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A B S T R A C T Stable isotope compositions of hydrogen (δ 2 H) and oxygen (δ 18 O) for short-term precipitation samples (n = 436) collected at Calgary, Alberta, Canada, between January 1997 and December 2001 were determined. Linear regression between δ 2 H and δ 18 O values of snow and large amount rain samples (≥4 mm) yielded correlation equations δ 2 H = 7.72 × δ 18 O + 5.02 and δ 2 H = 7.50 × δ 18 O + 0.27, respectively. In contrast, correlation equations between δ 2 H and δ 18 O values for small amount rain samples (<4 mm) resulted in progressively lower slope and intercept values with decreasing precipitation. Correlations of isotope data with parameters such as local temperature, relative humidity, and precipitation amount provided evidence that small amount rain samples undergo secondary evaporation accompanied by mass dependent isotope fractionation during their descent from the cloud base to the ground. Hence, the isotope compositions of precipitation at Calgary, and likely also at other locations in the North American Great Plains region, are influenced by below-cloud secondary effects. Since about one-third of the precipitation events in the 5-yr observation period were rain samples accumulating less than 4 mm, below-cloud secondary effects resulted in a slight decrease of slope and intercept values of the local meteoric water line (δ 2 H = 7.43 × δ 18 O -2.79) calculated using amount-weighted monthly average δ 2 H and δ 18 O values compared to equations based on isotope data for snow and large amount rain events only. The correlation equation (δ 2 H = 7.11 × δ 18 O -11.60) calculated using δ 2 H and δ 18 O values of individual samples (non-amount weighted) yielded the lowest slope and intercept values caused by the significant influence of small amount rain samples.

Short‐term (0.5–3 d) precipitation samples were collected from January 1992 to December 2001 in Calgary, Alberta, Canada, and the stable isotope ratios of hydrogen (2H/1H) and oxygen (18O/16O) for these samples were determined. The 10‐yr amount‐weighted average δ2H and δ18O values of precipitation were −136.1‰ and −17.9‰, respectively. Consistent with International Atomic Energy Agency (IAEA) established practice, the following local meteoric water line (LMWL) for Calgary was derived using amount‐weighted monthly average δ2H and δ18O values: δ2H = 7.68 δ18O −0.21 (r2= 0.96, n= 104). The correlation equation between δ2H and δ18O values from individual samples was found to be δ2H = 7.10 δ18O −13.64 (r2= 0.95, n= 839), which is different from the LMWL, exhibiting lower slope and intercept values. A comparison of δ2H and δ18O correlation equations with temperature during precipitation events showed a trend of decreasing slopes and intercepts with increasing temperature. Our data suggest that this is caused by incorporation of moisture derived from evaporation from water bodies and soils along the storm paths and by secondary evaporation between the cloud base and the ground during precipitation events. These processes compromise the usefulness of d‐excess values as an indicator for the meteorological conditions in the maritime source regions. The δ18O temperature dependence at Calgary was found to be ∼ 0.44‰°C−1. The study shows that short‐term sampling of individual precipitation events yields valuable information, which is not obtainable by the widely used monthly collection programs.

Acupuncture is effective for pain relief. However, the poor quality of the majority of the trials reduces the reliability of the conclusion. More high-quality RCTs are needed to verify the effects.

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