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Jan Bertness

Abstract

An intensive meteorological study of summer precipitation in the Chicago area during 1976–78 furnished detailed data needed to perform a study of the impacts of rain on selected transportation-related activities and on certain utility services. Degree of effect on these activities was studied on a rain day versus non-rain day basis and further on a land use basis to help infer changes in impacts due to urban-influenced increases in rain occurrences, rainfall amounts and storm activity. Added rain resulted in over 100% more vehicle accidents, particularly in the urban area, but the accident severity associated with rain was greater in the rural areas. Rainfall decreased ridership of mass transit systems by 3–5% and apparently this was disproportionately due to midday discretionary riders such as shoppers. Little relationship of rain to pleasure boat emergencies was found but more rain decreased usage of pleasure boats. The number of delays in flight departures from O'Hare Airport was highly related to rain, increasing from only 0.3% of all flights delayed on non-rain days to 18.2&percnt delayed on heavy (≥1.3 cm) rain days. The percentage of the total electrical power outage time which was due to storms varied greatly by power district, ranging from 33% to over 80%. In general, downtown Chicago experienced less time without power due to storms, than did suburban areas. Telephone service was unaffected by rain conditions in Chicago but usage was increased. The results of these selected impacts indicate that an urban-related increase in summer rainfall will lead to certain undesirable impacts on those traveling, particularly by auto or air.

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Miren Vizcaíno
,
William H. Lipscomb
,
William J. Sacks
,
Jan H. van Angelen
,
Bert Wouters
, and
Michiel R. van den Broeke

Abstract

The modeling of the surface mass balance (SMB) of the Greenland Ice Sheet (GIS) requires high-resolution models in order to capture the observed large gradients in the steep marginal areas. Until now, global climate models have not been considered suitable to model ice sheet SMB owing to model biases and insufficient resolution. This study analyzes the GIS SMB simulated for the period 1850–2005 by the Community Earth System Model (CESM), which includes a new ice sheet component with multiple elevation classes for SMB calculations. The model is evaluated against observational data and output from the regional model Regional Atmospheric Climate Model version 2 (RACMO2). Because of a lack of major climate biases, a sophisticated calculation of snow processes (including surface albedo evolution) and an adequate downscaling technique, CESM is able to realistically simulate GIS surface climate and SMB. CESM SMB agrees reasonably well with in situ data from 475 locations (r = 0.80) and output from RACMO2 (r = 0.79). The simulated mean SMB for 1960–2005 is 359 ± 120 Gt yr−1 in the range of estimates from regional climate models. The simulated seasonal mass variability is comparable with mass observations from the Gravity Recovery and Climate Experiment (GRACE), with synchronous annual maximum (May) and minimum (August–September) and similar amplitudes of the seasonal cycle. CESM is able to simulate the bands of precipitation maxima along the southeast and northwest margins, but absolute precipitation rates are underestimated along the southeastern margin and overestimated in the high interior. The model correctly simulates the major ablation areas. Total refreezing represents 35% of the available liquid water (the sum of rain and melt).

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