An Analysis Of Climate Trends In The Susquehanna River Basin . - Ship
An analysis of climate trendsin the Susquehanna Riverbasin, PennsylvaniaKatherine Smith
Table Of ContentsAbstract . 1Introduction . 2Purpose & Scope . 3Literature Review. 3What is Global Warming . 3Trends in Climate over Time . 6Impacts of Global Warming . 7Climate Trends and Impacts within Pennsylvania . 10Climate Change Analysis . 11Methods for Analyzing Climate Change . 13Diurnal Temperature Range . 13Precipitation . 14Streamflow . 16Study Area . 18Methods . 20Diurnal Temperature Range . 23Precipitation . 24Hydrology . 25Graphic Representation . 27Results. 27Maximum Temperatures – 1895 to Present . 27Maximum Temperatures – 1980 to Present . 29Minimum Temperatures – 1895 to Present . 29Minimum Temperatures – 1980 to Present . 31Diurnal Temperature Range – 1895 to Present. 31Diurnal Temperature Range – 1980 to Present. 33Precipitation – 1895 to Present . 33Precipitation – 1980 to Present . 35Comparative Analysis with Elevation, Latitude and Longitude . 35Streamflow . 38Conclusions . 38References . 43
List of FiguresFigure 1 . 2Figure 2 . 19Figure 3 . 20Figure 4 . 26Figure 5 . 28Figure 6 . 28Figure 7 . 30Figure 8 . 30Figure 9 . 32Figure 10 . 32Figure 11 . 34Figure 12 . 34Figure 13 . 39List of TablesTable 1 . 19Table 2 . 19Table 3 . 22Table 4 . 22Table 5 . 38
AbstractLong term climate analyses have shown an increase in globalatmospheric carbon dioxide levels since the Industrial Revolution. Thisincrease in carbon dioxide not only increases temperatures but also acceleratesthe hydrologic cycle. Within the last century, global average temperatures haveincreased by nearly 1 C; a majority of this increase seen in the last 50 years.The impacts vary, but can include an earlier timing of spring, extended growingseasons, and shifts in water supplies. The Susquehanna River basin providesapproximately 50% of the fresh water for the Chesapeake Bay. Any projectedchange in climate within the watershed has the potential to influenceagricultural and recreational activities in the basin, as well as influencechanges in an already stressed Chesapeake Bay. Five aspects of the basin’sclimate were analyzed over two time periods for their trend slope values usingFORTRAN programming; the results were then spatially represented utilizing aGIS. Results have found that maximum and minimum temperatures are risingfor both time periods. Increases in maximum temperatures are greater thanminimum temperatures, and temperature increases from 1980 – 2008 aregreater than those seen from 1895 – 2008. As a consequence of the changes inmaximum and minimum temperatures, diurnal temperature ranges areincreasing when looking at the 1895 – 2008 period of record, but aredecreasing when looking at 1980 – 2008. Precipitation indicates largeincreases over both periods of time studied. Streamflow indicates an overallincrease in drainage, with the exception of spring.Page 1
IntroductionOver the last century, Earth’s climate has been changing due toanthropogenic actions (IPCC 2007). Precipitation events have become moreerratic, while temperatures across the globe have increased. The subsequentimpacts of global warming are already being felt. Many climate analyses havebeen conducted for the Earth as a whole, its continents, and various countries.Recent climate studies are being performed at finer scales, such as the stateand watershed. This project will analyze any changes in climate that haveoccurred in the Susquehanna River basin (Figure 1) over the period of record(1895 – 2008).Figure 1: The Susquehanna River basin in relation to the Chesapeake Baywatershed.Page 2
Purpose and ScopeIt is important to understand current regional trends in climate given thevariable nature of climate and the uncertainty that potential future changescan bring to a region. This study will focus on the Susquehanna River basinand analyze climate trends across the basin over the period of record (1895 –2008). The Susquehanna River basin is home to nearly 4 million people, andits water uses include not only domestic, but also agricultural and industrial.Specific aspects to be looked and questions to be asked include: How has the seasonal and annual diurnal temperature range changedover time? How have the seasonal and annual maximum and minimumtemperatures changed over time? How has seasonal and annual precipitation changed over time? How has seasonal and annual streamflow changed over time? What are the spatial patterns of the above temporal trends throughoutthe basin?Analysis of these trends and their spatial patterns will lead to a betterunderstanding of climate variability within the basin.Literature ReviewWhat is Global Warming?Page 3
