How do the heat and dryness fit into historical trends for the region?
A soon to be published report titled the "Southwest Climate Assessment" (Hoerling et al, 2012) can be used as a guide to answer these questions. Here are some findings:
Temperature and Precipitation
- The decade 2001–2010 was the warmest and the third driest in the Southwest of all decades from 1901 to 2010
- Average annual temperature increased +0.9°C +/- 0.3°C over the Southwest during 1901–2010, while annual precipitation experienced little change.
- Streamflow totals in the four major drainage basins of the Southwest were 5% to 37% lower during 2001–2010 than their average flows in the twentieth century.
- Streamflow and snowmelt in many snowmelt-fed streams of the Southwest trended towards earlier arrivals from 1950-1999, and climate science has attributed up to 60% of these trends to the influence of increasing greenhouse-gas concentrations in the atmosphere.
- The period since 1950 has been warmer in the Southwest than any comparable period in at least 600 years, based on paleoclimatic reconstructions of past temperatures.
- The most severe sustained droughts during 1901–2010 were exceeded in severity and duration by several drought events in the preceding 2000 years, based on paleoclimatic reconstructions of past droughts.
A comparison of the average 2001-2010 March/April/May (MAM) daily maximum temperature (top panel) and daily minimum temperature (middle panel). Units are °C with warmer (colder) trends shown in red (blue). Lower panel is the comparison of averaged precipitation. Units are the total change expressed as % of annual climatology, and positive (negative) trends are shown in green (orange).