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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

  • 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.

Paleoclimate Context

  • 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.

Observed Temperature/Precipitation Trends - 1901-2010

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).