Impact of climate change on the hydrological regime of the Indus, Ganges and Brahmaputra river basins: a review of the literature

Nepal, Santosh; Shrestha, A. B.

doi:10.1080/07900627.2015.1030494

Cited by 141 publications

(72 citation statements)

References 50 publications

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“…Therefore, the changes in river flow are likely to be mainly driven by precipitation on the annual scale which more than counters the evaporation caused by increasing temperatures in the model. This is consistent with other analyses of precipitation that also use the A1B climate scenario (Nepal and Shrestha, 2015), which is a useful result. The trajectories of the annual average river flow, evaporation and precipitation for the Indus are much flatter, showing little or no trend.…”

Section: Discussionsupporting

confidence: 91%

“…The RCMs are also able to reproduce the inter-annual variability of the region although they underestimate the magnitude of the variation . The GCMs in the AR4 ensemble tend to exhibit cold and wet biases compared to observations both globally (Nohara et al, 2006) and for South Asia . Although these are generally reduced in the RCM simulations there is a cold bias in the RCM that is probably carried over from the larger bias in the GCMs Kumar et al, 2013).…”

Section: Comparison Of Present-day Driving Data With Observationsmentioning

confidence: 98%

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South Asia river-flow projections and their implications for water resources

Mathison

Wiltshire

Falloon

et al. 2015

Hydrol. Earth Syst. Sci.

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Abstract. South Asia is a region with a large and rising population, a high dependence on water intense industries, such as agriculture and a highly variable climate. In recent years, fears over the changing Asian summer monsoon (ASM) and rapidly retreating glaciers together with increasing demands for water resources have caused concern over the reliability of water resources and the potential impact on intensely irrigated crops in this region. Despite these concerns, there is a lack of climate simulations with a high enough resolution to capture the complex orography, and water resource analysis is limited by a lack of observations of the water cycle for the region. In this paper we present the first 25 km resolution regional climate projections of river flow for the South Asia region. Two global climate models (GCMs), which represent the ASM reasonably well are downscaled (1960-2100) using a regional climate model (RCM). In the absence of robust observations, ERA-Interim reanalysis is also downscaled providing a constrained estimate of the water balance for the region for comparison against the GCMs (1990GCMs ( -2006. The RCM river flow is routed using a river-routing model to allow analysis of present-day and future river flows through comparison with available river gauge observations. We examine how useful these simulations are for understanding potential changes in water resources for the South Asia region. In general the downscaled GCMs capture the seasonality of the river flows but overestimate the maximum river flows compared to the observations probably due to a positive rainfall bias and a lack of abstraction in the model. The simulations suggest an increasing trend in annual mean river flows for some of the river gauges in this analysis, in some cases almost doubling by the end of the century. The future maximum river-flow rates still occur during the ASM period, with a magnitude in some cases, greater than the present-day natural variability. Increases in river flow could mean additional water resources for irrigation, the largest usage of water in this region, but has implications in terms of inundation risk. These projected increases could be more than countered by changes in demand due to depleted groundwater, increases in domestic use or expansion of water intense industries. Including missing hydrological processes in the model would make these projections more robust but could also change the sign of the projections.

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Section: Discussionsupporting

confidence: 91%

Section: Comparison Of Present-day Driving Data With Observationsmentioning

confidence: 98%

South Asia river-flow projections and their implications for water resources

Mathison

Wiltshire

Falloon

et al. 2015

Hydrol. Earth Syst. Sci.

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“…The monsoon is the dominant contributor to the Brahmaputra discharge apart from glacier melt water (Immerzeel 2008). Past climate conditions in the region show an increasing trend in temperature of 0.6°C during the last century (Immerzeel 2008), while studies on precipitation are still inconclusive (Nepal and Shrestha 2015;Ray et al 2015). No long-term trend in discharge is apparent, only a slight increase in mean discharge of the last few decades (Sarker et al 2014;Ray et al 2015).…”

