1993 Flood

Hydrologic anomalies can be persistent leading to extreme regional conditions. Much has been written on the 1993 flood in the central United States. The soil was saturated at the start of the summer becasue of above normal spring precipitation. During June, several strong synoptic scale events brought continued wet conditions. During July at the center of the flooding rains, convective events occurred almost every day. This post is just a quick look at the MERRA anomalies. It is interesting to note that the magnitude of the heavy precipitation anomaly is weaker than what was observed by gage measurement (figure below). Likewise, the precipitation anomaly for 1988 (severe persistent drought) is also a smaller magnitude than observed (not shown).


The following figure shows the time series of MERRA and gage July-Aug (JJA) precipitation area averaged for the sub-basins of the Mississippi. The curious feature in this comparison is that the various sub-basins in MERRA tend to track similar to each other, or perhaps, more than the gage observations. This is apparent from the mid 1990s through the early 2000s. It seems that the spatial scale of precipitation anomalies in MERRA is larger than observed.

These features still need to be more thoroughly studied.