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Water Balance of the Republic of Croatia: Achievements and Necessities

Water Balance of the Republic of Croatia: Achievements and Necessities. OGNJEN BONACCI Faculty of Civil Engineering, University of Split, Matice Hrvatske 15, 21000 Split, Croatia obonacci@gradst.hr BOJANA HORVAT Hrvatske vode – VGO Rijeka, Đure Šporera 3, 51000 Rijeka, Croatia

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Water Balance of the Republic of Croatia: Achievements and Necessities

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  1. Water Balance of the Republic of Croatia: Achievements and Necessities OGNJEN BONACCI Faculty of Civil Engineering, University of Split, Matice Hrvatske 15, 21000 Split, Croatia obonacci@gradst.hr BOJANA HORVAT Hrvatske vode – VGO Rijeka, Đure Šporera 3, 51000 Rijeka, Croatia bojanah@voda.hr

  2. INTRODUCTION • Without an accurate water balance it is impossible to manage not only water resources but also a development of a country. When working on the water balance it is inevitable to face the fact that appearance of the water within a country is highly dynamic and variable process, both spatially and temporarily. Therefore, methodology, which is directly dependant on a time unit and is a function of measured hydrometeorological and hydrological data quality and data availability, is the most significant element. • Due to the human influence, change of his water needs and climatic variations and/or changes, water balance of an area cannot be taken as final. The process must constantly be monitored, controlled and updated. Major role of each water balance is long term sustainable management of water resources for a given area.

  3. International water legislation is developing rapidly and is stimulated by frequent conflicts connected with the use of international water resources. It is the fact that neither one of the countries today can have a full sovereignty in use of transit water resources but have to respect the rights of the neighbours. To be able to debate on a subject of rights it is necessary to have an accurate water balance synchronised with the neighbouring countries. • Water balance of each country is an important starting point for effective water resources management. At the same time, water balance avails in rights protection of a particular country on international level.

  4. METHODOLOGY • Since is the first systemised water balance of Croatia, the simplest methodology has been applied, based on 30-years averages for a time period 1961-1990. The water balance equation is as follows: I – O = DV where I is water entering Croatia, O is water leaving the country whileDV stands for the change in storage at the end of the observed time period. • Based on a chosen 30-years time period (1961-1990) and balancing the averages within a given interval, the assumption that changes in water storage will be zero (DV=0) can be made with high accuracy. Therefore, the equation (1) can be simplified into a following form: P – (Q + ET) = 0 where P is precipitation,Q is runoffand ET is evapotranspiration from the analysed area. This simplified water balance equation avoids and/or neglects consideration of certain variables and hydrologic processes, which is necessary due to highly variable and complex runoff on a territory of Croatia, spatially as well as temporarily.

  5. Next figure shows spatial distribution of precipitation for a time period 1961-1990. A map was made using Universal Kriging method. For that purpose, the data from 38 main meteorological, 110 climatological, 419 rain gauging stations and 22 totalizators has been used. In order to estimate the precipitation distribution in the boundary areas, the precipitation data from neighbouring countries had to be used. Number of gauging stations from each neighbouring country is as follows: Slovenia – 9, Bosnia and Herzegovina – 33 and Serbia and Montenegro – 12. Average precipitation of the observed time period is 1162 mm.

  6. CRITICAL REVIEW • Methodology, as well as, the accuracy of the accomplished results is dictated by the state of the available data, which varies from one watershed to another. The first obstacle is non-existence of a reliably defined boundary between Adriatic and Black Seas catchments. Different references offer different data and none of them is reliable. According to the divide adopted in our analysis, Adriatic Sea catchment covers 21 405 km², while Black Sea catchment covers 35 133 km² of the Croatian territory.

  7. Second problem is related to the accuracy of the precipitation definition. The 30-years average precipitation in Croatia adopted in this paper is 1162 mm. For the comparison, an estimation based on Thiessen polygons resulted in 1081 mm while the arithmetic average method gave a result of 1131 mm. The differences are not very significant but the problem still lies in the fact that non-corrected precipitation values were used for the analysis. For the purposes of the Hydrological Atlas of Switzerland which represents the bases for the water balance of Switzerland, the Swiss experts applied the precipitation correction over the Swiss territory and it is considered to be the most complete analysis so far. In average, the precipitation has been increased up to 14%. The values are in range from 4% (lowlands and flatlands) to 30% (Alpine area with significant amount of solid precipitation). The corrected results depend upon applied methods while the measured values are always smaller than the real quantities.

  8. The work on water balance of Croatia in general should be taken as a process that needs constant work and improvements, methodologically and in sense of accuracy. Average 30-years values cannot be taken as the final results. It is necessary to get into more subtle analysis of shorter time units and extreme events. The first step should be focused on the water balance of the selected dry and wet years.

  9. An important task is a preparation of new methodology for water balance definition based on a month as a time unit. Extremely variable distribution of precipitation in time and space caused insufficient water quantities in some parts of Croatia. A critical moment for water management is not only during the drought years but also every year during summer and vegetative months. This methodology should be oriented towards giving clear and reliable answers on strategic questions related to the water resources management issues.

  10. Natural distribution of water resources in Croatia both spatially and temporarily allows better, more effective and worth while use and management of water resources on entire territory. That cannot be accomplished without good water balance that can explain and accurately estimate all available water resources in space and in time. Water balance presented in this paper is just the first step.

  11. Thank you for your kind attention!

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