Section: Site Descriptionmentioning

confidence: 99%

“…For the end of the century (2075-2100), projected increases in air temperatures within the basin range from 2.3°C (Immerzeel 2008) to 4.8°C (Darby et al 2015;Masood et al 2015; Table 1B) relative to their respective reference periods within the years 1960 to 2000. Reported projections of future discharges of the Brahmaputra River span a wide range, in part because even current conditions are uncertain (Nepal and Shrestha 2015). Lutz et al (2014) estimated increases with 1-13 % by the mid-twenty-first century compared to 1998-2007, arguing that the loss of glacier area would be compensated by increases in melt rates.…”

Section: Synthesis Of Reported Parameter Values: Future Statementioning

confidence: 99%

Present to future sediment transport of the Brahmaputra River: reducing uncertainty in predictions and management

et al. 2016

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The Brahmaputra River in South Asia carries one of the world's highest sediment loads, and the sediment transport dynamics strongly affect the region's ecology and agriculture. However, present understanding of sediment conditions and dynamics is hindered by limited access to hydrological and geomorphological data, which impacts predictive models needed in management. We here synthesize reported peer-reviewed data relevant to sediment transport and perform a sensitivity analysis to identify sensitive and uncertain parameters, using the one-dimensional model HEC-RAS, considering both present and future climatic conditions. Results showed that there is considerable uncertainty in openly available estimates (260-720 Mt yr -1 ) of the annual sediment load for the Brahmaputra River at its downstream Bahadurabad gauging station (Bangladesh). This may aggravate scientific impact studies of planned power plant and reservoir construction in the region, as well as more general effects of ongoing land use change and climate change. We found that data scarcity on sediment grain size distribution, water discharge, and Manning's roughness coefficient had the strongest controls on the modelled sediment load. However, despite uncertainty in absolute loads, we showed that predicted relative changes, including a future increase in sediment load by about 40 % at Bahadurabad by 2075-2100, were consistent across multiple model simulations. Nevertheless, for the future scenarios we found that parameter uncertainty almost doubled for water discharge and river geometry, highlighting that improved information on these parameters could greatly advance the abilities to predict and manage current and future sediment dynamics in the Brahmaputra river basin.

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“…Hydrological projections based on different approaches indicate likely increases in flow at least during the first half of the 21 st century for particular subbasins [37,38] and at the basin scale [3,44,45,48]. Projections of changes in hydrological extremes in the UIB are very limited [49], but are at the same time very much desired [3,38,50]. …”

Section: Introductionmentioning

confidence: 99%

Climate Change Impacts on the Upper Indus Hydrology: Sources, Shifts and Extremes

et al. 2016

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The Indus basin heavily depends on its upstream mountainous part for the downstream supply of water while downstream demands are high. Since downstream demands will likely continue to increase, accurate hydrological projections for the future supply are important. We use an ensemble of statistically downscaled CMIP5 General Circulation Model outputs for RCP4.5 and RCP8.5 to force a cryospheric-hydrological model and generate transient hydrological projections for the entire 21st century for the upper Indus basin. Three methodological advances are introduced: (i) A new precipitation dataset that corrects for the underestimation of high-altitude precipitation is used. (ii) The model is calibrated using data on river runoff, snow cover and geodetic glacier mass balance. (iii) An advanced statistical downscaling technique is used that accounts for changes in precipitation extremes. The analysis of the results focuses on changes in sources of runoff, seasonality and hydrological extremes. We conclude that the future of the upper Indus basin’s water availability is highly uncertain in the long run, mainly due to the large spread in the future precipitation projections. Despite large uncertainties in the future climate and long-term water availability, basin-wide patterns and trends of seasonal shifts in water availability are consistent across climate change scenarios. Most prominent is the attenuation of the annual hydrograph and shift from summer peak flow towards the other seasons for most ensemble members. In addition there are distinct spatial patterns in the response that relate to monsoon influence and the importance of meltwater. Analysis of future hydrological extremes reveals that increases in intensity and frequency of extreme discharges are very likely for most of the upper Indus basin and most ensemble members.

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Impact of climate change on the hydrological regime of the Indus, Ganges and Brahmaputra river basins: a review of the literature

Cited by 141 publications

References 50 publications

South Asia river-flow projections and their implications for water resources

South Asia river-flow projections and their implications for water resources

Present to future sediment transport of the Brahmaputra River: reducing uncertainty in predictions and management

Climate Change Impacts on the Upper Indus Hydrology: Sources, Shifts and Extremes

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