| A 10-year (1992--2001) record of stable isotope compositions of hydrogen and oxygen for precipitation at Calgary, Alberta, Canada was obtained. The precipitation samples were collected during short periods rather than monthly collection, which is the standard practice of the Global Network of Isotopes in Precipitation (GNIP). It was shown that isotopic records of short-term precipitation provide unique information on the occurrence and the extent of secondary evaporation between cloud base and ground, and evapotranspiration over the continents, two processes in the atmospheric water cycle that are difficult to ascertain by other scientific methods.; 10-year amount-weighted average delta2H and delta 18O values of Calgary precipitation were -136.1‰ and -17.9‰. The local meteoric water line for precipitation at Calgary based on amount-weighted monthly mean delta2H and delta180 values was delta2H = 7.73delta18O + 0.10.; For small (<5 mm) rain samples, the slope of the linear correlation equation between delta2H and delta18O values was less than 7, indicating significant secondary evaporation between cloud base and ground. In contrast, the slope of the linear correlation equation between delta2H and delta18O values for snow and large rain samples was 7.7, indicating no or little secondary evaporation between cloud base and ground.; Back-tracking storm trajectory techniques reveal that the delta 2H-delta18O correlation equation for continental polar (cP) airmass-origin samples was delta2H = 7.96delta 18O + 6.45, whereas the corresponding equation for maritime pacific (mP) airmass-origin condensate samples had slopes between 7.65 and 7.82 and intercept values ranging from 4.01‰ to 8.22‰. The lower slope was attributed to evapotranspiration.; The delta2H and delta18O signals for condensate samples were incorporated into a modified Rayleigh fractionation model to determine the contributions of moisture from continental evaporation (by d-excess values) and transpiration (by delta2H-T and delta 18O-T correlations). Model calculations suggested that in the years between 1997 and 2001, evaporation over the continent was not a major contributor of moisture for Calgary precipitation events. In contrast, transpiration on the continent played an important role in providing moisture for Calgary precipitation (average transpiration contribution exceeded 50%), according to the model calculations. |
