Drought turning into water.

Is Your Area Really in a Drought? The Truth About Weather Patterns and Water Availability

Jordan Keane monogram
Jordan Keane in Climate & Environment August 2026 • 4 min read.

"Understanding the link between meteorological and hydrological drought indices to better assess water resources in your community."


Droughts are a recurring challenge in the United States, significantly impacting communities and natural resources. While many people rely on general drought indicators, understanding the nuances of these measurements is crucial. It ensures that communities can accurately assess their water resources.

Most drought monitoring systems base their findings on meteorological data, primarily precipitation levels. However, droughts have far-reaching consequences that extend to other aspects of the water cycle, like streamflow. Relying solely on precipitation can paint an incomplete picture, as the relationship between rainfall and actual water availability is complex and varies from region to region.

A recent study examines the connection between various drought measurements and streamflow. The study highlights how climate, geographic characteristics, and human activities affect this relationship. By understanding these factors, communities can improve their drought monitoring and implement effective water management strategies.

AI Search Multiple angles on this topic

Drought Data Infrastructure

The United States has developed extensive infrastructure for monitoring hydrologic drought conditions. The U.S. Geological Survey maintains benchmark datasets and simulation results for hydrologic drought events across the conterminous United States. Drought.gov operates an operational version of the Climate Engine API, producing hundreds of drought indices daily based on multiple foundational datasets. The National Weather Service's Climate Prediction Center converts temperature and precipitation outlooks into projected Palmer Hydrological Drought Index values for future months.

Drought Analysis Methods

Hydrological drought is commonly characterized by indices such as the Standardized Streamflow Index (SSI), which is widely used for its straightforward formulation and calculation. A multidisciplinary review identifies five primary drought analysis methods: index-based, remote sensing, threshold-level, impact-based, and the storyline approach. The threshold level method derives drought characteristics including duration and deficit volume. Single low flow indices, such as percentiles from the flow duration curve, are also commonly used. However, there remains limited understanding of what the SSI actually captures about hydrological drought conditions.

Historical Drought Monitoring

The Palmer Drought Severity Index (PDSI) has been used to map drought conditions in the contiguous U.S. from January 1900 onward. The Palmer Hydrological Drought Index (PHDI) is a long-standing metric that measures hydrologic impacts and responds more slowly to changing conditions than the PDSI. The National Centers for Environmental Information provides monthly maps of drought conditions as measured by multiple Palmer indices. Historical data and conditions help communities better understand and prepare for drought and extreme weather threats.

How Do Meteorological and Hydrological Drought Indices Differ?

Drought turning into water.

Meteorological drought indices typically use precipitation as the primary indicator. The Standardized Precipitation Index (SPI) is a common example. These indices are useful for understanding rainfall deficits, but may not reflect the complete picture of water availability.

Hydrological drought indices, on the other hand, consider factors such as streamflow, reservoir levels, and groundwater. These indices provide a more direct assessment of water resources available for human use and ecosystem health. However, streamflow can be influenced by many factors besides precipitation.

  • Climate and Catchment Properties: Local climate patterns, soil types, and vegetation affect how precipitation translates into streamflow.
  • Human Influences: Dams, reservoirs, and water diversions alter natural flow patterns, complicating the relationship between rainfall and streamflow.
AI Search Multiple angles on this topic

Advances in Drought Characterization

Recent global research highlights the limitations and sectoral biases of single-index drought analyses, though they remain widely used. A novel Composite Drought Index (CDI) is designed to capture agricultural, hydrological, meteorological, and socioeconomic components on a seasonal time scale. Researchers have produced a new geodetic drought index (GDI) using GPS data to characterize hydrologic drought conditions in surface and sub-surface hydrologic reservoirs. An innovative hybrid data-driven model integrates geomorphological, hydrological, and human activities factors to predict hydrological drought indices.

Challenges in Drought Definition

Numerous indices exist for the definition and description of hydrological drought, which refers primarily to streamflow drought. These indices have been developed for various purposes including planning of water resources and flow allocations, analysis of temporal trends, and assessment of climate change influence. The proliferation of different drought definitions and indices creates challenges for consistent monitoring and comparison across regions. Different indices may yield conflicting assessments of drought conditions in the same area.

Drought Index Comparison

Different drought indices measure different aspects of drought conditions and may not always agree on the severity or spatial extent of drought events. The choice of drought index can significantly affect the assessment of drought conditions in a given area. No single index captures all dimensions of drought, which is why researchers increasingly recommend using multiple indices for comprehensive drought assessment.

To get a clearer idea, it is important to look at different meteorological drought indices, those that include evaporation or snowmelt. Evaporation, especially in dry climates, affects the amount of water available. Snow processes in colder climates contribute to spring and summer streamflow. Understanding the local environment helps figure out which indexes will be more effective.