The greenhouse effect is essential to life on Earth. Greenhouse gases(water vapor, carbon dioxide, methane, nitrous oxide, and ground level ozone)exist naturally within the atmosphere (IPCC 2007; Miller 2008). These gasestrap outgoing terrestrial radiation, which in turn warms the surface of theEarth through reradiation (Miller 2008). Long term climate analyses show thatrecent changes in average climate are due to increases in carbon dioxide levelswithin the atmosphere since the Industrial Revolution (Bell and others 2004). A70% increase in anthropogenic greenhouse gas emissions has occurredbetween 1970 and 2004 alone (IPCC 2007, Miller 2008).Earth responds to this increase in the atmosphere’s capability to trapmore radiation by adjusting the energy balance so a new equilibrium is reached(Miller 2008). Changes in the mean, or average, climate have profound impactson the intensity and frequency of extreme climatic events (Bell and others2004). The distribution of most precipitation and temperature events follow anormal curve. Small changes in the mean temperature, for example, have thepotential to shift the normal curve resulting in large changes of eventfrequency. This creates an effect of increasing future extreme events at oneend (maximum temperatures) while decreasing the opposite extremes(minimum temperatures) (Meehl and others 2000; Unkašević and others 2006).Detecting, and attempting to predict, future temperature change is often whatdrives climate change analysis (Boyles and Raman 2003).Page 4
The simple act of measuring temperature can complicate climateanalysis. In the United States, historical temperature records are collected bythe National Weather Service’s Cooperative Station Network, which relies onvolunteers to record the maximum and minimum temperatures as well asprecipitation once within a 24-hour “observational day.” This day is defined bythe convenience of the volunteer. If temperature readings happen to be takenat different times of the days, error and bias are then introduced into the dailytemperature statistics. Monthly maximum and minimum temperatures areespecially vulnerable to this error (Janis 2002).Temperature is not the only variable that is going to change as theclimate changes. As temperature increases, the amount of latent heatincreases the atmosphere’s capacity to hold moisture, creating a positivefeedback. Subsequently, the hydrologic cycle is intensified and acceleratedthrough increasing amounts of evaporation and transpiration. In somelocations, this can create more frequent precipitation events (Hergel and others2004, Arnell 1999).This positive feedback amplifies the human – induced warming that isalready taking place due to increased carbon dioxide levels. It is thought thatan accelerated hydrologic cycle may be enough to double the effect seenthrough current increases in carbon dioxide alone (Miller 2008). On the otherhand, accelerating the hydrologic cycle also creates a change in the amount ofcloud cover. The increased cloud cover then has a net cooling effect byreflecting more incoming solar radiation. There is still insufficient evidence toPage 5
determine the exact impact of increased cloud cover on global temperatures(Miller 2008).Trends in ClimateCurrent changes to the mean climate have already been recorded. Therehas been an increase in the global mean temperature over the last century ofapproximately 0.74 C (Miller 2008). The linear trend for temperatures withinthe 50 years spanning from 1956 to 2005 are nearly twice the trends of the 100years that span from 1906 to 2005 (IPCC 2007). Moreover, of the twelvehottest years on record since 1850, eleven of them occurred between 1995 and2006 (IPCC 2007; Miller 2008). If these changes were due to naturalvariability, the observed trends for air temperature would be similar topredicted values including only natural variability. This is not the case. Theincrease can be connected to human – induced climate change since observedair temperature is significantly different than estimates that only includenatural variability (Hergel and others 2004).As the mean temperature continues to rise at locations across the globe,an increase in the number of extreme hot days and a decrease in the numberof extreme cold days have been observed (Meehl and others 2000). If thischange was due to a shift in the normal distribution of daily observations, thenthe increasing trend for both cold and warm extremes would be equal.However, there have been more increases in the cold extremes than for warmextremes across the globe. Cold temperatures have shown a stronger increasePage 6
in the Northern Hemisphere than the Southern Hemisphere (Hegerl and others2004). This is more than likely due to the Northern Hemisphere having moreland coverage and a higher human population concentration than theSouthern Hemisphere, and therefore, the effects of human – induced warmingis greater. The potential for a warmer climate in the future may lead to longergrowing seasons, with hot days becoming a frequent part of prolonged heatwaves. A decrease in the number of cold days leads to a decrease in thenumber of frost days (Bell and others 2004).On the other hand, since 1900, precipitation has declined within theMediterranean, southern Africa, and portions of southern Asia. Increases inprecipitation have also been seen in northern Europe, northern and centralAsia, and the eastern portions of North and South America (IPCC 2007; Miller2008). The intensity and frequency of extreme precipitation has also increasedacross the globe (IPCC 2007). This change is due to storms being able to carrymore moisture (Miller 2008).Impacts of Global WarmingMany of the future impacts of global warming are unavoidable, makingadaptation crucial (UCS 2008). Recent rises in global temperatures willcontinue to affect changes in the timing of spring events, including leaf –unfolding, as well as shifts in plant and animal species distribution. Currently,agriculture is affected by earlier spring crop plantings, while forests have toPage 7
