What is the purpose of this tool?
Just how dry (or wet) have recent weather conditions been where I live? This question highlights the primary purpose of the SCIPP drought tool, which is to compare current or recent conditions in precipitation with conditions experienced over the last hundred years or more. Human memory more often than not causes us to overestimate the magnitude of recent events, causing us to think things such as “this has to be the wettest month we’ve ever had” or “the last few months are the driest I’ve ever seen,” when in reality conditions may have been similar to conditions normally experienced during that time. While periods of unusually and sometimes exceptionally dry or wet weather certainly occur, the most dependable way to put recent conditions in context is to compare current data with past data.
The drought tool looks at precipitation conditions experienced across a specific period of time as selected by the user (either 30 days, 60 days, 90 days, 180 days, or 365 days) and compares this period with long-term meteorological records which typically date back more than one hundred years. These comparisons are not made at individual points, but rather across climate divisions which are regions within a state that experience very similar temperature and precipitation conditions. The end product of the tool is a table of information comparing the selected period to all the past conditions.
This tool has been developed to provide real-time monitoring of rainfall and drought conditions over different windows of time (30, 60, 90, 120, 180, and 365 days). In general, the tool is intended for any user who has a need to, responsibility for, or interest in monitoring precipitation and related drought conditions. This includes – but is not limited to – individuals in agriculture, professional drought monitoring, local and regional-level water management, local government, and others needing such information for decision-making. We encourage anyone interested in the tool to check it out and provide any feedback you may have. Feedback can be provided to us by posting a message here.
The drought tool is an interactive application that allows you to browse through information as displayed in a dynamic table. The tool consists of a main table on the right portion of the display accompanied by a title describing the table contents. Below the table there is a dynamic map displaying one piece of the information from the table. On the left-side portion of the display there are a series of tabs which can be used to browse a different state, view a different time in the calendar, map a different layer of information, and change the period of interest. As items are clicked in the left-side tabs, the data will automatically update in the table and accompanying map to the right.
To start using the tool, first select your state of interest from the State tab on the left side (note: this experimental tool is only available for states in the south and southeast U.S.). Next, select the Time Period – that is, the number of days you would like to use for the comparison (either 30, 60, 90, 180, or 365 days). After you select a period, you can also easily select a different time period to see how the numbers in the table change. If you happen to have an interest in conditions not from present date but instead, last month, or perhaps a previous season, this can be accomplished by clicking on the Date tab at the left and changing the calendar date (note: the date tool is limited to going back 4 months from the current date). The information that results now is based off the date and time period you selected. The last item in the tabs on the left is the Map Layers tab, which adjusts the information provided in the map below the table. There are 4 items to choose from including Rainfall Total (second column in the table), Departure From Normal (third column in the table), % of Normal (fourth column in the table), and SPI which stands for the Standard Precipitation Index (tenth column in the table).
The data in the table are also sortable by column. To sort the data by column click on the up/down arrow to the right of the title in the particular column you would like to sort by. Clicking once will sort the data in ascending order, clicking a second time will sort the data in descending order. If you would like to return the table to its original state, sort the first column (Climate Division) in ascending order.
The accompanying map below the table is also dynamic and uses the Google Maps interface. You can pan the map by clicking on the image and holding your mouse button down (left button on a PC mouse, any button on a mac mouse) while moving the mouse as desired. The map can also be navigated using the buttons at the top left part of the map. The directional arrows move the map in the directions shown while the plus zooms in and minus zooms out. Information pertaining to the climate division numbers and names can be obtained by clicking on the map.
Detailed descriptions of each column of information are available in the table by clicking the column title. The following are brief summaries of each:
Climate Division: Regions of a state that experience very similar temperature and precipitation conditions over the course of time. While climate conditions contribute to today’s climate divisions, historically the divisions were based purely on county boundaries, river basins, and agricultural areas. Each division contains a series of historical meteorological sites available for computing long-term trends and comparisons with observations made today.The number of climate divisions varies by state depending on the climate diversity. Within the Southern Climate Impacts Planning Program (SCIPP) region, states have the following number of climate divisions: Oklahoma (9), Texas (10), Arkansas (9), Louisiana (9), Tennessee (4), and Mississippi (10).
