Overview of the Sonoran Desert

Where?

The Sonoran Desert stretches from the Mexican States of Baja California del Norte and the western half of Sonora to the southern third of Arizona and southeastern corner of California, covering about 120,000 square miles. [15] It includes the large US cities of Palm Springs, Phoenix, and Tucson, which are known to attract tourists during their mild winters. The orange region of the figure below define the Sonoran Desert.

Source: http://www.desertmuseum.org/desert/sonora.php

What?

The Sonoran Desert has highly variable temperatures and rainfall, typically receiving 120-300mm of precipitation per year.[16] Thus, it is lusher than most deserts, and it's mountainous terrain and proximity to the Gulf of California and Pacific Ocean creates a wide range of varying conditions. This North American Desert is a center of biodiversity, home to over 2,000 different plants species and many animals, too. [1] One of the most common plant forms of the region, the Saguaro Cactus, shown below, is unique to the Sonoran, and to many serves as a general symbol of the Sonoran Desert. Its wildflower, as shown below on the bottom, is the state flower of Arizona.

Picture Source: http://en.wikipedia.org/wiki/Saguaro

Climate Change in the Sonoran Desert

Already the hottest desert in North America, the Sonoran Desert, like the rest of the world, is facing current and future climate changes that will without a doubt have biological impacts. Significant decreases in monthly extreme minimum temperatures along with increasing average daily minimum temperatures have been seen since the 1970s and are expected to continue at even greater rates. [9] However, in a region that experiences temperatures that reach extremes below 0  degrees Celsius but maxima over 40 degrees Celsius, the number of days near extreme values, rather than the values themselves, may be of greater importance to biology.[9]

Like temperatures, precipitation levels vary greatly throughout the year. The region experiences bimodal precipitation, with rainy seasons occurring July-August and December-March. Unlike many regions of the world, the Sonoran Desert has and is expected to become increasingly drier as total annual rainfall trends show a significant negative trend.[8] The cooler rainy season, December to March, has seen a significant increase in precipitation variability over the past fifty years.[6]

The Sonoran Desert has been facing drought conditions for over a decade, which has increased the occurrence of wildfires, a historically rare phenomenon in these desert shrub lands.[9] These wildfires are most typical in the dry months of May and June before the monsoon rains hit in July. 

Figure 1 of  Abatzoglou, John T., and Crystal A. Kolden. "Climate Change in Western US Deserts"   

The figure to the right summarizes trends of two of the principle components of climate- precipitation and temperature- since 1950 along with frequency of "extreme fire danger" since 1979. [6] Note the clear increases in average minimum temperature and high variability in cool season precipitation.