Drought Conditions Can Exist, Even with Rain
Published: Friday, April 4, 2025
The following is from Beth Hall, Indiana State climatologist.
If one looks at the latest U.S. Drought Monitor map for Indiana, one might scratch their head—particularly as it has been raining recently. Well, drought is a tricky thing.
Critically, there are several types of drought. Meteorological drought tends to only focus on how much precipitation has fallen and how that amount compares to historical totals for that same period. Since drought tends to consider periods of time from 30 days to several consecutive months, recent heavy rains —while likely above normal compared to that same period, historically—may not be enough to ignore the longer-termed deficits of the recent 30, 60, or 90 days.
Figure 2 illustrates how the total precipitation from since' Feb. 24 and Jan. 24 through March 25 compared to historical amounts over that same period. The maps indicate where there are warmer colors (e.g., orange) total precipitation is still below normal through parts of central and southwestern Indiana.
Another type of drought is hydrological. This focuses on impacts from precipitation deficits on water systems such as groundwater, lake and pond levels, and streamflows. Some of these can respond quickly to rainfall events (e.g., streamflows), others may take longer to recover (e.g., groundwater).
Additionally, hydrological indicators may not be co-located with where the rain fell. In other words, while sufficient rain may have fallen locally, streams and groundwater that have water sources elsewhere may be significantly below normal due to a lack of precipitation elsewhere. This may result in local impacts, particularly if the streams and groundwater are a critical water source to the local environment.
The last type of drought (for this article) is agricultural drought. This type can usually respond rather quickly when precipitation is abundant. Indicators can be visible stress on crops and dry soil moisture. At this time of year, there is not a lot of crop vegetation to assess drought intensity. Soil moisture monitoring from the Purdue Mesonet suggest most soils across the state are plenty moist from 2 inches down to 20 inches. However, modeled soil moisture products from the National Oceanic and Atmospheric Administration indicate soils across central Indiana, when averaged over a longer period, are drier than normal.
Ultimately, the U.S. Drought Monitor considers a wide range of indicators and products. Additionally, they invite input from state drought task teams to inform them of what the local community is seeing in addition to observational data. The Indiana State Climate Office leads this effort in Indiana along with participation from a wide range of programs such as the Indiana Department of Natural Resources, Indiana Departments of Emergency Management and Homeland Security, U.S. Department of Agriculture, National Weather Service and Purdue University Extension.
The national U.S. Drought Monitor author has the final say in what the weekly map will look like. Hopefully, this helps explain why the weekly map might seem to contradict what outside conditions may look like. Period of consideration (last 30 days to 4-6 months), types of drought to consider, and the wide range of indicators must all be captured in this single product.
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