RIVER RUNOFF EXTREMES AND TENDENCIES:
FACTORS OF RISK LIKELY RELATED TO GLOBAL CLIMATE
G. PÁNDI., J. MIKA.
ABSTRACT. - River Runoff Extremes And Tendencies:Factors Of Risk Likely Related To Global Climate. River runoff data are analysed at different sub-catchments in the Transylvanian Basin of the Carpathian Mountains. Spatial and temporal variability, as a source of hydrological risk, are first quantified for the 19 gauging stations. Temporal variability of decadal time-scales are statistically related to the hemisferical warning trend (0.26 K/decade) observed in the 1974-1998 period. Method of instrumental variables is used to estimate linear regression coefficients between regional rainfall and hemispherical mean temperature for this period. The sequence of consecutive years is defined for instrumental variable, that fulfil the main criterion i.e. the non-zero correlation to the independent variable (r=0.825). Regression analysis is also performed for parallel 9 precipitation stations for independent validation, and for the monthly absolute extremes of the 25 years. Another validation of the terults applies independent hydrological parameters in Hungary. Both spatial and temporal variability are about one decimal magnitude, that makes existence of continuous observations rather important. Trends of the runoff are mainly decreasing parallel to the global warming-up tendency of the investigated 25 years. For 0.5 K hemisferical warming the local order of runoff changes spreads from several percents to tens of percents. The largest area-mean decrease of runoff is analysed for the July-August period, with average decrease of 75 %. Although there are two further independent estimations in the study, that support the discovered relation between drying-out of the Basin and the warming tendency of the Hemisphere, this relation of the robust part of the runoff sample may not be extended to the tails of the distribution.