We gratefully acknowledge the time and effort provided by the peer reviewers of this report: Lauren Hay, U.S. Geological Survey; and Don Wuebbles, University of Illinois.
Global climate change is already affecting average conditions in many locations around the world. Over the coming century, climate is expected to continue to change as the result of both past and future emissions of heat-trapping gases from human activities. Impacts include increasing temperatures, shifting precipitation patterns, and changes in the risk of some extreme events.
The purpose of this report is to document observed trends and projected future changes in temperature and precipitation-related climate indicators for the greater Mobile Bay area. These indicators were selected by the Gulf Coast 2 project team as being particularly relevant to analyzing the potential for climate change to have a negative impact on transportation infrastructure and operations in the Gulf Coast region. The inidcators reflect thresholds relevant to infrastructure design that can be projected using climate modeling tools and techniques. Data from five long-term weather stations in the region, Bay-Minette, Coden, Fairhope, Mobile Airport, and Robertsdale, are used in this analysis. Results from this report inform the temperature and precipitation-related analyses of the companion document, Gulf Coast Study, Phase 2: Task 2, Climate Variability and Change in Mobile, Alabama.1
Future projections are based on simulations from 10 global climate models, corresponding to three different futures: the IPCC SRES higher (A1fi), mid-high (A2), and lower (B1) emission scenarios. Statistical downscaling was performed using the Asynchronous Regional Regression Model (ARRM). Biases in simulated historical temperature and precipitation were evaluated by comparing simulated values with observations. In general, biases were larger for precipitation than for temperature, and for quantiles near the tails of the distribution as compared to the mean.
Over the past 50 years, the Mobile Bay region has experienced significant and consistent trends in fall temperatures (cooling), consecutive days per year over 95 and 100oF (increasing), summer and fall precipitation (increasing), and most quantiles of 24h, 48h, and 96h cumulative precipitation (increasing).
In the future, temperatures are projected to warm by an average of 1.5oF over the near term, 2.4-4.6oF by mid-century, and 3.2-7.7oF by end-of-century. Greater warming is projected for later summer and fall as compared to other months. Hot temperature extremes are projected to increase while cold temperature extremes are projected to decrease, with greater differences between higher vs. lower emissions scenarios for warm temperature extremes (e.g. 7-day hottest temperature) as compared to cold temperature extremes (e.g. coldest day of the year). Before the end of the century, the number of days with maximum temperature exceeding 95oF could increase by a factor of 3 under lower emissions and 10 under higher.
Little change is expected in annual average precipitation, although fall precipitation is projected to continue to increase. Nearly all precipitation extremes are projected to increase in the future, although with little difference between the values for various time periods or for higher as compared to lower emissions.
In addition to summarizing potential climate changes in the greater Mobile Bay region, this report also lays out a methodology that can be used to replicate a regional climate assessment such as this in other regions and for other climate indicators.
1 Available at: http://www.fhwa.dot.gov/hep/climate/gulf_coast_study/index.htm