Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Tuesday 7 July - 16:30-18:00 UNESCO Miollis - ROOM XVI

2212 (a) - Climate change and freshwater – 1: State of knowledge

Parallel Session

Lead Convener(s): C. Cudennec (IAHS, Allenvi, Agrocampus Ouest, Rennes, France), L. Longuevergne (CNRS, University Rennes 1, Rennes, France)

Convener(s): S. Demuth (UNESCO, Paris, France), P. Flammarion (Allenvi, IRSTEA, Paris, France), C. Caponi (WMO, Geneva, Switzerland)


Impacts of Climate Change on Freshwater Resources and Managing Global Risks

T. Oki (University of Tokyo, Tokyo, Japan)

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Impacts of Climate Change on Freshwater Resources and Managing Global Risks

T. Oki (1)
(1) University of Tokyo, Tokyo, Japan

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The real hydrological cycles on the Earth are not natural anymore. Humans are now driving changes in atmospheric processes through emission of green-house gases and land cover changes directly and indirectly. Global mean temperature is projected to rise approximately proportional to the cumulative total anthropogenic CO2 emissions from 1870 (AR5, IPCC WGI). Temperature rise itself will have direct impacts on the availability of water resources through changing flow regimes in snow-dominant or glacier-effluent river basins, and it will also be associated with sea level rise because thermal expansion is one of the major causes of observed and projected sea level rises. Further, climate change is projected to alter hydrological cycles: changing temporal and geographical patterns of hydrological components, such as precipitation, evapotranspiration, runoff, and ground water recharge, and particularly in their extremes. Consequently, the frequency of floods and/or droughts is projected to increase some parts of the world.

However, as articulated in the AR5 of IPCC WGII, “Risk of climate-related impacts results from the interaction of climate-related hazards (including hazardous events and trends) with the vulnerability and exposure of human and natural systems”, increasing frequency of natural hazards, such as torrential rainfall or long-lasting heat wave, alone will not cause damages on human and natural systems, and both climate and social changes are relevant for planning sustainable development in the future.

AR5 (WGII) also says “Significant co-benefits, synergies, and tradeoffs exist between mitigation and adaptation and among different adaptation responses; interactions occur both within and across regions”. Mitigation and/or adaptation actions should not be planned in an isolated manner, but should be integrated into wider frameworks, such as integrated water resources management and sustainable development. It would preferably be integrated into a risk management framework assessing and managing possible global risks, and ultimately pursue increasing human well-beings.


Hydrometeorological and hydroclimatic worldwide monitoring, data sharing, cooperation and services

B. Stewart (former Director, Croydon, Victoria, Australia), H. Lins (President of WMO Commission for Hydrology, Washington, United States of America)

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Hydrometeorological and hydroclimatic worldwide monitoring, data sharing, cooperation and services

B. Stewart (1) ; H. Lins (2)
(1) former Director, Department of climate and water, wmo, Croydon, Victoria, Australia; (2) President of WMO Commission for Hydrology, Washington, United States of America

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Freshwater resources are essential to all forms of life and, in a changing environment, hydrometeorological and hydroclimatic information are critical to ensure that resources are managed sustainably.  Our precious freshwater resources are under increasing stress due to a range of factors. These include, inter alia, growing populations, increasing food and industrial production and a changing and variable climate. Unless we improve the availability of, and access to, good quality hydrometeorological and hydroclimatic information, we will not be able to fully understand and manage our water resources in a sustainable manner and monitor the implications of future decisions.


In this regard, the current status of monitoring climatic change and its impacts, with an emphasis on global freshwater resources is reviewed.  In particular, the value of comprehensive hydrometeorological and hydroclimatic monitoring is described, including international efforts to facilitate and improve data collection and accessibility. Benefits from monitoring include improved understanding of the state and variability of freshwater resources, as well as reduced uncertainty in resource management decision-making under climatic change.  Additionally, the status of, and efforts associated with, the promotion of regional and international data sharing are described. The value associated with the combination of monitoring, data sharing and cooperation between relevant agencies are realized through the services that can be provided. Finally, the efforts of the hydrological community to provide hydrological services, the importance of a quality management framework for the collection and presentation of data, the development of associated information systems, data registries, and web services for data sharing are emphasized.


In order to manage our freshwater resources in a sustainable manner, we must learn from the mistakes of the past and support the collection of hydrometeorological and hydroclimatic data into future. This requires two actions:  1) reversing the current trend in declining monitoring stations and the data and information derived from them; and 2) improving the collection, processing, and presentation of these data through innovative new technologies.


Responding to the Challenges of Water Security: the Eighth Phase of the International Hydrological Programme 2014-2021

B. Jimenez-Cisneros (UNESCO, Paris, France)

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Responding to the Challenges of Water Security: the Eighth Phase of the International Hydrological Programme 2014-2021

B. Jimenez-Cisneros (1)
(1) UNESCO, IHP, Paris, France

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This paper presents the major water challenges at global, regional and local level, including adaptation to climate change, based on the AR5 IPCC findings. It relates how the International Hydrological Programme (IHP) will respond in its VIIIth Phase to water-related risks and seize opportunities to contribute to water security at all levels. Cooperation between science and innovation and policy lie at the core of this strategy.