adapt due to fire and an increase in pests within the higher latitudes of theNorthern Hemisphere (IPCC 2007).If global average temperatures increase by 1.5 C – 2.5 C, there is a 50%to 80% confidence level that around 20 – 30% of currently known plant andanimal species are at an increased risk for extinction. If temperatures exceedthat range, significant changes within the structure and function of ecosystemswould occur. This would result in negative effects on food and water supplies(IPCC 2007).Food production in the mid– to high– latitudes, and overall globally, islikely to increase with a rise in temperature that ranges from 1 C – 3 C.Depending on the region, some areas can expect an increase in precipitationfed crops by approximately 5 – 20%. However, this is not the case for everyregion. Lower latitudes have the potential for decreases in productivity withtemperature increases (IPCC 2007). Crops that are currently within the warmextent of their suitable range are extremely susceptible, especially those thatrely heavily on various water resources. Such crops include cotton, rice, corn,apples, peppers, potatoes, and watermelons (Draper and Kundell 2007; IPCC2007).Accompanying the increase in temperatures, the current projections forprecipitation show a 5% increase in the global land average by the end of thecentury. How climate change will affect regional precipitation is still unclear,even more so than with temperature changes (Miller 2008). Changes inPage 8
temperature and precipitation will naturally lead to changes in runoff, andsubsequently in most areas, water supplies and resources.Runoff is projected to increase by 10 – 40% in mid– to high– latitudes bythe middle of the 21st century (IPCC 2007; Miller 2008). Runoff changes wouldlead to changes in reservoir storage amounts and timing of releases. Manyareas that rely on reservoir storage, like the Southwestern United States, arealready trying to handle the growing demands and associated competitions forscarce water resource supplies (Miller 2008). This combined with currentprojections of earlier snowpack melts and resultant reductions in summerstream flows would increase competition over already sparse water resources(IPCC 2007).Aside from climate variability, water availability is also dependent onnumerous factors, including changes in: population growth, populationconcentration, industrial use, agricultural use (irrigation), water use (includingefficiency and management of demands), as well as current environmentalrequirements (Arnell 1999). All of these can vary at any given time, makingestimates of the future water use difficult. Future assessments are madebased on assumptions of potential changes within different areas (Arnell 1999).Within North American metropolitan areas, intense heat waves arealready occurring. These heat waves are projected to increase in intensity,frequency, and duration (IPCC 2007). Warming within western North Americais expected to decrease snowpacks, increase winter flooding, and reducePage 9
summer streamflow. This portion of North America will endure harsher effectsof climate change compared to eastern North America (IPCC 2007).Climate Trends and Impacts within PennsylvaniaPennsylvania encompasses 76% of the Susquehanna River basin (SRBC2008). Within Pennsylvania alone, annual temperatures have been rising (USC2008). Two of the most notable trends are that winter has warmed the most ofall the seasons, and many cities have experienced an increase in the number ofsummer days over 32 C (UCS 2008). In the northeast region of the state,changes in the timing of leaf buds as well as insect migration show indicationsof the earlier arrival of spring. All of these changes currently being observedare related to human – accelerated climate change (IPCC 2007; UCS 2008).Annual precipitation has increased approximately 5 – 20% statewide,with the exception of south – central Pennsylvania. Since 1970 alone, therehas been an increase in the precipitation that is seen during winter, spring andfall. Winter snowcover has been decreasing steadily across the state, with afaster paced decline within the last few decades. Summer is the only seasonthat has had slightly less rainfall (UCS 2008).Specific to Pennsylvania, a dramatic increase in the number of summerdays over 32 C is expected throughout the state, subsequently increasing thenumber of heat waves. This will cause urban air quality to decline and putvulnerable populations at risk to heat – related health issues, as well asintensify asthma and other respiratory diseases (UCS 2008). Increases inPage 10
