The role of storage capacity in coping with intra- and inter-annual water variability in large river basins

Abstract

Societies and economies are challenged by variable water supplies. Water storage infrastructure, on a range of scales, can help to mitigate hydrological variability. This study uses a water balance model to investigate how storage capacity can improve water security in the world's 403 most important river basins, by substituting water from wet months to dry months. We construct a new water balance model for 676 'basin-country units' (BCUs), which simulates runoff, water use (from surface and groundwater), evaporation and trans-boundary discharges. When hydrological variability and net withdrawals are taken into account, along with existing storage capacity, we find risks of water shortages in the Indian subcontinent, Northern China, Spain, the West of the US, Australia and several basins in Africa. Dividing basins into BCUs enabled assessment of upstream dependency in transboundary rivers. Including Environmental Water Requirements into the model, we find that in many basins in India, Northern China, South Africa, the US West Coast, the East of Brazil, Spain and in the Murray basin in Australia human water demand leads to over-abstraction of water resources important to the ecosystem. Then, a Sequent Peak Analysis is conducted to estimate how much storage would be needed to satisfy human water demand whilst not jeopardizing environmental flows. The results are consistent with the water balance model in that basins in India, Northern China, Western Australia, Spain, the US West Coast and several basins in Africa would need more storage to mitigate water supply variability and to meet water demand.

Focus on water storage for managing climate extremes and change

“…This global analysis underscores the importance of long time series for developing more reliable data on reservoir yields; however, future climate change may alter the characteristics of these flow systems. A global water balance model was used to assess the value of storage capacity for enhancing water security in the world's∼400 largest river basins by storing water from wet months for use during dry months (Gaupp et al 2015). This analysis identified water shortage risks in India, N China, Spain, W US, Australia, and many parts of Africa.…”

Safeguarding water availability for food and ecosystems under global change : modelling and assessment of the role of environmental flows

“…Additionally, all the global methods were validated using local EFRs assessments based on ecological and hydrological measurements. The newly developed VMF method was the best fitted method for global use and was implemented in chapters 3, 4 and 5 of this thesis and in other global water and environmental assessments , Gaupp, Hall et al 2015. In Chapter 3, the aim of the study was to identify where, when and why EFRs were not satisfied globally (Figure 6.2).…”

“…For example, our results show that part of potentially affected irrigation extractions might be affected by implementing EFRs especially in modified intermittent rivers and that specific flow releases from storage could be applied to preserve ecosystems (Gaupp, Hall et al 2015). Therefore, when river basin communities decide to implement EFRs, trade-offs between water users should be discussed.…”

“…For example, Mediterranean areas are very subjective to both natural and anthropogenic deficits due to long dry seasons combined with high irrigation extractions. Therefore, to tackle anthropogenic deficit, it might be necessary to increase water storage (Gaupp, Hall et al 2015) and decrease the production of water intensive crops in water scarce areas (Wichelns 2001, Aldaya, Martínez-Santos et al 2010. The level of intervention to decrease deficit should depends on flow thresholds above which water extractions would lead to ecosystem collapse.…”

“…A couple of recent global assessments used the newly improved Variable Monthly Method (VMF) ) which uses refined temporal scale with previously validated local study cases , Gaupp, Hall et al 2015, Grill, Lehner et al 2015, Sadoff 2015. To maintain rivers in a healthy state, it was shown that EFRs should represent between 20 and 50% of mean annual flow (Smakhtin, Revenga et al 2004.…”