Management of natural resources must draw on science and innovation to be sustainable. From this perspective, the UNESCO-IHP Member States periodically define priorities for research, technological development, innovation and education. To implement the priorities in a coordinated manner, Member States works with the IHP Secretariat based at UNESCO HQ, as well as the UNESCO “Water Family”, consisting of UNESCO-IHE, a Category I Centre located in the Netherlands; the World Water Assessment Programme, based in Italy, which produces the UN World Water Development Report; thirty Category II Centres under the auspices of UNESCO; and thirty-five water Chairs around the globe.


IHP’s role in this context is to put in place procedures for the use of knowledge and innovation to adapt to climate changes impacts in the water sector, and to increase resilience to water-related disasters.


River flood risk and climate change

Z. Kundzewicz (Institute for Agricultural and Forest Environment, Polish Academy of Sciences, Poznan, Poland)

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River flood risk and climate change

Z. Kundzewicz (1)
(1) Institute for Agricultural and Forest Environment, Polish Academy of Sciences, Department of Climate and Water Resources, Poznan, Poland

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River floods are an important problem area related to freshwater resources, at any spatial scale – from local to global. More than 10% of the global population are currently living in flood-prone areas and about 1% of the global population are, on average, exposed to floods each year. Average global flood damage reaches tens of billions of US$ and the number of fatalities amounts to thousands. Flood losses are higher in developed countries, while relative fatality rates and economic losses expressed as a proportion of GDP are higher in developing countries.


Observations of changes in climate, hydrological / terrestrial, and socio-economic systems influencing flood risk are examined. Despite the diagnosed extreme-precipitation based signal, and its possible link to changes in flood patterns, no gauge-based evidence had been found for a climate-driven, globally widespread change in the magnitude/frequency of floods during the last decades. There are strong regional and sub-regional variations in the trends. Moreover, it has not been generally possible to attribute rain-generated peak streamflow trends to anthropogenic climate change. Indeed, economic losses from floods have greatly increased, but this has been primarily attributed to increasing exposure and damage potential and not to climate change.


Further, model-based projections for the future are critically discussed. Projected changes from both global and regional studies indicate that it is likely that the frequency and intensity of heavy precipitation, or the proportion of total rainfall from heavy falls, will increase. Physical reasoning suggests that projected increases in intense rainfall would contribute to increases in precipitation-generated flooding, while less snowmelt flooding and earlier spring peak flows in snowmelt-fed rivers are expected in the warmer climate. Increase of flood hazard is projected over many areas.


Studies that project future flood losses and casualties indicate that, when no adaptation is undertaken, future anthropogenic climate change is likely to lead to increasing flood losses, alongside the increase in exposure linked to ongoing economic development, and the total increase would depend on the degree of warming.


Finally, uncertainty in our understanding of past floods and projections for the future is reviewed, with identification of gaps in knowledge. The impacts of climate change on flood characteristics are highly sensitive to the detailed nature of those changes and presently we have only low confidence in numerical projections of changes in flood magnitude or frequency resulting from climate change. Attention is drawn to the fact that over less than a decade, projections of flood hazard in Europe have dramatically changed. This is of vast practical relevance, hence interpretation of such changes has to be sought, related to both different climate scenarios and different modeling approaches.


Adaptation to changing water demand and climates in Sub-Saharan Africa: the role of groundwater

R. Taylor (University College London, London, United Kingdom)

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Adaptation to changing water demand and climates in Sub-Saharan Africa: the role of groundwater

