Cooperation of hydrologists from the Danube River Basin

The development of the hydrology of The Danube River Basin has a long tradition from nineteen century and beyond. Cooperation in hydrology science started 1961 and up to day, 28 conferences have been performed. Since 1975, cooperation between hydrologists of the Danube River Basin has been conducted within the framework of the International Hydrological Programme (IHP) of UNESCO and IHP National Committees established common Cooperation of the Danube 10 River Countries. In addition, Cooperation produce several reports and two books. Cooperation IHP Danube propose common statements for further research and appeal for development water station network necessary for measurement of anthropogenic and climate change impacts


Introduction
The development of the hydrology of The Danube River Basin has a long tradition. Data on water levels in catastrophic floods 15 have remained recorded at individual structures since medieval times (Pekarova et al., 2013). Hydrology began to develop more intensively after the Napoleonic wars in the first half of the 19th century. At that time, Bavaria and Austro-Hungarian countries began extensive hydraulics constructions on the regulation of watercourses. In 1826, the Kingdom of Bavaria erected 56 water meters and began systematic observations of the water level, and later in the second half of the 19th century a Hydrographical Bureaus and a similar service were organized in the Austro-Hungarian Monarchy (Schiller et al., 2010). An 20 extensive network of water stations and precipitation stations operated in middle of nineteen centuries in the Danube River  The IHP International Council, as well as its Secretariat at UNESCO headquarters, is responsible for the implementation of the IHP on a global scale and for monitoring and coordination of the implementation of particular program topics. Each country contributes to its own development by participating in the implementation of individual projects in the International Program, 45 within limits of its material and personnel capabilities. At the same time, the achievements of each country are available to other UNESCO member countries. This knowledge transfer is one of the essential components of UNESCO programs.
Since 1975, cooperation between hydrologists of the Danube River Basin has been conducted within the framework of the International Hydrological Programme (IHP) of UNESCO and IHP NC established common Cooperation of the Danube River

Countries. 50
Cooperation of experts from the Danube countries develops on two activities: • Organising regional scientific conferences of the Danube countries on hydrological forecasting, and • Deriving Regional hydrological scientific monographs and thematic projects related to the Danube River Basin.

The Danube River NC IHP Cooperation 55
At the beginning, cooperation was related to discharge forecast, but later on the research extended on hydrological bases of the water management. Cooperation began spontaneously on the basis of the needs of the basin countries, burdened by the political division of Europe during the Cold War. The first meeting was organized by the VITUKI Institute in Budapest in proportions are shown in Table 1. As the number of the Danube countries grew, this regional forecasting conference changed its name to Conference of the Danubian Countries on Hydrological Forecasting and Hydrological Bases of Water Management.
Successful participation in the presentation of national hydrological research at individual conferences triggered the start of joint research work. In order to improve the utilization efficiency of the Danube's water potential and upgrade flood protection, 75 the Danube countries launched an initiative in 1970 to begin the development of a Hydrological Monograph on the Danube River Basin. This initiative was consistent with one of the main objectives of the International Hydrological Decade of IHD UNESCO (1965UNESCO ( -1974, to encourage regional cooperation in the field of hydrology in international river basins. At the initiative of DC, work began on the preparation of the water balance of the Danube river basin. The idea was put forward in 1971. The work was then very ambitious, but proceeded very slowly because of the political burden and lack of logistics to 80 support such a project (Domokos, 2010).
The first outcome of the regional cooperation of the Danube countries in this regard was the publication of national During that period (from 1971 to 1986), experts from all eight Danube countries met every other year and coordinators each year, and agreed to create a single monograph for the entire Danube River Basin. Following harmonization of data and water 90 balance maps between neighbouring countries, the following publications were issued: 1. "Die Donau und Ihr Einzugsgebiet -Eine hydrologische Monographic" in German (München, 1986), and 2. "Donau i ego basseyn -Gidrologicheskaya Monografiya" in Russian, in Leningrad (RSPS 1989).
3. Representative monograph "Danube: hydrology of the river", printed in four languages (English, Russian, German and French) (Stančik A. and Jovanović, S. et al., 1988). 95 Cooperative work on the monograph has shown that river basin countries need to be more integrated and organized.
Representatives of IHP UNESCO NC decided at the meeting in April 1987 in Budapest to continue their cooperation organized https://doi.org/10.5194/hess-2020-66 Preprint. Discussion started: 9 March 2020 c Author(s) 2020. CC BY 4.0 License. under the umbrella of IHP UNESCO and adopted the basic principles of cooperation (Domokos 2008). Among other things, the working languages are German and Russian, at least one expert meeting per year is foreseen and currency coordination is foreseen. The political transition in the 1990s caused an increase in the number of countries in the basin. With the collapse of 100 socialist countries in Eastern Europe, new countries were formed in the Danube River Basin (now 19 in total), which also joined the regional cooperation effort under UNESCO IHP. In 2002, the Coordination of the NC IHP of the UNESCO Danube River Basin States updated the principles of cooperation. In principle, English is intended as the working language. Today, active participants in regional cooperation are National IHP Committees of the following countries: The work of experts from the Danube countries is carried out at regular working meetings (once a year in certain countries) and extraordinary working meetings (once in two yearsduring the Conference of the Danube Countries on Hydrological 110 Forecasting). The working meetings are managed by the country/expert coordinator selected at two-to-three year intervals, each time from another Danube country.

