Twentieth century variability of surface humidity as the climate change indicator in Krakw (Southern Poland)

Air humidity is an element that plays an important role among meteorological processes within the atmosphere; however, the variety of humidity indices makes the global view of air moisture changes difficult. Long-term variability of air humidity in Krakw was examined by time-series (1901-2000) analysis of vapour pressure and saturation deficit values and their characteristic days with the background of temperature and saturated vapour pressure changes. Long-term variability of air humidity in Krakw has been visible above all in variations of saturation deficit. It should be connected with the contemporary temperature growth and the city development as the atmospheric water vapour content (described by vapour pressure) becomes relatively stable (with no significant tendencies). The parameter showed well-marked trends over the examined period. The growth of saturation deficit values predominated in the warm half of a year (above all in August: an increase in SD value by 3.0 hPa per century). Apart from atmospheric circulation variability, gradual rise in the number of inhabitants and higher development density contributed to the decline in the city's air humidity; however, the causes of changes in air humidity should be also attributed to natural factors, mainly to variation of air circulation reinforced by the operation of anthropogenic factors. Using air humidity as the indicator, the results that confirm climatic fluctuations in central Europe in the twentieth century obtained earlier were verified and some new aspects of present climate change were given.