Edited by Yan Huang and Siegfried Demuth
United Nations Education, Scientific and Cultural Organisation International Hydrological Programme VII
Flow Regimes from International Experimental and Network Data (FRIEND) Koblenz, 2010
HWRP – Hydrology and Water Resource Programme of WMO BfG – Federal Institute of Hydrology, Koblenz
German National Committee for the
International Hydrological Programme (IHP) of UNESCO and the Hydrology and Water Resources Programme (HWRP) of WMO Koblenz 2010
© IHP/HWRP Secretariat Federal Institute of Hydrology Am Mainzer Tor 1
56068 Koblenz • Germany Telefon: +49 (0) 261/1306-5435 Telefax: +49 (0) 261/1306-5422 http://ihp.bafg.de
International Hydrological Programme United Nations
Educational, Scientific and Cultural Organization
The report is a contribution towards the 6th FRIEND World Conference “Global Change: Facing Risks
and Threats to Water Resources”, which takes place in Fez, Morocco, 25 to 29 October 2010. This conference brings together the FRIEND community to discuss the impacts of global change in altering the hydrological cycle in different parts of the world. The outputs of this conference will provide guidance on how to mitigate and adapt to the new risks, threats and opportunities posed to water security by global change.
In 2010, UNESCO’s IHP FRIEND programme marks its 25th anniversary. It is one of the most successful IHP programmes of UNESCO. From a relatively modest beginning in 1985 with scientists from 7 European countries, FRIEND expanded to 162 countries in 2010 and has thus become a global programme not only with respect to its geographical coverage but also due to is vast amount of well recognized publications in international journals and its attractive training courses for water managers around the world. FRIEND has helped to bring up a new generation of scientists working together and sharing data, scientific knowledge and techniques across political borders and enhancing benefits of learning networks.
The FRIEND project has always advocated a
“bottom up approach”, with research objectives proposed by hydrologists in the region, and a steering committee providing a formal basis for maintaining co-operation and advancing links with both national and international research initiatives.
A generic overarching scientific objective has been to improve the understanding of the similarity and hydrological variability across different regions of
the world and to share models and techniques between countries, organisations and researchers.
The current research covers a divers range of topics including low flows, floods, variability of regimes, rainfall/runoff modelling, processes of stream flow generation, sediment transport, snow and glacier melt, climate change and variability and its uncertainties, and land-use impacts.
In recent years FRIEND has increased its efforts to establish training courses for water managers and academia. Subsequently, capacity building has become a high priority for the programme. Over 447 participants from 77 different countries have been trained on various topics like low flows, floods and droughts, climate change, GIS, hydrological modelling, water quality, database, sediments, and monitoring of mass balance of glaciers.
The sharing of data has always been given a high priority in the FRIEND programme. Through research activities, the FRIEND groups have established regional databases which have grown over the years and are regularly updated in order to meet new research challenges. Current activities concentrate on database harmonization and the establishment of an interface to provide Meta information on hydrological data and to facilitate access to hydrological data in different regions of the world.
Besides all constraints the FRIEND programme has faced over the past years, its broad and huge network of researchers, its excellent scientific record and its hydrological database, FRIEND is considered the most successful hydrological programme within the entire UN system and has created a new spirit of international cooperation across political boundaries.
The International Hydrological Programme (IHP) of UNESCO has hosted FRIEND for over 25 years, which is unusual in times of rapid changes;
UNESCO IHP is proud of the programme and thanks all the participating scientists and institutions for their excellent efforts over the years.
In the past decades, FRIEND has proven to be a very dynamic programme by taking up new research challenges and helping to improve our knowledge in regional hydrology under the threat of climate change. FRIEND has also been proactive in bridging the gap between science and practice and invested into capacity building and knowledge transfer at university and water manger level.
I would like to express my thanks to all the hydrologists, regional coordinators and national governments which have always enthusiastically provided the necessary support to ensure the success of the FRIEND project.
In particular, I thank Trevor Daniell (Global FRIEND Coordinator) from the University of Adelaide, Australia, for his wise leadership over the past years.
My sincere thank goes to Yan Huang, Changjiang Water Resources Commission, Wuhan, China, HKH FRIEND Coordinator, who, in close cooperation with UNESCO IHP in Paris and the contributions from the regional FRIEND coordinators and the support of the Regional UNESCO offices, has
compiled and edited this report. I also thank the regional coordinators for their great effort in compiling the input from their region. I am grateful to Ulrich Schröder and Andrea Wessler from the German IHP/HWRP Secretariat for their assistance and dedicated efforts in making the production of this report possible.
Siegfried Demuth
Chief Hydrological Processes and Climate Section UNESCO Division of Water Sciences
Foreword 3
1 Introduction 7
1.1 Introduction to FRIEND 7
1.2 Links with international projects and programmes 8
1.3 FRIEND Report 10
2 European (EURO) 12
2.1 Introduction 12
2.2 The European Water Archive (EWA) 16
2.3 Research Projects 18
3 Mediterranean (MED) 34
3.1 Introduction 34
3.2 The MED FRIEND database 35
3.3 Research Projects 37
3.4 Conclusions 43
4 Latin America and Caribbean (AMIGO) 44
4.1 Introduction 44
4.2 AMIGO FRIEND Database 45
4.3 Research Projects 45
4.4 Conclusions 45
5 Southern Africa (SA) 47
5.1 Introduction 47
5.2 The SA FRIEND database 48
5.3 Research Projects 48
5.4 Conclusions 49
6 West and Central Africa (AOC) 50
6.1 Introduction 50
6.2 The AOC FRIEND Database 51
6.3 Research Projects 51
6.4 AOC FRIEND general activities 51
6.5 Conclusions 51
7 Asian Pacific (AP) 52
7.1 Introduction 52
7.2 Asian Pacific Water Archive 52
7.3 Research Projects 53
7.4 Conclusions 56
8 The Hindu-Kush Himalayas (HKH) 60
8.1 Introduction 60
8.2 The HKH Website/Database 61
8.3 Research Projects 62
8.4 Conclusions 63
9 Nile Basin 64
9.1 Introduction 64
9.2 The Nile Database 65
9.3 Research Projects 65
9.4 Conclusions 71
10 Education and Training Programmes 73
10.1 European FRIEND (EURO FRIEND) 73
10.2 Mediterranean FRIEND (MED) 75
10.3 Latin America and Caribbean FRIEND (AMIGO) 75
10.4 Southern Africa FRIEND (SA) 75
10.5 West and Central Africa FRIEND (AOC) 75
10.6 Asian Pacific FRIEND (AP) 75
10.7 The Hindu-Kush Himalayas FRIEND (HKH) 76
10.8 Nile FRIEND (NF) 76
11 Conclusions 81
11.1 Key achievements 2006 – 2010 81
11.2 Strategic Plan for the Future 84
Annex 1 – FRIEND Coordinators 91
Annex 2 – FRIEND Research Participants 92
Annex 3 – FRIEND Meetings 2006 – 2010 110
Annex 4 – FRIEND Publications 2006 – 2010 114
Annex 5 – Useful Web Links 144
Abbreviations 146
Acknowledgements 149
1.1 Introduction to FRIEND
Water plays vital role in environment and human life.
