood method (Stedinger and Cohn, 1986).…”

Section: Methodsmentioning

confidence: 99%

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Rainfall-runoff modelling and palaeoflood hydrology applied to reconstruct centennial scale records of flooding and aquifer recharge in ungauged ephemeral rivers

Benito

Botero

Thorndycraft

et al. 2011

Hydrol. Earth Syst. Sci.

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Abstract. In this study we propose a multi-source data approach for quantifying long-term flooding and aquifer recharge in ungauged ephemeral rivers. The methodology is applied to the Buffels River, at 9000 km 2 the largest ephemeral river in Namaqualand (NW South Africa), a region with scarce stream flow records limiting research investigating hydrological response to global change. Daily discharge and annual flood series were estimated from a distributed rainfall-runoff hydrological model (TETIS) using rainfall gauge records located within the catchment. The model was calibrated and validated with data collected during a two year monitoring programme (2005)(2006) at two stream flow stations, one each in the upper and lower reaches of the catchment. In addition to the modelled flow records, non-systematic flood data were reconstructed using both sedimentary and documentary evidence. The palaeoflood record identified at least 25 large floods during the last 700 yr; with the largest floods reaching a minimum discharge of 255 m 3 s −1 (450 yr return period) in the upper basin, and 510 m 3 s −1 (100 yr return period) in the lower catchment. Since AD 1925, the flood hydrology of the Buffels River has been characterised by a decrease in the magnitude and frequency of extreme floods, with palaeoflood discharges (period 1500-1921) five times greater than the largest modelled floods during the period 1965 -2006 Correspondence to: G. Benito (benito@ccma.csic.es) floods generated the highest hydrograph volumes, however their contribution to aquifer recharge is limited as this depends on other factors such as flood duration and storage capacity of the unsaturated zone prior to the flood. Floods having average return intervals of 5-10 yr (120-140 m 3 s −1 ) and flowing for 12 days are able to fully saturate the Spektakel aquifer in the lower Buffels River basin. Alluvial aquifer storage capacity limiting potential recharge by the largest floods is a common problem in arid environments, with the largest infiltration volumes favoured by increasing depth to groundwater levels.

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“…The hydrology of ephemeral rivers is dominated by occasional large flash floods that cause morphological fluvial changes (Tooth, 2000;Benito et al, 2011). Consequently, most geomorphological studies have been mainly concentrated on these greatest flow events, due to their impacts on the river channel changes, related river environments and human infrastructure (Greenbaum and Bergman, 2006;Grodek et al, 2012;Nardi and Rinaldi, 2015;Hooke, 2016b).…”

Section: Introductionmentioning

confidence: 99%

Topographical changes caused by moderate and small floods in a gravelly ephemeral river – 2D morphodynamic simulation approach

Lotsari

Calle

Benito

et al. 2017

Preprint

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Abstract. In ephemeral rivers, channel morphology represents a snapshot at the end of a succession of geomorphic changes performed by a flood. In most cases, the channel shape and bedform evolution during different phases of a flood hydrograph 15 are not recognized from field evidence. This paper analyzes the capabilities of morphodynamic modelling (Delft 2D) for resolving the evolution of a gravelly ephemeral river channel during consecutive, moderate-and low-magnitude discharge events. We pursue for schematic concepts for simulations in ephemeral gravely rivers that provide an outcome with the closest similarity to the post-flood reality. Based on the simulations, we analyze the morphodynamic evolution of Rambla de la Viuda The spatially varying grain size data and transport equations were the most important factors, in addition to the quality of recorded discharge, for the simulation results of the channel evolution. The total load equation worked better, compared to the 25 deterministic equation. The erosion and deposition can be in total greater during the long-lasting receding phase than during the rising phase. The deposition and erosion peaks are predicted to occur at the beginning of the moderate-magnitude discharge event, whereas deposition dominates throughout the event. On the contrary, the low-magnitude discharge event only experiences the peak of channel changes after the discharge peak. These different predicted erosion/deposition patterns suggest a hysteresis effect on the morphodynamic changes, and stress the importance of previous flood history (timing, succession and 30 magnitude) in understanding the geomorphic response of gravelly ephemeral rivers.Earth Surf. Dynam. Discuss., https://doi

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Hydrological response of a dryland ephemeral river to southern African climatic variability during the last millennium

Cited by 67 publications

References 33 publications

Recent trends in the climate of Namaqualand, a megadiverse arid region of South Africa

Recent trends in the climate of Namaqualand, a megadiverse arid region of South Africa

Rainfall-runoff modelling and palaeoflood hydrology applied to reconstruct centennial scale records of flooding and aquifer recharge in ungauged ephemeral rivers

Topographical changes caused by moderate and small floods in a gravelly ephemeral river – 2D morphodynamic simulation approach

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