Data on hydrometeorological conditions and E. coli concentration were simultaneously collected on 57 occasions during the summer of 2000 at 63rd Street Beach, Chicago, Illinois. The data were used to identify and calibrate a statistical regression model aimed at predicting when the bacterial concentration of the beach water was above or below the level considered safe for full body contact. A wide range of hydrological, meteorological, and water quality variables were evaluated as possible predictive variables. These included wind speed and direction, incoming solar radiation (insolation), various time frames of rainfall, air temperature, lake stage and wave height, and water temperature, specific conductance, dissolved oxygen, pH, and turbidity. The best-fit model combined real-time measurements of wind direction and speed (onshore component of resultant wind vector), rainfall, insolation, lake stage, water temperature and turbidity to predict the geometric mean E. coli concentration in the swimming zone of the beach. The model, which contained both additive and multiplicative (interaction) terms, accounted for 71% of the observed variability in the log E. coli concentrations. A comparison between model predictions of when the beach should be closed and when the actual bacterial concentrations were above or below the 235 cfu 100 ml(-1) threshold value, indicated that the model accurately predicted openings versus closures 88% of the time.

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Field studies in the Colorado Front Range provide data for calibrating and testing a model that computes incoming longwave radiation in alpine terrain. The model estimates longwave irradiance on the basis of empirical terrain and atmospheric radiance distributions. A statistical analysis of estimated versus observed longwave irradiance indicates no difference between the regression line and a line of one‐to‐one correspondence. Simulations of longwave irradiance to cirque floors within the study area reveal subtle variations that are due to differences in ground slope and the configuration of surrounding ridges. The simulated variations in longwave irradiance are not adequately represented by the commonly employed istoropic approximation. Surrounding rockwalls enhance the energy balance of alpine snowfields by reducing their net longwave loss circa 50% below that of an unobstructed ridge top. The added energy is equivalent to roughly 0.5 m of melt when integrated over an entire snowmelt season.