At the same time, water crisis has been well recognised as an influential issue to sustainable environment and social-economic development. Facing new challenges such as human activity impact, climate change, increasing demands from social-economic development and the more appealing global changes, water management has been and will remain a difficult yet unavoidable task. The difficulties can be found in the increasing occurrence frequency of floods, drought and water pollution, more common and tense conflicts between different users due to lack of suitable water resources which might be caused by either water scarcity or water pollution, misuse of water resources and ineffective/inefficient water management practices resulted in depleted supplies, falling water tables, shrinking inland lakes and stream flows diminished to ecologically unsustainable levels etc. In addition, new challenges can be found in the increasing occurrence frequency and higher magnitude of hydrological extremes (floods and droughts) in comparing with historical records (e.g. recent serve floods occurred in China and Pakistan in 2010), such change of hydrological statistics would result in new challenges in operating and implementing the water works such as reservoirs, dikes and retention basins etc. The uncertainties associated with all those changes increases the risk in water management. To better facilitate water management, more specific and appropriate knowledge and technology should be adapted.
As an integrated approach, water management involves not only science, technology, physical conditions (such as climatologic and geological characteristics),
and policy, to some extend, but also cultural back- ground. As an integrated aspect, good similarities can be found at a regional level concerning the world which is formed by different regions. Thus, a regional cooperation aiming to sharing experiences and technology on water management has long been identified valuable and practical. As a result, a regional-based international scientific and technical programme, the Flow Regimes from International Experimental and Network Data (FRIEND) programme was launched in 1985.
Since its start with four European countries, the FRIEND programme has grown into a worldwide network of 8 regional groups, located in Europe (EURO FRIEND), the Mediterranean region (MED FRIEND), Latin American and the Caribbean (AMIGO FRIEND), Southern Africa (SA FRIEND), West and Central Africa (AOC FRIEND), Asian Pacific (AP FRIEND), the Hindu-Kush Himalayas including Central Asia (HKH FRIEND), and the Nile (NF) (Figure 1.1). In 2010 162 countries from around the world are participating in the programme (Table 1.1). Group members are drawn from opera- tional agencies, universities and research institutes.
Activities within regional FRIEND groups are determined locally since participants are best placed to identify the research priorities within their regions.
Taking on a problem-solving-oriented approach, outputs of the FRIEND projects can be applied directly to hazard mitigation and poverty alleviation strategies.
As international research programme, as well as a cross-cutting programme of UNESCO’s International Hydrology Programme (IHP), FRIEND helps to set up regional networks for analyzing hydrological data.
It aims to improve the understanding of hydrological variability and similarity across time and space – through the mutual exchange of data, knowledge and techniques at the regional level. FRIEND also provides support to researchers and operational staff of hydrological services in developing countries, thereby contributing to their capacity to assess and manage their own national water resources with various means such as training courses, workshops and joint projects etc.
FRIEND research covers a diverse range of topics including low flows, floods, variability of regimes, rainfall/runoff modeling, processes of streamflow generation, sediment transport, snow and glacier melt, climate change and land-use impacts.
Since 1985, there have been 6 phases of the FRIEND Programme. During all phases including the 6th phase (2006 – 2010), interest in FRIEND continues to grow and new projects have been emerged.
Through the programme development, it has been noticed that the advanced knowledge of hydrological processes and flow regimes gained through FRIEND helped to improve methods applicable in water resources planning and management. In particular, education and capacity development have become important components of the FRIEND programme, which has provided a number of opportunities for Figure 1.1 Location of FRIEND projects worldwide
people especially professionals from developing countries to learn and to exchange ideas.
1.2 Links with international projects and programmes
The FRIEND project is connected to many international programmes and projects within the international hydrological community. It contributes to
UNESCO’s programmes on global changes, to the International Flood Initiative (IFI), to the International Sediment Initiative (ISI) and to the education and capacity building programmes of IHP.
The project has a particularly effective relationship with the World Meteorological Organisation (WMO), through the Commission for Hydrology programme on disaster mitigation on floods and droughts, Hydrology and Water Resources Programme (HRWP) and the World Climate Research Programme (WCRP).
FRIEND also works closely with the International Association of Hydrological Sciences (IAHS) in
organizing conferences and workshops, as well as publishing conference proceedings. The EURO FRIEND project has a strong partnership with the Global Runoff Data Centre (GRDC), which hosts the European Water Archive (EWA), the data base of the EURO FRIEND consortium.