R. Taylor (1)
(1) University College London, Geography, London, United Kingdom

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Freshwater demand in Sub-Saharan Africa (SSA) is expected to increase substantially in coming decades with projected rises in land under irrigation and water volumes required for domestic and industrial purposes.  Anthropogenic warming is projected to further amplify variability in rainfall and river discharge that is already the most extreme in the world. Current metrics of freshwater availability (e.g. water stress index, relative water demand) misrepresent the “water crisis” in SSA as they greatly exaggerate freshwater demand, define renewable freshwater resources in terms of mean river discharge and, critically, exclude groundwater storage. Total groundwater storage in Africa (~0.66 million km3) is more than 100 times annual renewable freshwater resources, and more than 20 times the volume of freshwater stored in African lakes. Although substantial quantities of fossil groundwater in Africa have long been known to exist and are heavily exploited in arid landscapes remote from people (e.g. Great Man-Made River Project), less well understood is the comparatively small (equivalent to water depth of 0.5m) but vital groundwater storage that underlies much of SSA where people live.  The extent to which this estimated groundwater storage is both accessible and renewable remains unclear. Recent research based on ground-based observations in semi-arid and humid areas of Tanzania and Uganda reveals the strong dependence of groundwater recharge on heavy rainfall events (>10 mm per day) and extreme rain events associated with the El Niño Southern Oscillation (ENSO). Consequently, the shift to fewer but heavier rainfall events projected under climate change may enhance groundwater recharge while reducing rain-fed soil moisture and exacerbating flooding. Under such circumstances, increased use of groundwater resources not only to supplement soil moisture through irrigation but also to meet increased freshwater demand may prove a hydro-logical adaptation in SSA.  Increased reliance upon groundwater resources has led to groundwater depletion of regional aquifer systems in the USA, China and India through competitive abstraction and aquifer mismanagement.  In contrast, aquifer systems underlying much of SSA are localized and characterized by low transmissivities and low storage. ‘Small is beautiful’ since these systems greatly restrict the impact of competitive, unregulated abstraction witnessed in other groundwater-dependent countries and enable low-intensity abstraction for which the impacts of overuse are largely localized. Thus, the prevailing geology naturally resolves the ‘Tragedy of the Commons’ that complicates management of productive, regional aquifer systems. Indeed, the potential for distributed, low-intensity groundwater use strongly complements land tenure systems in SSA that are characterized by a large number of distributed, smallholder (< 1 hectare) plots. Groundwater in SSA therefore represents a low-cost, distributed and potentially renewable store of freshwater that can enable many communities to adapt to changing water demand and climates. Two key physical challenges that currently constrain the realization of this potential are: (1) reducing the prohibitively high cost of drilling that currently impedes the development of groundwater by small landholders; and (2) resolving the aggregated impact of multiple low-intensity groundwater users to ensure the continuity of groundwater supplies and groundwater-dependent ecosystems. 


Groundwater on North Sea islands in a future climate – a geophysical approach

H. Wiederhold (Leibniz Institute for Applied Geophysics, Hannover, Germany)

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Groundwater on North Sea islands in a future climate – a geophysical approach

H. Wiederhold (1)
(1) Leibniz Institute for Applied Geophysics, Hannover, Germany

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For the North Sea Region climate change scenarios predict a shift of precipitation to the winter season leading to an enhanced groundwater recharge and rising water table. Additionally a sea level rise is expected leading to a new balance of freshwater and groundwater in the subsurface with consequences for, e.g., water supply, wetland drainage, construction stability. In the EU Interreg project CLIWAT (climate and water) the consequences of climate change to the groundwater systems were investigated in seven project areas in Denmark, Germany, the Netherlands and Belgium (CLIWAT Working Group 2011, Hinsby et al. 2012). Here the approach is shown exemplarily for the German North Sea island Borkum (Sulzbacher et al. 2012, Wiederhold et al. 2013).

The main challenge in the study of coastal aquifers in Northern Germany is the freshwater/saltwater environment. The water supply of the North Sea offshore islands is in many cases restricted to a freshwater lens and intrusion of seawater is a major constraint on groundwater utilization. To study the impact of climate change on the freshwater lens of a barrier island, a density-dependent groundwater model was developed. The structure and parameters of this model were designed using information from boreholes and various geophysical and hydrogeological investigations. To characterize the hydrogeophysical setting of a freshwater/saltwater system, we need a description of the actual situation including temporal changes in the freshwater/saltwater transition zone. This concerns the study of water salinity and its changes. Due to the strong contrast in electrical conductivity between seawater and freshwater, resistivity and electromagnetic methods are most suitable to map salinity in the subsurface. To overcome ambiguity in interpretation, the combination with methods such as nuclear magnetic resonance or seismics turned out to be successful.

This data were used to generate a hydraulic model for density-dependent groundwater modelling that is able to predict the long-term behaviour of the system under changing climatic conditions. To monitor the temporal behaviour, permanent resistivity installations are a cost-efficient alternative to repetitive soundings. The data acquired in periods of years or decades can help to improve the groundwater model and its implications.

CLIWAT WORKING GROUP (2011): Groundwater in a Future Climate - The CLIWAT Handbook. ISBN: 87-7788-265-2, Central Denmark Region, Aarhus. http://cliwat.eu/xpdf/groundwater_in_a_future_climate.pdf

Hinsby, K., Auken, E., Oude Essink, G. H. P., de Louw, P., Jørgensen, F., Siemon, B., Sonnenborg, T. O., Vandenbohede, A., Wiederhold, H., Guadagnini, A. & Carrera, J. (Eds.) (2012): Assessing the impact of climate change for adaptive water management in coastal regions. Hydrol. Earth Syst. Sci., 17. http://www.hydrol-earth-syst-sci.net/special_issue149.html.

Sulzbacher, H., Wiederhold, H., Siemon, B., Grinat, M., Igel, J., Burschil, T., Günther, T. & Hinsby, K. (2012): Numerical modelling of climate change impacts on freshwater lenses on the North Sea Island of Borkum using hydrological and geophysical methods. Hydrol. Earth Syst. Sci., 16, 3621–3643, doi:10.5194/hess-16-3621-2012.

Wiederhold, H., Sulzbacher, H., Grinat, M., Günther, T., Igel, J., Burschil, T. & Siemon, B. (2013): Hydrogeophysical characterization of freshwater/saltwater systems – case study: Borkum Island, Germany. First Break, 31, 109-117.