Oklahoma Drought

Drought

Data Limitations

Drought cannot be assessed by a single indicator. Unlike many other hazards where impacts are immediate and apparent, drought has a slow onset, sometimes goes undetected, and affects different sectors on different timescales. Consequently, it is important to assess drought using a variety of indicators, some which respond better to short-term conditions, such as for agriculture, and others that respond to longer-term conditions, such as water resources. Many indicators are combined into the weekly U.S. Drought Monitor, however, these only date back to 2000.

Definition and Description

Drought
Definition

A deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area (NWS 2009).

Description

Drought impacts vary based on the duration and intensity of the event. A few dry weeks may affect crops and lawns, while droughts lasting months or years may significantly impact large water resources. At its extreme, nearly decade-long droughts may lead to farm and business foreclosures and mass migration. Some conditions that may lead to drought development include a large-scale, stationary high-pressure system which inhibits precipitation, feedback from dry soils accelerating warming of the air, La Niña which displaces jet streams, or large-scale ocean circulations in the Pacific and Atlantic Oceans. Droughts may happen in any location and at any time of year. Impacts often become severe more quickly for drought occurring during the summer, when evaporative loss is high; however, slower-evolving droughts in the fall and winter can have tremendous economic impacts on winter crops and livestock. Droughts are more frequent in areas where annual evaporation may exceed annual precipitation.

Drought is rated by the weekly U.S. Drought Monitor (2018) on a scale from D0 (abnormally dry) to D4 (exceptional drought). D0 occurs, on average, in any given location about 21-30% of the time. D1, moderate drought, occurs on average 11-20% of the time, or roughly once every 5-10 years. D2, severe drought, occurs 6-10% of the time, or about every 10-20 years. D3, extreme drought, occurs 3-5% of the time and D4, exceptional drought, occurs 0-2% of the time, or about every 50 years. Severity is based upon a variety of drought indicators, impacts, and input from local experts.

Historical Data

U.S. Drought Risk Atlas

(Period of record varies by station; up to ~110 years)National Drought Mitigation Center

This interactive tool provides historical drought indices at a local level and can identify drought periods at different levels of severity, duration, and frequency.

1. On the left side, select Oklahoma to search by state or zoom in on the map, then search by location. 2. Scroll down to select a station from the Station List on the right or choose a station from the map. Then, click Update Selection. 3. Below, there are a variety of drought indicator tabs to explore. Choose which indicator you would like to view. 3a. The Precip & Temp tab provides weekly, monthly, or annual averages of total precipitation and minimum and maximum temperature, shown in graphs. Select a date range or select a decade or the period of record from the drop-down menu. Select weekly, monthly, or annual information from the Aggregate drop-down menu. 3b. The Drought Monitor tab shows values from the U.S. Drought Monitor, which began in 2000. Select a date range and a Boundary (state, county, etc.). There are three ways to view the information. Select Time Series to view a graph of U.S. Drought Monitor values over time, averaged over the boundary you selected, Table to view a table of weekly drought monitor values, or Heat Map to view weekly values by year (use the slider to scroll through the weeks). 3c. The Trends tab shows various trends in several drought indicators and how statistically significant those trends are. Under the Index drop-down menu, select precipitation or a drought indicator. For any indicator, select a Start Year and Significance level. Some indicators require you to also select a Season, and the Precipitation indicator requires a Precipitation Threshold in inches. After you make the selections, click Trends Chart on the right. A graph will display with the trend in the selected indicator over time. A blue dashed trendline represents an increasing trend in that indicator, a red dashed trendline represents a decreasing trend, and a black dashed trendline represents no trend. The trend value per decade is shown in text underneath the graph.

Historical Climate Trends Tool

(1895-present) Southern Climate Impacts Planning Program

This interactive graphing tool shows precipitation trends, of which very dry periods are a drought indicator. It can also be used to help estimate the probability of future precipitation and hence drought events.

1. On the left side column (moving from top to bottom) choose OklahomaClimate Division of InterestSeason of InterestPrecipitation. 2. Hovering the curser over a point will display the year and total rainfall for the selected season. 3. For more information on how to interpret the chart, click on Chart Info on the bottom left.

U.S. Drought Monitor Time Series

(2000-present)National Drought Mitigation Center

This interactive graphing tool shows the frequency of drought conditions since 2000, along with each drought’s maximum intensity and duration (shown by color scale). The U.S. Drought Monitor is the official source for aid decisions by the USDA and several other agencies and programs.

1. In the top banner, next to Area Type choose either Climate Division or County 2. Next to Area, either type in OK to select climate division of interest or type in county of interest. 3. Next to Index, select USDM. 4. Zoom in by clicking inside graph and dragging over a specific time-period.

National Water Information System Tool

(Period of record varies by station; up to ~70 years) U.S. Geological Survey

This interactive tool displays recent and historical reservoir storage and streamflow, along with water quality and meteorological parameters. If correlated to periods of drought, this tool can be used to show the impacts of drought on water resources which can affect drinking and irrigation water supplies.

1. Select a county from the list. 2. Under Water Level/Flow Parameters, select Reservoir storage and/or Streamflow. 3. Under Choose Output Format, scroll down to Retrieve data for. Select the option for the date range: and enter your desired dates. Some stations go back as far as 1950. If you select this year, the graph will display all available data. 4. Under Output Options, select Graphs of data with long-term statistics to display the data in a graph. 5. Click Submit. 6. The results page includes graphs of all stations in the county.

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