regional FrIend Groups Participating Countries european (euro)
(31 countries, established 1985 and reorganised 2009)
Albania Austria Belarus Belgium
Bulgaria Czech Republic Denmark Estonia
Finland France Germany Hungary
Iceland Ireland Latvia Lithuania
Luxembourg Moldavia Norway Poland
Romania Russia Serbia Slovakia
Slovenia Sweden Switzerland The Netherlands
Turkey Ukraine United Kingdom
Mediterranean (Med) (18 countries, established 1991 and reorganised 2009)
Morocco Algeria Tunisia Libya
Egypt Israel Lebanon Syria
Jordan Turkey Cyprus Greece
Albania Slovenia Italy France
Spain Malta
Latin American & Caribbean (AMIGo)
(41 countries, established 1999)
Anguilla Antigua and Barbuda Argentina Aruba
Bahamas Barbados Bermuda Bolivia
Brazil British Virgin Islands Cayman Islands Chile
Colombia Costa Rica Cuba Dominica
Dominican Republic Ecuador French Guiana French West Indies
Grenada Guyana Haiti Honduras
Jamaica Mexico Montserrat Netherlands Antilles
Panama Paraguay Peru Puerto Rico
Saint Kitts and Nevis Saint Lucia St Vincent &
The Grenadines
Suriname Trinidad and Tobago Turks and Caicos Islands US Virgin Islands Uruguay Venezuela
southern Africa (sA) (12 countries, established 1991)
Angola Botswana Lesotho Malawi
Mauritius Mozambique Namibia South Africa
Swaziland Tanzania Zambia Zimbabwe
west & Central Africa (AoC) (18 countries, established 1992)
Benin Burkina Faso Cameroon Congo
Gabon Ghana Guinea Cote d’Ivoire
Liberia Mali Mauritania Niger
Nigeria Central Africa Republic Senegal Sierra Leone
Chad Togo
Asian Pacific (AP)
(31 countries, established 1997)
Australia Cambodia China Cook Islands
Democratic Peoples
Republic of Korea East Timor Federated States of
Micronesia Fiji
Indonesia Japan Kiribati Maldives
Mongolia Myanmar Nauru New Caledonia
Pacific Islands:
American Samoa Republic of Korea Laos Malaysia
New Zealand Niue Papua New Guinea Philippines
Samoa Solomon Islands Thailand Tonga
Tuvalu Vanuatu Vietnam
the Hindu-Kush Himalayas (HKH)
(12 countries, established 1996 and reorganised 2007)
Afghanistan Bangladesh Bhutan China
India Kazakhstan Kyrgyzstan Myanmar
Nepal Pakistan Tajikistan Uzbekistan
nile (nF)
(6 countries, established 1996)
Egypt Ethiopia Kenya Sudan
Tanzania Uganda
Table 1.1 Countries participating in the FRIEND Programme
1.3 FRIEND Report
This volume is the sixth in a series of FRIEND Reports (Gustard et al., 1989; Gustard, 1993;
Oberlin and Desbos, 1997; Gustard and Cole, 2002;
Servat and Demuth, 2006), which have been produced to mark the end of successive phases of FRIEND and to coincide with major international FRIEND Conferences held in Bolkesjø, Norway, in 1989, Braunschweig, Germany, in 1993, Postøjna, Slovenia, in 1997, Cape Town, South Africa, in 2002 and Havana, Cuba, in 2006 (Roald et al., 1989; Seuna et al., 1994; Gustard et al., 1997; Van Lanen and Demuth, 2002; Demuth et al., 2006). This report presents research conducted during the sixth phase of FRIEND from 2006 to 2010 and coincides with the 6th World FRIEND Conference, Global Change – facing Risks and Threats to Water Resources, in Fez,
Morocco, 25 – 26 October 2010.
The report presents a synthesis of the global FRIEND research, providing the reader with a wide range of research activities addressed and different problems faced by each regional FRIEND group. Following the introduction (Chapter 1), Chapter 2 to Chapter 9 are devoted to each of the eight regional FRIEND projects. Each chapter was prepared by the regional FRIEND coordinators and project leaders, based on contributions from regional members. They typically describe the hydrological challenges faced in the region, project development, and an outline of the activities undertaken and selected examples of its research output. Chapter 10 gives an overview of the FRIEND education and training programmes;
Chapter 11 provides a general conclusion, summarizes the key achievements and outlines future plans for each of the FRIEND group.
Annexes give background information on the FRIEND project: contact details for the eight regional coordi- nators (Annex 1), FRIEND research participants (Annex 2), FRIEND meetings (Annex 3), and publications by FRIEND participants (Annex 4).
Although it is impossible to provide a fully comprehen- sive picture of all regional groups, these annexes show clearly the vigour, high productivity and wide-ranging nature of the FRIEND research and collaboration, and the wide dissemination of research results in scientific journals, conference proceedings, books and reports.
From the contributions to the Global FRIEND report, it has to be noted, however, that some regional groups
are more active than others. Future plans includes the motivation and stimulation of regional FRIEND Group activities through UNESCO in close cooperation with the regional coordinators.
References
Demuth, S., Gustard, A., Planos, E., Scatena, F., Servat, E. (Eds.) (2006) Climate Variability and
Change – Hydrological Impact. Vth International FRIEND World Conference, 27 November 1 December 2006, IAHS Publ. 308,
Gustard, A., Roald, L.A., Demuth, S., Lumadjeng, H.
and Gross, R. (1989) Flow Regimes from Experi- mental and Network Data (FREND). Institute of Hydrology, Wallingford, UK.
Gustard, A. (Ed.) (1993) Flow Regimes from International Experimental and Network Data
(FRIEND), Vol. I, Hydrological Studies; Vol. II, Hydrological Data; Vol. III Inventory of stream- flow generation studies. Institute of Hydrology, Wallingford, UK.
Gustard, A., Blazkova, S., Brilly, M., Demuth, S., Dixon, J., van Lanen, H., Llasat, C., Mkhandi, S.
and Servat, E. (Eds.) (1997) FRIEND ’97 – Regional Hydrology: Concepts and Models for Sustainable Water Resource Management. IAHS Publ. 246.
Gustard, A. and Cole, G. (2002) FRIEND – a global perspective 1998 – 2002. Institute of Hydrology,
Wallingford, UK.
Oberlin, G. and Desbos, E. (1997) Flow Regimes from International Experimental and Network Data
(FRIEND). Third Report: 1994 – 1997. Cemagref Éditions, France.
Roald, L., Nordseth, K. and Hassel, K.A. (Eds.) (1989) FRIENDS in Hydrology, Proc. Intl. Conf.,
Bolkesjø, Norway. IAHS Publ. 187.
Seuna, P., Gustard, A., Arnell, N.W. and Cole, G.A.
(Eds.) (1994) FRIEND: Flow Regimes from International Experimental and Network Data, Proc. Intl. Conf., Braunschweig, Germany. IAHS Publ. 221.
Servat, E. and Demuth, S. (2006) FRIEND – a global perspective 2002 – 2006. IHP/HWRP-Sekretariat,
Bundesanstalt fuer Gewässerkunde, Koblenz, Germany.
UNESCO/WMO (1999) Fifth International
Conference on Hydrology, Geneva, 8 – 12 February, 1999.
van Lanen, H.A.J. and Demuth, S. (Eds.) (2002) FRIEND 2002 – Regional Hydrology: Bridging
the Gap between Research and Practice, Proc. Intl.
FRIEND Conf., Cape Town, South Africa. IAHS Publ. 274.