Achievements of cooperation NC IHP UNESCO of Danube River Basin
The monography "Hydrology of the River Danube" is until now the major integrated approach on water regime of the Danube 115 River and its tributaries. Inside the IHP UNESCO Committees cooperation, several common projects are going on supported by modest national sources.
In the period from 1993 to 2017, the above-mentioned Danube countries participated in the implementation of eleven thematic projects. So far, the following projects or subprojects have been completed and published as additional chapters of Monography, while some of the projects are in the process of implementation: Water is becoming an increasingly important subject of international cooperation that cannot be properly managed without the 170 necessary knowledge of the water regime and the impact of climate change. The monograph published in 1986 was produced on the basis of data until 1970. The monograph and many research reports need to be updated. That is why at the 17th meeting in the Golden Sands of 2017 we adopted a resolution on »Common statement from the participants of the XXVII Danubian Conference on hydrological forecasting and hydrological base of water management: 175 The scientists participating at the recent XXVII conference have agreed to adopt a common statement with respect to the urgent needs for further systematic and broadly integrated research in the Danube River Basin with the aim of comprehensive further water management research including climate change and anthropogenic impacts that have been emerging for the last centuries.
The common statement will be presented to relevant national and international governmental and public bodies responsible for water policy in the Danube River Basin. 180 The following topics should be analysed and evaluated:

1.
Update of the Danube River Basin water balance. Understanding the water balance is essential for protecting the Danube River Basin environment and for water management at large. Without knowledge of the water balance is it not possible to analyse climate change impacts or the transboundary impacts and anthropogenic activities.

2.
Improving water monitoring. Numerous water gauging stations have been abandoned due to budgetary cuts in some 185 countries, so there is less information available on the water regime than years or even decades before. Numerous new techniques were developed in the recent years and should be implemented. Evaluation of the impacts of climate change and anthropogenic changes cannot neither be justified nor confirmed or properly evaluated without comprehensive and reliable measurements.

3.
Water management in the Danube River Basin for extreme conditions. We do not know enough about extreme floods 190 and droughts, especially with respect to probable maximum events, of precipitation, floods and droughts. Without data, information and knowledge the magnitudes and implications of such extreme conditions are not known.

4.
Snow hydrology is quite well developed in some countries but not over the entire Danube River Basin. Without thorough monitoring and analysis of snow processes, estimates of the water balance and extremes are unreliable.

5.
Creating an inventory of the major water users (population, industry, agriculture, hydropower, navigation) and their 195 water needs.

6.
Testing and implementing improved methods and procedures for analysing of long duration floods and severe droughts, and designing structures and systems aiming at resilient and sustainable human settlements, infrastructure systems and industry complexes. 7.
An updated and refined study should test and extend the results published in the monography »Hydrology of the River 200 Danube« published more than 30 years ago.

8.
Hydrological understanding should be furthered in collaboration with other disciplines addressing demographic changes and climate change impacts, such as environmental, management forestry, navigation, development and housing, tourism and other sectors.

9.
Developing a roadmap for the goals of Water Security and other UN Goals for the coming decades, as given within 205 the IHP UNESCO VIII Phases Programme.

10.
Developing of common hydrological and hydraulics regional models for the entire Danube River Basin that are continuously updated as more information becomes available.

11.
Monitoring dams and dykes failure consequences related to critical infrastructures on the Danube River and its tributaries. 210

12.
Evaluation and assessment of historical floods in the past, aiming at critical analysis of the methods and procedures for modelling and design projects in multidimensional space, especially at river confluences, using the Balkan floods in the spring of 2014.

13.
Historical hydrological information is no less important than the current instrumental information. More efforts should therefore be invested in rescuing and digitizing such information (flood marks, archived data, and various other proxy 215 data) throughout the entire Danube River Basin. 14.
Establishing the concept of non-stationarity in the distribution of extreme hydrological and meteorological events as a basis for the definition of calculating hydrographs for the dimensioning of hydro technical facilities that would incorporate anthropogenic influences and the influences of climate change.
At the XXVIII meeting in Kyiv, we adopted an appeal to increase terrestrial measurements: »We gained insight into the 220 hydrological circle owing to terrestrial measurements of the individual components of water cycling: precipitation, surface water level and discharge, velocity, air and water temperature, groundwater table, stream flow, evapotranspiration, transpiration, soil moisture, etc. Remote sensing gave new impetus overall and provided the assessment of spatial distribution of the various phenomena. State-of-the-art technology provided measuring probes equipped with computer memory and wireless connection. This development has allowed us to carry out complex hydrological measurements and observations with 225 much smaller resources than in the past. Environmental protection and the expected climate change pose new challenges and require additional, more detailed measurements. Unfortunately, in the Danube River Basin we have witnessed a reduction in the measuring sites for hydrological and meteorological measurements. During the economic crisis that began over a decade https://doi.org/10.5194/hess-2020-66 Preprint. Discussion started: 9 March 2020 c Author(s) 2020. CC BY 4.0 License. ago, there were reductions in financial resources in the national services in charge of the measurements mentioned. Many measuring points were abandoned and never restored. The requirements to monitor the various anthropological impacts, 230 environmental protection, and climate change require an increase in the number of measuring points and the introduction of new measuring technologies into practice.
Therefore, the participants of IHP UNESCO's 28th Conference of the Danube Countries appeal to the governments from the Danube River Basin to stop the process of reducing measuring points but, on the contrary, to increase their number. In fact, without additional water stations, realization and our projections of climate change and anthropogenic impact will have higher 235 uncertainty.
A XXIX conference in the Czech Republic is scheduled for 2021. Further research is also envisaged regarding the river temperature regime, low flow rates, etc. Research reports and conferences are digitized and available on the co-operation website.