DFN: DFN stands for the departure from normal and is the difference between observed rainfall and the 30-year average rainfall for a particular period. A positive DFN means that precipitation has been above normal while a negative DFN indicates a precipitation deficit. The 30-year averages are updated every ten years for each climate division and are currently based on the 1971-2000 precipitation values.
Percentage of Normal: Observed rainfall divided by the average rainfall (which is then multiplied by one hundred). This value is an indicator of precipitation surplus or deficit for a given period of time where a value greater than 100% indicates a surplus and a value less than 100% indicates a deficit. For instance, a value of 200% would indicate that precipitation in a climate division has been twice the average value for the period which represents a substantial surplus.
Driest Since: This column shows the last period in which precipitation totals were less than or equal to recent conditions. Also shown in this column is the observed precipitation that occurred during that period.
Wettest Since: This column shows the last period in which precipitation totals were at least as much as recent conditions. Also shown in this column is the observed precipitation that occurred during that period.
Driest Rank: This number is a ranking of the current period as compared to conditions observed in all past periods in the climate division’s history. For instance, if the driest rank was “10/100” for the 30-day period ending on March 30, 2010 for a particular climate division, this means that March 1-30, 2010 was drier than 90 other March 1-30 periods. It also tells us that only 9 other periods were drier, meaning that from a historical perspective, recent conditions were significantly dry.
Driest on Record: This number displays the driest period in the historical record for the given time period of interest. Included here is the lowest rainfall total for the period as well as the year(s) in which it occurred.
Wettest on Record: This number displays the wettest period in the historical record for the given time period of interest. Included here is the highest rainfall total for the period as well as the year(s) in which it occurred.
SPI: SPI stands for the Standardized Precipitation Index (SPI) and is a drought index based only on precipitation. The SPI can be used to monitor conditions on a variety of timescales which allows the SPI to be useful in both short-term agricultural and long-term hydrologic applications. The SPI value represents an estimation of the unusualness of a precipitation total, based on the climate division’s history. Larger absolute values (both above and below zero) represent increasingly unusual events. Values of -1 and lower indicate dry conditions while values greater than 1 indicate wet conditions. The table available here contains information on SPI values and how it relates to dry and wet conditions. This index was developed in 1993 by T. B. McKee, N. J. Doesken, and J. Kleist.
This column displays the SPI value for the specified period of time as well as associated drought values (ranging from D0 to D4) when dry conditions exist. The drought values are not the official designations provided by the National Drought Mitigation Center and merely serve as one indicator of conditions. Drought experts at the National Drought Mitigation Center take not only the SPI but many other indicators into account when providing their official drought designations which come out each week on Thursday.
Similar Season In Last 30 yrs (Score): The similar season is a past period whose precipitation conditions most closely resemble the period of interest. This takes into account the total precipitation that occurred, the character of the precipitation (for example, was rainfall due to a couple major events or many smaller precipitation events?), and the timing of precipitation. Information in this column includes the closest matching period as well as a score that rates the level of the match (ranging from 0 to 10 with 10 being a perfect match). The comparison years have been limited to the past 30 years to support recollection of these past events. For more details of the algorithms used to calculate the similar season and score, please visit the following page).
Who developed the drought tool?
This tool is an experimental product developed by the Southern Regional Climate Center (SRCC) and Southern Climate Impacts Planning Program (SCIPP) Regional Integrated Sciences and Assessment (RISA) program. The product is based largely on concepts originally developed by researchers at the Oklahoma Climatological Survey.
Why is the tool only available across the South and Southeastern United States?
The initial version of the experimental drought tool is intended for testing purposes only. The region of focus has been limited to the SCIPP region plus points east and south which comprises the southeastern corner of the nation. From a climatological standpoint, this region experiences the most significant geographic change in average rainfall (outside of topographical effects) observed across the United States. This hydrologic diversity thus makes it an appropriate region in which to test the tool. Through continued testing and feedback within this defined region the tool will be modified in support of future expansion to other parts of the country.
Where can I provide feedback?
If you have any feedback or comments to provide regarding the Southern U.S. Drought Tool, please contact us by posting a message here. Thank you for your time and interest in this experimental tool!