2.1 Introduction
2.1.1 Regional Characteristics
The combined influences of latitude, topography and distance to the sea results in a widely varying distribution of precipitation across Europe,
ranging from less than 400 mm year-1 in parts of the Mediterranean region and Central Europe to over 1000 mm year-1 along the Atlantic shores from Spain
to Norway, the Alps and their eastern extension. Much of this precipitation is lost as evapotranspiration. The remaining recharge in some parts of Southern Europe is lower than 50 mm year-1 (JRC, 2006). Recharge determines river flow and catchment characteristics, such as soils and hydrogeology and lakes, control its temporal distribution. Average river flow across Europe is about 450 mm year-1, but this varies significantly, ranging from less than 25 mm year-1 in areas such as Southern Spain to over 3000 mm year-1 in parts of the Atlantic Coast and the Alps. Seasonal variation in river
flow varies throughout Europe. In the south, for example, river flow may be minimal during the summer months followed by occasional and intense rainfall events that result in dramatic but short-lived rises in river flow. In West Europe there is much less variation in flow throughout the year owing to the Atlantic maritime climate. In the Nordic countries and
Central and East Europe much winter precipitation falls as snow and a large proportion of river flow thus occurs during spring snowmelt.
The total renewable fresh water resource of a region is the total volume of groundwater recharge generated annually by precipitation within the region, plus the difference between inflow of rivers coming from and going to neighboring territories. The European
Environmental Agency (EEA, 2009) reports that the total freshwater resource across Europe water is relatively abundant. Only 13 % of this resource is abstracted, which would suggest that there is sufficient water available to meet demands and that European citizens do not suffer from the water shortages and poor water quality as experienced in many other regions of the world. However, both water and population are unevenly distributed in Europe. As a result, some countries and sub-regions experience water scarcity (i.e. water use higher than total renewable fresh water resource). In water-scare regions, overexploitation poses a threat to Europe’s water resources and challenges integrated water resources management. Reduced river flows, lowered lake and groundwater levels and the drying up of wetlands are widely reported. This also has a detrimental impact upon ecosystem services offered by aquatic habitats and freshwater ecosystems.
One indicator of water scarcity is the Water Exploitation Index (WEI), which is calculated annually as the ratio of total freshwater abstraction to the total renewable resource. A WEI above 20 % implies that a water resource is under stress and values above 40 % indicate severe water stress and clearly unsustainable use of the water resource (Raskin et al., 1997). Figure 2.1 gives the WEI for countries in Europe. Numbers are provided for 1990 and 2002, which illustrates development, in particular of water abstraction.
Water resources at risk in 2002 (WEI > 20) are in Cyprus, Bulgaria, Spain, Malta, Italy and England and Wales. The WEI decreased in 17 countries in the
period from 1990 to 2002, representing a considerable decrease in total water abstraction. Most of the decrease occurred in the new EU Member States, as a result of the decline in abstraction in most economic
sectors. However, six countries (the Netherlands, England and Wales, Greece, Spain, Portugal, and Turkey) increased their WEI in the same period
because of the increase in total water abstraction.
Furthermore, national estimates do not always reflect severity of water scarcity in some sub-regions. For example, Andalusia (ES), Sado (PT), Segura (ES) and Vouga (PT) have WEIs over 100 (EEA, 2009).
Drought can induce temporary water scarcity or aggravate more permanent scarcity. Drought is a natural phenomenon caused by climate variability.
Over the past 30 years, Europe has been affected by a number of major droughts, most notably in 1976,
0% 10% 20% 30% 40% 50% 60%
Iceland Latvia Slovakia Sweden Finland Slovenia Luxembourg Denmark Austria Switzerland Hungary Estonia Netherlands Czech Republic Greece Lithuania Portugal Turkey Romania France Poland Germany England and Wales Italy Malta Spain Bulgaria Cyprus
Total abstraction/Long term renewable resource WEI02 WEI90
Figure 2.1
Water exploitation index (WEI) for European countries in 1990 (WEI 90) and 2002 (WEI 02), (Source: EEA).
1989, 1991, and more recently, the prolonged drought over large parts of the continent associated with the 2003 summer heat wave. The most serious drought in the Iberian Peninsula in 60 years occurred in 2005 (EEA, 2008). However, there is no evidence that river flow droughts have become more severe or frequent over Europe in general in recent decades (Hisdal et al., 2001), nor is there conclusive proof of a general increase in summer dryness in Europe over the past 50 years due to reduced summer moisture availability (van der Schrier et al., 2006). Despite the absence of a general trend in Europe, there have been distinct regional differences (e.g. Hisdal et al., 2001;
Hanneford and Marsh, 2006; Lang et al., 2006).
Clearly, water management in Europe does not only face water shortage challenges, but also wet conditions, including high river flows and floods.
Figure 2.2 gives the number of floods in Europe over the last 10 years. Some areas have
been more affected than others. In the last decade the Lower Danube region, south-Eastern France, Central and Southern Germany, Northern Italy, and Eastern England experienced the highest number of repeated flooding.
Europe’s fresh water resources and hydrological extremes will likely be affected by climate change.
For the coming decades, global warming is projected to further intensify the hydrological cycle, with impacts that will probably be more severe than those so far observed (e.g. Bates et al., 2008). Precipitation in Europe generally increased over the 20th century, by 6 – 8 %. Large geographical differences occur, notably a reduction in the Mediterranean and Eastern Europe (EEA, 2008). In addition, some seasonal changes have occurred, notably an increase in winter
precipitation for most of Western and Northern Europe and a decrease in Southern Europe and parts of Central Europe. Climate models predict a general future increase in annual precipitation in Northern Europe and a decrease in Southern Europe (Figure 2.3).
The panels show for 4 different climate models the projected changes in annual precipitation. All maps show an increase in Northern Europe and a decrease in Southern Europe. The spatial pattern projected by each climate model remains the same over different emission scenarios, only the size of the changes varies (EEA, 2008).
Change in precipitation and likely higher temperature are projected to lead to major changes in annual and seasonal water availability across Europe. Renewable fresh water resources generally are projected to increase in northern regions. Southern and south- eastern regions, which already suffer most from water stress, will be particularly exposed to reductions in water resources (EEA, 2008).
More frequent and intense droughts are predicted across much of Europe over coming decades. For instance, in Southern Europe the maximum number of consecutive dry days is projected to increase substantially during the 21st century, whilst in Central Europe it will slightly increase. Lehner et al. (2006) showed that for Spain and Southeast Europe major droughts (i.e. droughts that have a return period of 100 year under the current climate) are likely to
become more frequent. In association with projected higher demands of water for irrigation, these more Figure 2.2 Number of flood events (EEA, based on data
from Dartmouth Flood Observatory (http://www.dartmouth.edu/~floods/).
