Regional Climate Variaiblity and Historical Extreme Events

Partly following on to the initial evaluation of the 1993 Midwest Flooding, and also in working toward evaluation of MERRA and reanalyses for the National Climate Assessment, we have looked closer at US regional climate variability in reanalyses. While the Northwestern US summer precipitation  is handled quite well in all reanalyses (specifically NCEP CFSR and ERA Interim), owing to influence from ENSO teleconnections, the Midwestern region summer precipitation has substantial uncertainty across all reanalyses. In MERRA, for example, the interannual variance is noticeably low, so that droughts are not as dry and pluvial periods not as wet (see 1988 and 1993 respectively in the following figure).

The extreme summers of 1988 and 1993 have been tied to both large scale ENSO teleconnections and local land-atmosphere feedback processes. Given that the reanalyses data assimilation provides a strong reference for the large scale meteorology, the land atmosphere interactions would be a likely weak point in the models that may affect this uncertainty.

These results are discussed in further detail http://dx.doi.org/10.1175/JAMC-D-12-0291.1.