A non-global warming explanation for the lack of moisture/drought in the US Southwest deals with the lack of Hurricane activity in the Eastern Pacific basin. The moisture, upper-level outflow, and accentuation of the monsoon can all be traced back partially to EPAC storms, which are highly sensitive to SST conditions in the equatorial Pacific (ENSO). Simple reanalysis calculations for inactive minus active EPAC seasons shows very significant deficits of monthly mean cloud water, precipitable water, and surface specific humidity (among a host of other variables) for Aug-Sept months over the US Southwest.
This image is constructed as follows: I take the Accumulated Cyclone Energy over the Easter Pacific TC basin for the months of July – September (Oct is usually quiet). I calculate the seasonal deviations from the 1979-2007 mean EPAC ACE — which is fairly bimodal — as one would expect with the sensitivity to ENSO. I then take the active and inactive years (0.5 sigma) and composite the August & September column cloud water (or any other variable) differences (date obtained here from Japanese Reanalysis Project; one could use NCAR/NCEP or ERA40). So, I have 10 years of active and 9 years of inactive ACE years in the EPAC. The following example shows that a greater than 20% difference in cloud water is associated with whatever is concomitant with active vs. inactive EPAC hurricane seasons. This means that a researcher or a responsible journalist would ask: what weather patterns or climate regimes are typically associated with decreased rainfall in the Southwest US, which is a desert, if anyone cared to notice? Instead you get hyperbolic, speculative propaganda about an “upcoming century of fires”.
Despite what Harry Reid says and no matter how hard CNN pushes the Planet in Peril to link global warming to these fires (also NBC, CBS, ABC and the rest of the so-called mainstream media), it is partially the lack of hurricanes that has contributed to the excessive drought conditions — talk about an inconvenient truth. And, by the way, the Northern Hemisphere Tropical Cyclone activity is still on pace to be the weakest since 1977 — Tropical Activity