Flood events, 1998 – 2008 Number of events
1 2
3 4
5
> 6
Annual precipitation change for IPCC A2 emission scenario, 2071–2100 compared to 1961–1990 Calculated with four climate models (HadCM3, NCAR-PCM, CSIRO2, CGCM2)
–25 –20 –15 –10 –5 0 5 10 15 20 25 >25
% anomaly
Outside report coverage
HadCM3 NCAR-PCM CSIRO2 CGCM2
Figure 2.3 Changes in annual precipitation for the IPCC A2 scenario (2071 – 2100 compared with 1961 – 1990) for four different climate models (Schröter et al., 2005).
vulnerable regions are most prone to an increase in drought risk and water scarcity problems. Thus regions in Europe that are already dry now are projected to become even drier (EEA, 2008).
Additionally, the Nordic countries and other snow- affected regions will experience a further shift of the flow regime due to global warming. This often implies higher winter flows and lower summer flows leading to more frequent and intensive summer drought (e.g.
Hisdal et al., 2007; Bates et al., 2008).
On the other hand, an increase in extreme high river flows is projected for large parts of Europe due to the increase in heavy rain events. Although there is as yet no proof that the extreme flood events of recent years are a direct consequence of climate change, they may give an indication of what can be expected: the frequency and intensity of floods in large parts of Europe is projected to increase (Lehner et al., 2006).
In particular, flash and urban floods, triggered off by local intense precipitation events, are likely to be more frequent throughout Europe. Flood hazard will also probably increase during wetter and warmer winters, with more frequent rain and less frequent snow.
Even in regions where mean river flows will drop significantly, as in the Iberian Peninsula, the projected increase in precipitation intensity and variability may cause more floods. In snow-dominated regions (Nordic countries, mountainous regions), spring snowmelt floods are projected to decrease due to a shorter snow season and less snow accumulation in warmer winters. Quantitative projections of changes in precipitation, river flows, drought and floods at the river basin scale remain, however, highly uncertain, due to the limitations of climate models, as well as scaling issues between climate and hydrological models (EEA, 2008; Bates et al., 2008).
In summary, Europe’s renewable fresh water resources are abundant, but not evenly distributed over Europe.
Many areas suffer from water scarcity and/or poor water quality. This challenges European’s water managers, in particular because they also have to cope with water demands associated with a growing population and extreme situations (drought and floods), which are likely to become more extreme in the future. EURO FRIEND’s researchers have significantly contributed to enhance the knowledge on spatial and temporal variability of hydrological regimes across scales, including providing a better understanding on the occurrence of droughts and floods under a changing climate, assessment of
renewable water resources, and human impacts under current and future climate, which helped to develop water policies (i.e. EU Water Framework Directive) and sustainable water resources management plans.
2.1.2 EURO FRIEND Project
In 1985 the FRIEND project was initiated by a few hydrologists from Germany, the Netherlands, Norway and the United Kingdom working together at the Centre for Ecology and Hydrology (former Institute of Hydrology). This was the birth of an international programme which developed into a worldwide FRIEND programme. The nucleus of FRIEND was built by the Northern Europe FRIEND project (NE FRIEND).
At the FRIEND Inter-Group Coordination Committee meeting (FIGCC) in Adelaide, Australia, 19 April 2008, the Regional Coordinators and a representative from UNESCO decided to implement a new structure of the Regional FRIEND groups, because the current structure is not appropriate to meet the new challenges and needs anymore in Europe. It was agreed to extend the countries of NE FRIEND project towards the Balkan and Black Sea countries. The name of the FRIEND Regional Group changed from Northern Europe FRIEND project (NE FRIEND) to European FRIEND (EURO FRIEND). This leads to a EURO FRIEND group that consists of 31 countries: Albania, Austria, Belarus, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Iceland, Ireland, Latvia, Lithuania, Luxembourg, Moldavia, Norway, Poland, Romania, Russia, Serbia, Slovakia, Slovenia, Sweden, Switzerland, the Netherlands, the United Kingdom, Turkey and Ukraine. The EURO FRIEND project coordinators discussed the integration of the former AMHY FRIEND and NE FRIEND project groups working on the same topic on a meeting in Koblenz, Germany, 30 May 2008. This applied in particular to the Low Flow and Drought groups, which already cooperated (e.g.
through joint meetings). The former AMHY FRIEND (Black Sea and Balkan countries) and NE FRIEND project groups working on Low Flows and Drought met in Bratislava, 10 – 12 November 2008 and they agreed on a joint work plan and elected a new project coordinator for the EURO FRIEND project on Low Flows and Drought.
The EURO FRIEND general objective is to study spatial and temporal variability of hydrological regimes at a European scale and in other regions beyond Europe.
The European FRIEND Group consists of five project groups covering four research themes including the development and update of a hydrological database, the European Water Archive (EWA). The four research themes are:
1. Low flow and drought, which focuses on drought propagation from meteorological droughts to hydrological droughts, space-time development of drought at different scales (including its characterization), hydrological droughts and their climatic drivers and human impacts,
2. Large-scale hydrological variations, which investigates hydrological variability and changes in space and time (including forecasting), multi-scale hydrological systems, large scale climate-hydrology interactions (including tele-connections), modeling of hydrological fluxes and water budgets at large scales, 3. Techniques for extreme rainfall and flood runoff
estimation, e.g. real time forecasting of extreme rainfall and floods, simulation for design purposes (frequency estimation of peak flows and flood inundation), further development of an uncertainty framework, and
4. Catchment hydrological and biogeochemical processes in a changing environment, which contributes to a paradigm shift in contemporary hydrology, moving from ‘hydrograph mimicking’
through calibration to ‘process understanding’.
The latter theme concentrates on comprehensive monitoring of water and solute states and fluxes in small experimental catchments with a focus on how they travel through the catchment, i.e. flow paths, residence times and runoff generation, including water quality, and impacts of projected climate and land use changes. Each project is led by a single individual (project coordinator) who is responsible for coordinating group activities, such as technical workshops, training courses and meetings, coordinating the scientific direction of the group’s research and representing the group at meetings of the EURO FRIEND Project Coordinator Group and the EURO FRIEND Steering Committee. The individual project groups working on the research themes comprise of about 20 – 40 scientists from different European countries, who meet regularly either at side meetings during conferences (e.g. annual European Geosciences Union (EGU) Assembly in Vienna, Austria) or at their own venues (on average every two years) to report about ongoing research work and to share knowledge,
experiences and ideas. Some of the project groups have created sub-groups on particular topics.
The EURO FRIEND project has developed a very strong international research network which reaches far beyond the boundaries of Europe. That enables the various groups to interact with other regional FRIEND groups on specific topics and opens up research to be conducted at various geographical and climatic regions. This helps to test and exchange methodologies at a continental and global scale.
