Building accurate historic and future climate MEPDG input files for Louisiana DOTD : tech summary.

SIO No. 30000425 / LTRC Project No. 12-2P
The new pavement design process (originally MEPDG, then DARWin-ME, and now Pavement ME Design) requires two types
of inputs to infl uence the prediction of pavement distress for a selected set of pavement materials and structure. One input is
traffi c, more specifi cally, truck axle loadings. The other input is climate, a multi-year set of hourly data including temperature
precipitation, wind speed, humidity, and percent sunshine. The climate data is then transformed into temperature gradients that
infl uence pavement material properties. For this study, the term MEPDG is used and refers to all of the software versions and name
changes.
When the MEPDG was initially launched in 2007, the climate fi les were generally 5-10 years of data, some were incomplete records
(gaps in the continuous hourly data), and files started with climate data in the 1990s. As the MEPDG developed, more data was
added to many files and incomplete files were corrected or omitted. The most common geographic locations of MEPDG climate
data files are associated with regional and large airports. Although there were 11 files, the distribution of the files across the state
was limited. A pavement analysis would require the use of a climate record that may not be near the project location and would
require the same climate data to be repeated to complete a 20- to 40-year pavement distress prediction period.
This study applies climate science to improve the depth and length of climate data so the
pavement engineer can apply the best climate input data when examining a pavement design.
There is a deeper body of climate history and significantly more climate stations to draw from.
The climatologist can assemble longer, higher quality climate history files and convert those files
using global climate models into data representing a predicted future climate.
The objective of this study was to apply the best available climate science to build climate input
files for use in the MEPDG. The objective was expanded to consider the naturally occurring
cycles in climate temperature and precipitation.
The first step was to generate a historic climate file for each parish in Louisiana and assemble
the climate data in electronic format required for input into MEPDG model. By building a climate
file for each parish, a pavement designer can simply select the climate file for the parish where a
project is located. The appropriate historic length of time for these data was established as 1970
through 2009. Every parish does not have a site with an observational record for that period, so
an interpolation method in space and time was used to fill in data gaps.
The Automated Surface Observation System (ASOS) and the Cooperative Observer Program
(COOP) were two sources used to generate historical climate fi les. For the 40-year time
period and types of data needed for this study, these are the only two sources of data archives
available.