What Does This Mean for Drought Monitoring?

Communities need to consider more than just precipitation when assessing drought conditions. Streamflow data, while valuable, must be interpreted carefully. In areas with significant human modifications to water systems, streamflow may not accurately reflect the natural water supply. Using a combination of different indicators and understanding local factors helps to improve drought preparedness and water resource management.

AI Search Multiple angles on this topic

Drought Recovery Analysis

The National Centers for Environmental Information provides estimations of drought recovery in the Contiguous U.S. based on Palmer drought analysis. These projections use varying scenarios to estimate how drought conditions may improve over time. Drought termination and amelioration are complex processes that depend on multiple factors including precipitation patterns and initial soil moisture conditions.

Future Drought Projections

Future projections from global climate models indicate increasing trends in drought frequency and intensity for many areas of the world by the end of the century. The United States Drought Monitor serves as initial conditions for the Climate Prediction Center's drought outlooks. Researchers critically discuss future drought projections, focusing on key issues related to the concept of drought and its frequent confusion with aridity. Downscaled CMIP6 models provide global future drought layers showing projected changes in drought conditions.

Integrated Drought Management

Existing gaps exist in the sustainable management of drought, particularly regarding Hydrological Ecosystem Services (HES). Integrating physical and socioeconomic indicators is proposed for assessing drought impacts. In regions where ground data are scarce, hydrological modeling offers an alternative approach for drought monitoring and developing early warning systems. The SWAT model combined with drought indices provides a systematic framework for watershed-scale drought assessment.

Human Dimensions of Drought

Drought impacts extend beyond environmental and hydrological systems to affect human communities and socioeconomic systems. The way people perceive and respond to drought conditions is influenced by both scientific data and local knowledge. Understanding drought requires integrating technical monitoring with the lived experiences of communities affected by water scarcity.

About this Article -

Written with AI assistance from published research, and reviewed by the Mystum team. See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1029/2017wr022412, Alternate LINK

Title: Natural And Human Influences On The Link Between Meteorological And Hydrological Drought Indices For A Large Set Of Catchments In The Contiguous United States

Subject: Water Science and Technology

Journal: Water Resources Research

Publisher: American Geophysical Union (AGU)

Authors: E. Tijdeman, L. J. Barker, M. D. Svoboda, K. Stahl

Published: 2018-09-01

Everything You Need To Know

1

What distinguishes meteorological drought indices from hydrological drought indices in assessing drought conditions?

Meteorological drought indices, like the Standardized Precipitation Index (SPI), primarily use precipitation data to identify rainfall deficits. However, they may not fully represent overall water availability. Hydrological drought indices focus on streamflow, reservoir levels, and groundwater, offering a direct assessment of water resources for human use and ecosystem health. The difference lies in what they measure: rainfall versus actual water in rivers and reservoirs.

2

Why is it insufficient to depend solely on precipitation measurements when monitoring drought conditions?

When monitoring drought, communities shouldn't rely solely on precipitation data. Streamflow data is valuable, but its interpretation needs careful consideration, especially in areas with human-modified water systems. A combination of meteorological drought indices and hydrological drought indices, along with an understanding of local factors like climate, catchment properties, and human influences, is crucial for improving drought preparedness and water resource management.

3

How do climate, catchment properties, and human activities complicate the relationship between precipitation and streamflow in drought monitoring?

Climate patterns influence how precipitation translates into streamflow through factors like temperature and evaporation rates. Catchment properties, like soil type and vegetation, determine how much water is absorbed or runs off into streams. Human influences, such as dams, reservoirs, and water diversions, alter natural flow patterns, affecting the relationship between rainfall and streamflow. Failing to consider these elements can lead to inaccurate drought assessments.

4

What specific types of drought indices should be considered to assess the impact of evaporation or snowmelt on water availability, and why are they important?

To assess evaporation or snowmelt, several drought indices are used. For evaporation, indices might incorporate temperature and humidity data to estimate evaporative demand. For snowmelt, indices consider snowpack depth, snow water equivalent, and temperature to predict the timing and volume of snowmelt runoff. By using these indices, one can get a more complete picture of water availability beyond just rainfall.

5

What are the potential drawbacks of relying exclusively on precipitation data, such as data used in the Standardized Precipitation Index (SPI), to evaluate drought severity and its implications for communities?

Using only precipitation data, like with the Standardized Precipitation Index (SPI), offers an incomplete view of water availability because it does not account for factors influencing the water cycle, such as evaporation, snowmelt, or streamflow. This may lead to inaccurate assessments of water resources. Communities would benefit by integrating hydrological drought indices that consider streamflow, reservoir levels, and groundwater, alongside meteorological drought indices for a complete overview of drought conditions.

Newsletter Subscribe

Subscribe to get the latest articles and insights directly in your inbox.