The network was also very beneficial for obtaining substantial funding from the European Union (i.e. FP6-WATCH and FP7-XEROCHORE projects).
The five project groups use a bottom-up approach, implying that they develop their own research work plan. They receive advice from the European FRIEND Steering Committee (EURO FRIEND SC). The Committee, which meets every four years at the FRIEND Conferences, consists of representatives from each participating country’s national IHP committee, together with representatives from UNESCO, WMO, the European Research Basin network (ERB) and the European Environment Agency (EEA). The EURO FRIEND SC advices on
scientific directions, discusses options for dissemination of FRIEND research (e.g. conferences, journals), cooperation between FRIEND and other international programmes and organizations, for example, WMO- HWRP-CHy (Commission for Hydrology), IAHS-PUB, World Water Assessment Programme (WWAP), UN Water and EU. Furthermore, there is a strong link between the EURO FRIEND group and the various commissions of IAHS (International Association of Hydrological Sciences). The EURO FRIEND coordinator ship has been transferred from the IHP/
HWRP Secretariat at the Federal Institute of Hydrology, Germany to Wageningen University, the Netherlands.
2.2 The European Water Archive (EWA) The European Water Archive (EWA), one of the key features of EURO FRIEND, is hosted by the Global Runoff Data Centre (GRDC) at the Federal Institute of Hydrology in Koblenz, Germany. It builds upon work that has been initiated in 1985.
During 2007 a new data model was developed for the EWA. This model is similar to the GRDC data model allowing optimized data imports, management and extraction. Database tools developed and utilized for the GRDC database are now also being applied to
manage the EWA. This practice is simplifying the operational management of the different databases.
Now metadata catalogues and Google Earth kmz files are produced routinely after major EWA updates.
These facilities are provided on the EWA webpage (EWA webpage is on the GRDC website:
http://grdc.bafg.de) to allow data-users to identify suitable discharge stations relevant to their particular studies, when ordering data from the GRDC. Although the same database management tools are being used, the EWA is maintained in a separate database, according to FRIEND requirements.
During early 2008 the EWA dataset was successfully transferred form the old structure into the new data model. At that stage a clean-up of the database was carried out allowing the identification and removal of all stations registered in the database, without associated river discharge or other relevant data.
This cleaning procedure resulted in a decrease in the number of stations in the database. Both the data model and the database were presented at the EURO FRIEND Database Group Workshop held in Koblenz
from 28 – 30 May 2008. Questions arising from the transfer of data from the old to the new EWA database were also discussed and clarified at that meeting.
Currently the EWA contains river discharge and related metadata for more than 3800 stations from 29 European countries. The distribution of the stations is shown in Figure 2.4. The EWA is one of the most comprehensive river flow archives not only in Europe but also worldwide and it provides access to a spatially extensive long-term river discharge dataset from predominantly natural catchments. As such it remains the fundamental prerequisite for developing a better understanding of the temporal and spatial variability of hydrological regimes in Europe.
After the successful transfer of the EWA to the new database the focus has moved to improving the data acquisition strategy so that the EWA is updated with more recent historical river discharge data. At the May 2008 EURO FRIEND Database Group Workshop, the river discharge data requirements for
the EURO FRIEND Projects 2 – 5 have been identified.
Figure 2.4 Spatial distributions of stations in the EWA across Europe.
The different EURO FRIEND Projects have diverging river discharge data requirements in terms of spatial and temporal resolution and gauged catchment size. To address the needs of the different research communities a flexible data acquisition strategy is required, that includes scientists, EWA Focal Points and the operators of the EWA to negotiate data updates with the Data Providers. The EWA operators together with the EWA Focal Points are trying to institutionalize data updates for countries where data is being shared freely. For project specific datasets the individual scientists have the responsibility to obtain the data from the Data Providers and also provide them to the EWA operators.
Applying this rule, data imports and updates for the following countries have been completed or started since 2007: Sweden, Norway, Finland, Denmark, Czech Republic, Austria, Switzerland, United Kingdom and Germany. Scientists, EWA Focal Points and the GRDC together with the Data Providers have been instrumental in this updating procedure. With these updates available in the EWA an increasing number of researchers have been requesting river discharge data.
Data in the EWA is only accessible to scientists associated with EURO FRIEND programme.
The data policy remains unchanged, but the process
how best to obtain the data has been formalized and described and also put in a graphical flowchart as shown in Figure 2.5.
A positive trend has been recognized amongst data providers. In several cases data are now provided to the GRDC for use both in the EWA and in the GRDC database without restricting the dataset to the one or other database. This enables the GRDC to provide more suitable datasets to the research and scientific community. The future emphasis will remain on more frequent updates of the datasets and an improved spatial coverage.
2.3 Research Projects 2.3.1 Low Flow and Drought
Drought as a natural, recurrent feature of climate is initiated by prolonged dry and warm weather. It causes less than normal water availability which influences ecosystem services, but also many other sectors of economy (e.g. agriculture, energy, navigation and health). Drought develops slowly and has much longer duration than the opposite hydrological extreme, i.e. the floods (Section 2.3.3).
EWA
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EWA data request procedure
Figure 2.5 Data request
procedure for EWA data by EURO FRIEND
affiliated researchers.
The EURO FRIEND project on Low Flow and Drought was established on 10 November 2008 during a joint meeting of the former NE FRIEND Low Flow Group and AMHY Low Flow and Drought Group in Bratislava, Slovakia. It has 39 active members from 16 countries (Annex 2).
The research project on Low Flows and Drought includes the following research topics:
Drought generating processes,
Space-time patterns and its characterization,
Drought indices,
Large-scale drivers, and
Human impact on drought including global change.
The research topics have been jointly studied by smaller research groups, created mainly within international projects. Examples are different sub-groups, WATCH, XEROCHORE, IAHS-PUB, COST733 and the WMO-Low Flow Manual Low Flow subgroup. WATCH and XEROCHORE are EU funded projects. Project members actively participated in many international events presenting research
results. The most important were: IAHS Assemblies in Perugia (2007), Hyderabad (2009), EGU Assemblies in Vienna (2007; 2008; 2009), Water and Climatic conferences (Helsinki 2007) and others (Annex 4).
Comprehensive research is going on in the field of drought propagation through the hydrological cycle (transformation from meteorological drought to hydrological drought). This is done in various catchment across Europe with different climate and physical catchment structures (e.g. van Lanen, 2006;
Machlica et al., 2008; van Loon et al., 2008).
