RISK ASSESSMENT OF EXTREME EVENTS ALONG RIVER FLOWS IN BULGARIA USING INTEGRAL INDICES

The present work considers case studies for two rivers on the Bulgarian territory using the integral method for evaluation of climatic and anthropogenic impacts on the average annual water volume and maximum and minimum water flow. The level of this impact and risk assessment is determined  by the index M i,max for the deviation of the maximum water flow from the maximum flow norm Q max,o and the index M i,min for the deviation of the minimum water flow from the minimum flow norm Q min,o . Using the dynamics of the integral indices M i,max , M i,min and information on extreme events from the past a preliminary risk assessment of future extreme events such as floods and draughts could be made. This is made for the first time in risk assessment of extreme events and has been checked at four sampling location from the National river monitoring net: Pernik and Marino pole for the Struma River catchment and Yakoruda ad Khadzhimovo for the Masta River catchment (in both cases one of the sites is at the river spring and the other near to the state border to Greece). The functions adequately describing the distribution of the frequency of  appearance of M max ,i  and M min ,i  are presented. The new approach offered includes an introduction of more specific indicators for assessing the risk of climatic impacts assessment on the river water flow (K i , M min,i and M max,i ). The period of observation is from 1948 to 2008. It has to be stressed that the indices are integral in their nature because they reflect specific climatically caused events like abundant water years, dry years, floods and droughts.