Drought turning into water.

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

Jordan Keane in Climate & Environment August 2025 • 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.

How Do Meteorological and Hydrological Drought Indices Differ?

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.

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.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.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

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.

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.

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.

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.

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.