Drought propagation is also studied at a global scale using large-scale forcing data and a synthetic modeling approach (van Lanen and Tallaksen, 2007;
2008). Fleig et al. (2006) give a very thorough analysis of streamflow drought across the world by using river flow data from a global dataset. Progress is made in the characterization of the space-time development of drought at different scales. For instance, Tallaksen et al. (2009) provide a methodology and illustrates it with the space-time development of meteorological and groundwater drought for the Pang catchment (UK).
0 0,5 1 1,5 2 2,5
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Figure 2.6 Groundwater drought indices for the Nitra River Basin (Slovakia).
Investigation on improved drought indices has continued (Fendekova et al., 2009). Figure 2.6 shows the base flow duration curve for individual years, which are used to define a new base flow index.
Investigation of the correlation between Weather Types (WTs) and a regional drought index shows the potential to link large-scale climate drivers and drought for UK and Denmark (e.g. Fleig et al., 2008).
In this respect, large-scale drivers, tele-connections and synchronicity are studied (joint activity project groups Low Flow and Drought and Large Scale Hydrological Variation, see also Section 2.3.2).
Human influences, including climate change impact on low flows and drought Hisdal et al. (2007) studied spatio-temporal changes in historical river flow and climate data in the Nordic countries. The observed increase in temperature strongly affects the hydro-logical regimes Signals. Van Lanen et al.
(2007) reviewed the impact of climate change on drought for the EC Communication on Water Scarcity and Drought. Stahl et al. (2008) reported about temporal trends and spatial patterns in the occurrence and severity of low flows and hydrological droughts across Europe. Streamflow data were brought together from small undisturbed catchments in a number of EU countries. The European Water Archive (EWA) (Section 2.2) has been updated to the year 2005 to include recent severe droughts.
The results provided the opportunity to compare to an earlier study that was based on data of an earlier version of the archive for the periods of 1930 – 1990 and 1962 – 1990 (Hisdal et al., 2001). Figure 2.7 shows changes in one of the investigated low flow indices, i.e. the mean annual 7-day minima, AM(7) is commonly used.
Tokarczyk and Jakubowski (2006) assessed minimum river discharge and associated water resources under different climatic conditions for Poland.
The project group has been heavily involved in synthesizing and dissemination of knowledge on low flows and drought. Many members contributed to the WMO Low Flow Manual (Gustard and Demuth, 2009)
and the Guidance Document on Drought & Natural System in the framework EU-Funded project XERO- CHORE (Wipfler et al., 2009) and are providing input to the chapter Low Flow Estimation (Laaha et al., in prep.) for the IAHS-PUB report on Runoff Prediction in Ungauged Basins – a Benchmark Assessment.
Figure 2.7 Trends in mean annual 7 day minima, AM (7) (Stahl et al, 2008).
European Drought Centre (EDC)
Members of the Low Flow and Drought group have close links to the European Drought Centre (EDC).
The idea of a European network of experts on drought research and mitigation was strongly encouraged through the FRIEND project (UNESCO- IHP) and the EU supported ARIDE project (2001), and finally made explicit in the ASTHyDA project (2005). The European Drought Centre was formally established at the joint NE FRIEND and AMHY Low flow meeting held in Bratislava in May 2004.
The EDC is a virtual centre of expert groups and organizations in Europe working in drought research or management. Although the key task is to establish the essential European dimension of the centre, it will also link with other international projects, organizations and experts outside Europe thereby enable and promote stronger international cooperation.
In the period 2007 – 2009, EDC was primarily supported by EU funding, i.e. the WATCH and the XEROCHORE projects. By the end of 2009, about 170 drought experts were member of the EDC.
An important feature of the EDC is the website, which is hosted by the University of Oslo. It provides news on drought activities (e.g. upcoming workshops and conferences, emerging initiatives) (Figure 2.8).
You can find links to the current drought situation in Europe (Europe Today). There is also a list with
key publications on drought and an archive with documents on some recent droughts. Over the reporting period, the functionality of the EDC website has been increased by: (1) creating a member database, (2) allowing EDC members to access the database through a web interface, (3) introduction of a request form for a dynamic database search that allows identification of subgroup of drought experts based on user-defined search criteria (e.g. fields of expertise, regions/countries or project membership), and (4) offering the opportunity to send emails to the selected subgroup of drought experts.
The research effort is targeted towards regional hydrology. More specific research themes include:
1. methods for investigating of hydrological variability and change in space and time, 2. multi-scale hydrological systems/scale issues, 3. large scale climate-hydrology interactions,
including tele-connections,
4. modelling hydrological fluxes/budgets and water use, and
5. prediction and forecasting of hydrological variability, including floods and droughts.
The research approach of the group is holistic.
Research spans the spectrum of hydrological descriptors (average, minimum (drought), maximum (floods), annual regimes, duration curves, moments etc.), rather than focusing upon certain aspects of the hydrological regime. Furthermore, several participants work on the atmosphere-surface water (including snow and ice)-groundwater process cascade and, thus, bridge traditional (sub-) discipline boundaries. It may be suggested that the benefit and unique aspect of EURO FRIEND Project 3 is the cross-cutting nature of research activities, which allow the group and participants to collaborate with AMIGO (Central America and Caribbean), MED (Mediterranean) and HKH (Hindu Kush Himalayan) FRIEND programmes, as well as other EURO FRIEND sub-groups.
Several participants have worked on advancing regionalisation, interpolation and time-series analysis methods and scaling issues. Sauquet et al. (2008) employed hydro-stochastic concepts to estimate mean monthly runoff at ungauged sites, using France as a demonstration region (Figure 2.9). The approach developed is consistent with the water balance along the river network; and it combines empirical orthogonal functions and an adapted stochastic interpolation scheme to match runoff data. The observation data are handled in a hydrological information system, which allows display of results either as change in a statistical parameter along the river network or as a map of the variation of the parameters across the basin.
Novel methods have also been developed to analyse:
(1) distribution of floods across Europe over the last 1000 years, including incorporation of historical
hydrological information into flood frequency analysis (MacDonald); (2) regional variability in hydrological/basin characteristics and flood frequency for small basins in Slovakia (Solín);
Figure 2.8 Homepage of the European Drought Centre with News (access data 27 November 2009).
2.3.2 Large Scale Hydrological Variations Given heightened concerns about climate change and human impacts upon water resources, it is critical to provide information about current and future variations in hydrological characteristics.
By elucidating patterns and drivers of hydrological response, it is possible to assess those regions and time-periods most susceptible to climate change/
variability and anthropogenic influences and, thus, inform decision-makers so that water related hazards and stress (e.g. floods and droughts) may be mitigated.