temperatures will stress agriculture. Dairy cattle are thought to reduce milkproduction as temperatures rise. Crop yields of grapes, sweet corn, andvarious apple varieties could decline due to an increase in the presence of pests(UCS 2008). A reduction in winter snow packs is expected, along with adecline in snowmobiling. Ski resorts could remain in operation until about themiddle of the century, when temperatures rise too high to sustain evenartificial snow (UCS 2008). It is expected that there will be a shift in plantspecies such that warmer weather species will become more abundant inPennsylvania; one example is poison ivy.Climate Change AnalysisTraditional climate analysis is generally done at specific locations byanalyzing data that are available over the period of record. Trends intemperature and precipitation from one location can then be easily comparedto another location (Boyles and Raman 2003). Generally, researchers useobservations from one location as indicators for a large surrounding area, if theregion has relatively homogeneous vegetation and topography (Pielke andothers 2000). However, the results at a single location do not necessarily applyto what is happening throughout a larger region (Boyles and Raman 2003), andcalculating a regional average based on a single point location can bemisleading (Pielke and others 2000).Local climate analysis can help to precisely reflect the complex climatethat exists. It can also offer a more comprehensive understanding of thePage 11
different patterns occurring within temperature and precipitation data (Boylesand Raman 2003). If local temperature variability increases, the result will belarger temperature increases than what is anticipated for the future (Hegerland others 2004). In order for there to be effective response and mitigation toglobal climate change, local level assessment on the potential changes needs tobe conducted. Since local level climate changes are uncertain at a fine scale,they cannot be satisfactorily represented through global climate models (Belland others 2004). Instead, analyzing a location’s climate trends is what iscustomarily used to define the local climate (Boyles and Raman 2003).Although various models and equations have been used to assess climatechange impacts at the local level, a major complication that arises is whetheror not the region can accurately be represented within those models.Downscaling, or using regional variables to help define a local climate within aglobal climate model, is a method that has been frequently used (Dibike andCoulibaly 2005; Giorgi 2008; Hayhoe and others 2007; Mareuil and others2007). However, the ability to accurately downscale predictor variables, suchas precipitation, still needs to be fully assessed with an emphasis on extensivemodel experiments (Dibike and Coulibaly, 2005; Mareuil and others 2007).A more simplistic approach is to analyze the spatial and temporal trendscurrently taking place. Linear trends have the ability to be easily compared tochanges not only throughout different regional locations, but also acrossvarious time periods (Boyles and Raman 2003). Spatial analysis also helps toPage 12
alleviate the issue of inferring regional climate trends through a single site(Pielke and others 2000).Methods for Analyzing Climate ChangeDiurnal Temperature RangeDiurnal temperature ranges (or DTRs) are the mathematical differencebetween the daily maximum and minimum temperatures. The DTR is oftenused in climate studies since the use of mean temperature alone can hide verysignificant temperature change patterns by averaging the trends (Boyles andRaman 2003; Holder and others 2006). There are also dramatic variationswithin daily and weekly trends, along with seasonal variances (Boyles andRaman 2003; Durre and Wallace 2001; Holder and others 2006). It is rare thatobservations will follow a smooth trend over a significant period of time (Holderand others 2006).It has also been concluded that for most regions, the DTR will decreaseas mean temperatures increase (Boyles and Raman 2003; Bell and others2004). This will occur when the increase in minimum temperatures is greaterthan the increase in maximum temperatures (Bell and others 2004). Aspreviously stated, a shift in the mean temperature causes changes in thefrequency of events. The same can be said for the DTR. Any adjustment in themean temperature could induce large changes for the DTR (Unkašević andothers 2006).Page 13
Prior studies of the DTR have found that there is variance across thecontiguous United States throughout different geographic regions (Durre andWallace 2001). One study has modeled the sensitivity of carbon dioxide withinthe atmosphere and addressed the timing and length of the growing season inrelation to the DTR (Bell and others 2004). A study in North Carolina hasfocused on separating seasons based on the astronomical definitions, January– March categorized as winter, April – June categorized as spring, and so on,and found the same trend of a decreasing DTR (Boyles and Raman 2003).In North Carolina, studies have shown that minimum temperatures haveincreased over time, with the most noticeable increases in the summer and thefall, while overall maximum temperatures have increased just slightly (Boylesand Raman 2003). This change in summer minimum temperatures alters theDTR, creating a much narrower range. Prior studies in the Susquehanna Riverbasin specific to annual temperature alone utilized data from Philadelphia, PAand New Haven, CT. The study found that annual average temperatures since1781 have remained near the long term average of 8.8 C. There have beenthree cooling periods throughout this record; however, recent annualtemperatures have risen to the warmest levels on record (Leathers and others2008).PrecipitationAlthough global average precipitation is projected to increase,precipitation changes will likely not be consistent across the globe in bothPage 14
