Representing Drought Intensity in a Changing Climate with the Standardized Aridity Index (SAI)
The most direct cause of drought is a lack of precipitation, but high temperatures and low humidities exacerbate drought impacts by speeding up evapotranspiration (the amount of water that is evaporated from the landscape and transpired by plants). Droughts are becoming warmer. Understanding the effect of warmer droughts on overall drought intensity, will be valuable for local planning and to allocate drought relief assistance. The most commonly used measures of drought intensity either ignore this effect, or likely overestimate it.
The research team will improve a drought intensity measure used in many other parts of the world. They will compare how accurately the measure reflects drought-related temperature changes that affect soil moisture and crops, compared to other drought intensity measures. The revised, validated index will represent precipitation in the context of potential evapotranspiration (the demand of the atmosphere or maximum amount of water that would be evaporated or transpired if enough water were available). The team will calculate the index in real time for stakeholder feedback and will make maps of drought intensity publicly available for drought monitoring and assessment throughout the United States.
This research is part of the Fiscal Year 2026 NIDIS Coping with Drought research competition. For more information, please contact Britt Parker (britt.parker@noaa.gov).
Research Snapshot
John Nielsen-Gammon, Southern Regional Climate Center, Texas A&M University
William Baule, Texas A&M University
What to expect from this research
- The research team will produce a new standardized drought index—the Standardized Aridity Index—that is expected to better represent the sensitivity of drought to potential evapotranspiration, particularly in arid areas. They will test the drought index’s performance in a changing climate through a series of numerical experiments using hydrologic and crop models.
- The new Standardized Aridity Index will be publicly available through the Southern Regional Climate Center’s Integrated Water Portal.
- The team will also examine the impact of different definitions of drought on representations of drought severity, using indices that embody a range of sensitivities to warming temperatures. By comparing actual conditions to objective indices, local stakeholders better understand the differences between different drought definitions. These users are best able to articulate which drought definitions and approaches are most consistent with their understanding and observations of drought.
