Vol. 37, No. 2, Fall/Winter 1999- "Weather and Climates in Pennsylvania"
CLIMATE CHANGE AND WATER RESOURCES OF THE DELAWARE RIVER BASIN
(pp. 3 - 19)
Jay W. Hodny
W. L. Gore & Associates, Inc.
John R. Mather
Department of Geography
University of Delaware
Newark, Delaware
Abstract
Increasing water demands, coupled with a finite water supply, provide the potential for water shortages in the Delaware Rive Basin due to changes in the region's climate. The Thornthwaite-Mather water budget is used to study potential changes in water resources in response to possible future climatic changes. Two different General Circulation Models (GCMs) are used to examine the response of water budget variables to changes in temperature and precipitation. The changes in temperature and precipitation when going from a simulated 1xCO2atmospheric concentration to a simulated 2xCO2atmosphere are applied to a current climatic data set and interpolated to 29 0.5° of latitude by 0.5° of longitude grid points covering the study region. The Thornthwaite-Mather water budget is evaluated at each grid point for both GCM data sets. Evaluation of data developed by two different GCMs over the Delaware River Basin shows only minor changes in temperature (an increase) and precipitation (a decrease) in going from current to hypothetical 2xCO2conditions. The hydroclimate of the area should experience warmer and dryer conditions with less surplus of water, a decrease in streamflow, as well as an increase in water deficit conditions, and a marked decrease in snow accumulation. Use of the GCM temperature and precipitation data in a climatic water budget approach permits 3 The Pennsylvania Geographer — Volume XXXVII No. 2 — Fall/Winter 1999 quantitative evaluation of the future hydroclimatology of an area under conditions of changing CO2conditions.
A HYDROCLIMATIC APPROACH TO ASSESSING WILDFIRE RISK IN PENNSYLVANIA
(pp. 20 - 42)
Petra A. Zimmermann
Center for Climatic Research
University of Delaware
Newark, Delaware
Abstract
A climate-based approach is employed to assess wildfire risk in a two-county region in Pennsylvania. A generalized ground cover is applied to Schuylkill and Carbon counties and the duff moisture content within it is computed using a method based on the Thornthwaite-Mather water budget. Water budget computations are performed for Tamaqua, PA, and are used to investigate the feasibility of using a single station for the study area. Daily duff moisture data are then compared with daily fire to examine the relationships between wildfire occurrence and the moisture state of the duff. This analysis is conducted for the years 1981 to 1984 and 1988 to 1991. Results show that drier duff conditions are associated with increased numbers of mean fires per day, increased fire-day ratios, and greater numbers of fires per fire day. These relationships are evident when the study period is examined as a whole. Deviations from these established relationships are seen when individual study years are analyzed. This is likely due to the anthropogenic nature of wildfires in Pennsylvania. Overall, the Thornthwaite-Mather water budget does designate dry and possibly dangerous conditions quite satisfactorily.
SIGNIFICANT TORNADO ACTIVITY IN SOUTHWESTERN PENNSYLVANIA
(pp. 43 - 63)
William Monfredo
Department of Geography
Southwest Texas State University
San Marcos, Texas
Abstract
Although strong and violent tornado frequency is relatively low in Pennsylvania compared to the central United States, tornado activity can be a hazard to persons living in the Keystone state. Pennsylvania possess a higher incidence of significant tornado activity than many other populated areas of the United States; significant tornadoes, rated F-2 to F-5 on the Fujita damage scale, occur in the region with occasionally tragic results. This paper explains tornadoes, reporting biases, and conditions suitable for the occurrence of tornadoes in southwestern PA. Tornado activity from 1880 to 1995 was examined to find monthly frequencies and F-scale distributions, times of occurrence, total path lengths, mean widths, mean lengths, and deaths and injuries for three categories of southwestern PA significant tornadoes: all, deadly, and non-deadly. Data analysis shows that significant tornadoes in the fifteen-county southwestern PA area are most likely during the late afternoon and early evening in late spring and early summer, particularly June, but can occur anytime from early spring through late fall. On average, deadly significant tornadoes are more than three times as long as their non-deadly counterparts and are nearly twice as wide. Without proper public awareness and emergency planning, the results of future significant tornadoes in this populated area could prove just as disastrous as in 1944 and 1985.
TEMPORAL TRENDS IN MEAN TEMPERATURE AND HEATING AND COOLING DEGREE-DAYS ACROSS PENNSYLVANIA
(pp. 64 - 79)
Robert V. Rohli
Department of Geography and Anthropology
Louisiana State University
Baton Rouge, Louisiana
Abstract
Temporal trends in annual mean temperature, seasonal heating degree-days (HDDs) and cooling degree-days (CDDs), and monthly values of these variables are examined for eight stations across Pennsylvania during the 1948-1995 period Some linear trends in the temperature and degree-day variables that suggest long term warming are identified, particularly in the stations located on coastal or lake plains (namely Philadelphia, Willow Grove, and Erie). Parabolic trends that suggest initial cooling and subsequent warming are identified at a few sites, particularly Pittsburgh and, to a lesser extent, Williamsport. These linear and parabolic trends seem to be dominated by changes in spring and summer. Few significant linear or non-linear trends are detected at Allentown, Harrisburg, or Wilkes-Barre/Scranton. Relationships of these temperature variables to changes in local sulfur dioxide emissions should be examined more closely, particularly in the industrial (or formerly industrial) cities in steep, local valleys.