location and timing. Precipitation is dependent on numerous factors including,but not limited to: season, temperature, and topography. An understanding ofprecipitation patterns is important to governments and industries across theglobe (Boyles and Raman 2003). The reliability by which global climate modelscreate daily precipitation estimates at fine scales is not clear, especially whenprecipitation is due to a convective event (Mareuil and others 2007).Numerous studies indicate that extreme precipitation events will becomemore frequent (Boyles and Raman, 2004; Mareuil and others 2007; Miller2008). Precipitation is likely to become more intense daily, which is wellrecognized as an effect of anthropogenic warming (Gutowski and others 2007).Some predictions indicate that there will be the greatest increase in extremeprecipitation events where greater than two inches fall within a 24 – hourperiod (UCS 2008).With the exception of the southwestern United States, most of the UnitedStates is projected to become wetter (Miller 2008). Previous studies of thenortheast United States indicate that annual precipitation has been increasingover the last century, with decadal increases specific to the spring, summerand fall, and decadal decreases in the winter (Hayhoe and others 2007).Within North Carolina, throughout most of the state, fall and winter hadincreased precipitation, summer had decreased precipitation, and spring hadno overall trend throughout the state (Boyles and Raman, 2003). Prior studiesthat utilized proxy data within New Haven, CT and Philadelphia, PA determinedPage 15
that the Susquehanna River basin had an overall increase in the amount ofannual precipitation since 1829 (Leathers and others 2008). These twolocations were used since there is no data for the Susquehanna River basinthat dates back to the early 1800’s.StreamflowSince global climate change and the water cycle are so intricately linked,it is important to consider other portions of the hydrologic cycle than justprecipitation. Along with precipitation, runoff is expected to change as aresponse to climate change. Precipitation change is a crucial component forchanges in runoff, but evaporation changes are equally important since it iscontrolled by changes within temperature and humidity (Miller 2008). Soilmoisture will change as a response to changes in precipitation as well. Forexample, if soil moisture is low, the amount of runoff will be low as well due toincreased infiltration during precipitation events.Predictions for changes within runoff indicate an increase for the easternportion of North America (Miller 2008). The demands for water are alreadyhigh since it is essential to every aspect of the way we live our lives. Not only dohumans rely on water for our own economic growth and food production, butevery level along the food chain requires water (Draper and Kundell 2007;Miller 2008). Demands for water on a global scale have increased due to risingpopulations, while our global supply of water has remained constant.Page 16
By improving the ability to manage effects of current hydrologicalimpacts such as droughts and floods, future changes may be able to be bettermanaged as well (Miller 2008). In order to do this, we need to have a betterunderstanding of the past and current hydrology within a region. Since therecord only extends for a finite interval, it is not an accurate representative ofhydrologic cycles, both wet and dry. Of more concern within the historicalrecord are manmade structures that have been put in place to manage thehydrologic flow conditions (Draper and Kundell 2007).Previous studies have found that with increases in regionaltemperatures, snowmelt will accelerate and result in an earlier runoff.Changes in the resultant flood magnitudes will depend on the combined effectof changes within the precipitation amounts and the timing of the midwinter tospring thaw (Mareuil and others 2007). In some portions of the world, theearlier timing of the spring stream flow will cause problems in the summerwhen the peak agriculture demand occurs (Draper and Kundell 2007).Other studies have found that significant increases in runoff could resultin increases of a return period of specific floods (Mareuli and others 2007).Within the Susquehanna River basin, reconstructed and historic dischargeacross the basin fluctuates. Most notable are different trends including dryperiods (1730s, 1840s, 1960s), as well as shorter moist periods (1810s, 1830s,and 1970s) (Leathers and other
The Susquehanna River basin provides approximately 50% of the fresh water for the Chesapeake Bay. Any projected change in climate within the watershed has the potential to influence agricultural and recreational activities in the basin, as well as influence changes in an already stressed Chesapeake Bay. Five aspects of the basin's
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