Complexity of solar variability, hydrology and climatic conditions as evidenced in the case of the Oulujoki and Kemijoki river basins, Northern Finland

Abstract

The work concentrates on the dependency relations between the sunspot numbers, mean annual temperatures, annual precipitation rates, mean annual discharges (MQ), mean discharges of the flood months and coinci­dent monthly mean temperatures and winter precipitation figures on the basis of general trends, correlation coefficients and regression analysis results. All the dependency relations are examined using absolute values, and the first five also by reference to 5‑year moving means. With the excep­tion of a few individual items, the information on the Oulujoki river basin reached as far back as 1896 and that on the Kemijoki river area to 1911. Attention was paid to the years before regulation of the flow of these rivers as well as to the whole observation period up to 1980 both when determining the correlation coefficients and in the regression analysis, where the dis­charge rates were the dependent variables and other factors, individually and in varying combinations the independent variables.

Even though in the preliminary comparison the 11‑year sunspot maxima seemed almost regularly to follow an exceptionally low discharge and vice versa, sunspots could not explain more than approx. 10 % of the changes in terms of absolute values. The situation altered completely upon transformation of the data to moving means, the explanatory power reaching 38.3 % at best, while in the case of the other factors the opposite trend was observed in the corresponding situation. This was taken as evidence of the fact that changes in sunspot numbers are revealed in meteorological and hydrological changes more distinctly over periods of more than one year, whereas, from the negative correlation between sunspot numbers and precipitation rates, attention was directed to a possible relation between solar and cyclonic activity. The various combinations of factors chosen to explain the hydrological changes reached an explanatory power of approx. 50 % at most.