A CLIMATOLOGICAL SUMMARY OF PENNSYLVANIA'S STATE SYSTEM OF HIGHER EDUCATION UNIVERSITIES
(pp. 80 - 101)
Diane Stanitski-Martin
Kay R. S. Williams
Department of Geography-Earth Science
Shippensburg University
Shippensburg, Pennsylvania
Abstract
This research compares and contrasts the climatic regimes of the fourteen universities in Pennsylvania's State System of Higher Education (SSHE), 1961- 1990. The locations of the schools represent four of the six climatic divisions within Pennsylvania. The difference in climate across Pennsylvania is influenced by its mid-latitude location, proximity to the Great Lakes and the Atlantic Ocean, and its changing topography. The presented graphs illustrate the state's variable temperature, precipitation, and snowfall. Data show that mean monthly temperatures were highest in California, Millersville, and West Chester, which represent stations with low latitude and elevation. Lowest mean monthly temperatures were found in Edinboro, Mansfield and Slippery Rock, stations with the highest elevations and latitudes. Average monthly precipitation tends to be highest during July at all locations except for Mansfield, which experiences a June maximum. Edinboro receives an anomalous amount of snow due to lake effects, enhanced by its high elevation.
LINEAR AND NONLINEAR RELATIONSHIPS BETWEEN THE PNA, NAO AND WINTERTIME PENNSYLVANIA CLIMATE
(pp. 102 - 124)
Brent Frakes
Department of Geography
Southern Illinois University
Abstract
The North Atlantic Oscillation and Pacific/North American teleconnection patterns have been shown to exhibit an influence over Pennsylvania temperature and precipitation. In this study, the affect of these patterns is analyzed for each winter month at the climate division resolution for the years 1950-1999. The NAO shows the strongest linear association with temperature, especially in December. The PNA pattern is the main control of precipitation variability during all months and is strongest in February. Both patterns exhibit a degree of nonlinearity, although relationships are space and time specific, and is often related to the position of the Appalachian Mountains. The role both teleconnection patterns have over Pennsylvania's climate has changed drastically throughout the 50-year period. During the 1960s and 1970s, almost half of the temperature was explained by each of the patterns although the strength of the associations has declined in recent decades. Understanding the roles the NAO and PNA have on Pennsylvania's climate will not only help in forecasting, but should contribute to understanding how the state's climate has varied and changed.
THE IMPACT (?) OF EL NIÑO ON PENNSYLVANIA PRECIPITATION
(pp. 125 - 140)
Anthony J. Vega
Anthropology, Geography and Earth Science Department
Clarion University
Clarion, Pennsylvania
Abstract
Due to the significance of recent El Niño/La Niña events, there has been much speculation as to the impact of these events on the climate of the Northeast US, especially Pennsylvania. This is especially true concerning precipitation as the greatest documented El Niño influence is on polar jet stream variations. As the jet forces virtually all cool season and much of warm season precipitation in the state, speculation centers on the role of El Niño events on the precipitation climatology of the state. This study identified trends in both statewide and intrastate regional precipitation. Precipitation has significantly increased in the state over the past century with the western areas of the state experiencing the greatest increases. These increases have been limited to the winter and spring seasons which fuels conjecture concerning possible El Niño forcing. However, such conjecture is unfounded as no relationships were found between El Niño and Pennsylvania precipitation on any temporal or spatial scale.
LIGHTNING DAMAGE IN PENNSYLVANIA: 1959-1998
(pp. 141 - 158)
Gregory E. Faiers
Department of Geography
University of Pittsburgh at Johnstown
Johnstown, Pennsylvania
Abstract
A recent study found that lightning causes more damage in Pennsylvania than in any other state in the United States. This statistic seems unusual because many Southern states have two or three times as many days with thunderstorms as does Pennsylvania. While there have been national studies conducted to reach such conclusions, there has been no detailed analysis of the impacts of lightning within the borders of Pennsylvania. The purpose of this research, therefore, is to evaluate the geographic patterns of lightning impacts across the state in order to gain a better understanding of how and why lightning is such a hazard within Pennsylvania. It was found that while thunderstorms are most frequent in the southwestern part of the state, the greatest number of damaging strikes occurs in the southeastern corner of Pennsylvania where the greatest populations are. Statistically, the number of damaging strikes and total damage per county was significantly associated in a positive manner with county population and per capita income and insignificantly (and slightly negatively) associated with average number of thunderstorm days. Not surprisingly, Philadelphia and Allegheny Counties reported the greatest total dollar losses, but Lancaster and Chester Counties reported more damaging strikes and had more significant departures from what would be expected based on their populations and per capita incomes.
DIGGING THEMSELVES A HOLE: DREDGING AND THE CHANGING VALUE OF WESTERN PENNSYLVANIA'S RIVERS
(pp. 159 - 194)
David L. Prytherch
Department of Geography and Regional Development
The University of Arizona
Tucson, Arizona
Abstract
This paper briefly traces the history -- natural and social -- of the commercial dredging of sand and gravel resources in western Pennsylvania. The environmental issues that have arisen in recent years from this activity are examined within the context of expanding knowledge of aquatic ecosystems and changing resource valuations in Pennsylvania. Changes in environmental policy, where dredging is no longer viewed as a public service, but perhaps as a destructive use of public resources, provide an analytical lens for understanding the changing way western Pennsylvanians have viewed their rivers.