Thus, the aim of EURO FRIEND Project 3 is to identify and understand variations in hydrological behavior at a range of spatial (within-basin to global) and temporal (event to multi-decadal) scales.
(3) spatial variability of precipitation regimes across Turkey (Şaris; Hannah; Eastwood); and (4) trends across the full range of flow duration curve percentiles for Wales and the English Midlands (Dixon; Lawler).
A highly active area of EURO FRIEND Project 3 research is large-scale climate-hydrology interactions.
Researchers at the University of Rouen (Massei and Laignel) quantified River Seine precipitation and discharge variability over the last half-century and
assessed links with the North Atlantic Oscillation (NAO). LOESS filtering associated with continuous wavelet transform revealed the presence of a long- term trend, and 5 – 9 year and 17 year fluctuations (Figure 2.10). After removal of annual cyclicity in discharge, the detected trend and inter-annual modes linked to NAO were found to explain up to 23 % of total daily River Seine flow variance from 1950 – 2008.
Similar inter-annual variations as detected in Seine river flow were found in small watersheds and in the piezometric oscillations of the Chalk aquifer around the Seine estuary (Massei and Laignel). Depending on the hydrogeological context (notably thickness of surficial deposits and Chalk aquifer depth), a differential filtering of the climate-driven inter-annual modes of variability was produced (Figure 2.11).
The role of basin properties as a modifier of the climate signal in river flows was assessed more widely for 104 gauged basins across mainland Great Britain (Laizé; Hannah). In this study, regional climate (precipitation, potential evaporation, soil moisture deficit etc.) variables were found to have stronger association with seasonal flows than atmospheric circulation (NAO), with the best predictors varying with season.
Figure 2.9
Map of river flow regime based on the twelve reference hydrographs for France (Sauquet et al., 2008).
Ongoing research on large-scale climate- hydrology interactions is focused on the UK (Lavers; Prudhomme;
Hannah), Turkey (Şaris;
Hannah; Eastwood) and around the Mediterranean (Kordomenidi; Hannah).
GROUP 1
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Figure 2.10 Morlet continuous wavelet spectra of River Seine (a) daily discharge and (b) mean daily precipitation on the Seine watershed.
At an even larger spatial scale, climate-river flow links have been assessed across lowland and mountain environments of northern Europe (Kingston et al., 2009). As part of this work, an inverse climate-river flow relationship was found between northern and southern Scandinavian river flows that are explained by differences in the relative contribution of melt water to river flow between these regions, their latitudinal separation, and orographic effects on precipitation distribution (Figure 2.12).
Researchers at the UK Centre for Ecology and Hydrology (CEH) have evaluated the association between Circulation Types (CTs) and flood occurrence
across Europe. Relationships were assessed for 488 river basins, including data from the FRIEND Euro- pean Water Archive (EWA) and using CTs from 64 weather type catalogues developed within COST733 Action. Results showed variation in CT-flood
associations due to differences in flood generation mechanisms in different regions and the seasonal CT frequency (Prudhomme; Genevier).
As well as floods, the association between CT frequencies and the development of regional hydro- logical drought has been investigated for Great Britain and Denmark as part of COST733 Action (Fleig; Tallaksen; Hisdal; Hannah; Section 2.3.1).
Figure 2.11
Effect of geological setting, including the presence of karst, on the evolution of statistical descriptors: from top to bottom, lag (response)- time to precipitation, persistence (autocorrelation) and filtering capability of the hydro-system (spectral bandwidth) decrease.
In collaboration, CEH, the Walker Institute at University of Reading and water consultants JBA have explored coherence of drought in Europe using indicators of rainfall and stream flow deficit.
Correlation in drought occurrence between regions was found to be low generally; but multivariate analyses revealed broad continental-scale patterns possibly related to large-scale atmospheric circulation indices such as the NAO and the East Atlantic-West Russia pattern.
At the transcontinental scale, an inverse and lagged correlation has been identified for river flow in autumn between eastern North America and northern Europe (Kingston; Hannah; Lawler; McGregor;
Figure 2.13). These trans-Atlantic tele-connections are stronger than the temporal autocorrelation of autumn European river flow and suggest potential for using North American river flow as a harbinger (lead-time predictor) of European river flow.
Research on modeling hydrological fluxes/budgets and water use has focused recently on a developing a vulnerability index (VI) to quantify human vulnerability to climate change induced decreases of renewable groundwater resources (Figure 2.14).
Figure 2.12 Composite precipitation anomaly between November high minus low river flow years (1968 – 1997) for rivers in NW Norway, which is indicative of inverse correlation of river flow between NW and SE Scandinavia.
The new VI combines projected decrease of Ground- Water Recharge (GWR) with a sensitivity indicator
that is a composite of: a water scarcity indicator, an indicator for dependence of water supply on ground- water and the Human Development Index (Döll, 2009) change scenarios.
The prediction and forecasting of hydrological variability is a growing area of research within EURO FRIEND Project 3. The method of Bayesian merging developed to correct biases in climate model seasonal forecasts was adapted by CEH to evaluate the capability of Global Climate Model (GCM) to forecast Europe’s climate several month ahead. Precipitation hindcasts with 1- to 3-month lead time of seven ensemble runs developed for the European DEMETER project were compared with the ENSEMBLES gridded observational dataset and biases of each model assessed. Monthly hindcasts where merged with rainfall climatology according to the performances of their corresponding GCM to produce probabilistic ensemble forecasts.
These forecasts where disaggregated to a daily time- step using an analogue-based technique, generating 20-member ensembles time series for each grid, then input into the G2G gridded hydrological model (Dadson et al., 2008) to generate daily river flow hindcasts.
Figure 2.13 Composite 500 hPa geopotential height anomaly between October high and low river flow years for rivers in eastern North America, which is indicative of inverse correlation of river flow between eastern North America and northern Europe.
Figure 2.14 Vulnerability index VI showing human vulnerability to climate change induced decreases of renewable groundwater resources by 2055 for four climates.
Initial results show that the merged forecasts perform better than climatology for 1-month lead time; but, at a 3-month lead, biases are generally too large for forecasts to significantly outperform the climatology
Figure 2.15 (a) observed rainfall, (b) historical climatology, (c) Bayesian merged DEMETER hind casts ensemble mean and (d) river flow hind casts (in mm) for February 1995 (28 Feb for river flow).
(Figure 2.15). Additional research is ongoing on seasonal river flow forecasting using outputs from dynamical models, statistical models and combined approaches (Lavers; Prudhomme; Hannah).
