Coastal Impacts, Adaptation, and Vulnerabilities - Climate ...

128 Coastal Impacts, Adaptation, and VulnerabilitiesPrecipitation. Although the means of several climate model projections show anincrease in annual precipitation in the Bay, the spread is relatively wide across the models(see Figure A-1). The range in precipitation projections is likely due to the Bay’slocation; the Mid-Atlantic region is positioned between subtropical areas expected tobecome drier and higher-latitude regions expected to become wetter (Najjar et al., 2010).Although most models project these broad changes, the precise latitude that dividesareas of increasing and decreasing precipitation is uncertain.Figure A-1 Annual and seasonal temperature (top) and precipitation (bottom) changes averaged overthe Chesapeake Bay Watershed, 2070–2099. The period 1971–2000 is used as the baseline for calculatingchange. Projections correspond to the A2 emission scenario. (Source: Najjar et al., 2010, 2009).Consensus among models exists regarding precipitation increases in the winter andspring seasons. In addition, consensus exists that precipitation intensity, defined as theamount of rain falling during a season or year divided by the number of rainy days,will increase, consistent with expected changes for most of the mid- and high-latitudes(Meehl et al., 2007). Projections also suggest a greater number of droughts arising froman increase in the number of dry days and enhancement of evapotranspiration fromhigher temperatures (Hayhoe et al., 2007; Najjar et al., 2010).Sea level. Rates of local sea-level rise in the Bay in the 21st century are likely to begreater than globally-averaged sea-level rise. During the 20th century, the average rateof sea level in the Bay was 3.5 mm/yr with a range of 2.7 to 4.5 mm/yr, which was nearlydouble the globally-averaged rate (Zervas, 2001). The enhanced rate of sea-level rise inthe Bay is likely due to long-term land subsidence (Davis & Mitrovica, 1996).