The University of Arizona

Physical Characteristics | CLIMAS

Physical Characteristics


CLIMAS researchers analyzed drought patterns over time and space to better understand past events, to provide reports of current conditions, and to forecast future climate patterns for stakeholders. Analysis of historical drought included looking at instrumental atmospheric and hydrologic data from the past century in the Southwest. In addition, CLIMAS paleoclimate research provided insight into prehistoric drought occurrence by reconstructing winter precipitation for the Southwest. More frequent droughts affected different topographic areas or smaller portions of the state, so it is important to understand drought events at many scales. More frequent droughts affect different topographic areas or smaller portions of the state, so it is important to understand drought events at many scales.

Historical and current drought information synthesized by CLIMAS researchers provides part of the background necessary for drought planning. CLIMAS also provides “one stop shopping” for up-to-date climate information, including drought information, through the monthly Southwest Climate Outlook.

Research Methods

In order to provide a preliminary picture of drought variations across Arizona, CLIMAS researchers compiled and analyzed historical NOAA climate division data for the period, 1895 to 2002. Water year (October–September) precipitation data and drought indices such as the Palmer Drought Severity Index and the Standardized Precipitation Index were analyzed in order to describe drought severity and variability and their spatial patterns across the state. These data were then compared with indices that measure large-scale atmospheric circulation patterns associated with multi-year variations in Pacific Ocean circulation, such as the Southern Oscillation Index and Pacific Decadal Oscillation. These measures reflect assorted qualities of drought on varied, but overlapping, time-scales. Each portrays drought severity, duration, and extent in a slightly different way.

In addition, each month, the Southwest Climate Outlook looks at drought at the local, regional, state, and national scale in order to provide a comprehensive depiction of current and forecasted conditions. It combines climate, water resources, and fire maps and data from national and state level institutions, with news highlights, interpretation and expert assessment of these products as they pertain to Arizona and New Mexico. Graphics illustrate climate trends for the region, as well as for discrete sites, and offer another tool to resource managers and decisionmakers.


A report and drought fact sheets have been produced to aid decision makers as they prepare for drought. An initial drought assessment,“Drought and Climate in Arizona: Top Ten Questions & Answers" provides lawmakers and the public with questions and answers about major climate-related aspects of drought including history, long-term averages, seasonality, interannual and long-term spatial and temporal variability, climate extremes, and climatic forcing. For example, this study revealed that the El Niño-Southern Oscillation connection with drought is stronger in southern Arizona than elsewhere in the state. Another key finding is that year-to-year precipitation variability in Arizona was highest between around 1930-1965, and that this variability has been increasing, again, in recent years.