Impacts of projected mid-century temperatures on thermal regimes for select specialty and fieldcrops common to the southwestern U.S.

Abstract:

The impacts of projected temperature increases in agricultural ecosystems are complex, varying
by region, cropping system, crop growth stage and humidity. We analyze the impacts of mid-
century temperature increases on crops grown in five southwestern states: Arizona, California,
New Mexico, Nevada and Utah. Here we present a spatial impact assessment of common
southwestern specialty (grapes, almonds and tomatoes) and field (alfalfa, cotton and corn)
crops. This analysis includes three main components: development of empirical temperature
thresholds for each crop, classification of predicted future climate conditions according to these
thresholds, and mapping the probable impacts of these climatic changes on each crop. We use
30m spatial resolution 2012 crop distribution and seasonal minimum and maximum
temperature normals (1970 to 2000) to define the current thermal envelopes for each crop.
These represent the temperature range for each season where 95% of each crop is presently
grown. Seasonal period change analysis of mid-century temperatures changes downscaled from
20 CMIP5 models (RCP8.5) estimate future temperatures. Change detection maps represent
areas predicted to become more or less suitable, or remain unchanged. Based upon mid-century
temperature changes, total regional suitable area declined for all crops except cotton, which
increased by 20%. For each crop there are locations which change to and from optimal thermal
envelope conditions. More than 80% of the acres currently growing tomatoes and almonds will
shift outside the present 95% thermal range. Fewer acres currently growing alfalfa (14%) and
cotton (20%) will shift outside the present 95% thermal range by midcentury. Crops outside
present thermal envelopes by midcentury may adapt, possibly aided by adaptation technologies
such as misters or shade structures, to the new temperature regime or growers may elect to
grow alternate crops better suited to future thermal envelopes.