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National Drought Mitigation Center

NDMC News

Using CoCoRaHS observations to fine-tune drought maps

October 14, 2016

Editor’s Note: CoCoRaHS, a network of citizen scientists who report precipitation or the lack of it, was established in 1998 in Colorado and has since established a presence in every state in the country. In 2013, the Carolinas Integrated Sciences & Assessments team began cultivating a network within a network, CoCoRaHS volunteers who are specially trained to observe drought-related impacts in the Carolinas. As a result, there are more CoCoRaHS reports about drought in those states. In October 2016, working closely with the CISA team, CoCoRaHS added a scale bar to its condition monitoring reports, which most people expect will make them even more useful.

By Rebecca Ward, Extension Climatologist, State Climate Office of North Carolina

Carolinas CoCoRaHS map
CoCoRaHS reports in the Carolinas are mapped to show wet and dry values on the new scale bar. Clicking on a point takes you to the text of the report.
As a member of North Carolina’s Drought Management Advisory Council (DMAC), my role in the council’s weekly teleconferences is to give a brief overview of recent weather, namely precipitation and temperatures, and how these fit into a climatological perspective.  This includes sharing statistics, such as the temperature and precipitation rankings for individual sites across the state for various periods of time, or discussing what drought indices, such as the Standardized Precipitation Index, are indicating across the state.  In addition to these meteorological data, I also try to share recent CoCoRaHS condition monitoring reports, particularly from areas where dryness is of concern.

To understand the value these reports have, it is important to first share a bit more about the NC DMAC’s process for providing input to U.S. Drought Monitor authors.  As I mentioned, I typically begin the calls discussing recent weather and climate.  This is followed by a National Weather Service hydrologist who discusses what to expect over the coming days and weeks.  Following this is a “round-the-horn” update from the USGS about streamflow and groundwater levels across the state, reservoir level and status information from the U.S. Army Corps of Engineers, Tennessee Valley Authority, and Duke Energy, forest fire information from the NC Forest Service, and agricultural reports from the NC Cooperative Extension.  Depending on the week and how severe conditions are, other groups may also contribute information.  Following this, we take a look at the U.S. Drought Monitor author’s draft of the week’s map and discuss what the data is showing.  Then, we break out the pen (or computer mouse) and figure out where the lines delineating different categories of dryness fall based on the data.

All of this information, with the exception of the extension agent reports, is objective, and most is station-based. The extension reports provide invaluable information about agricultural conditions for the counties or districts they come from.They are the only consistent source of on-the-ground impacts information we receive, but these are only available during the growing season and not every county has a report every week.  This is where (in my opinion) CoCoRaHS condition monitoring reports can fill a gap by helping to “ground-truth” some of our indices and objective information, and by providing details about moisture and hydrology that don’t necessarily deal with agriculture.

The way these reports have been useful so far has most often been in this capacity of providing ground truth to the other data examined each week. Hypothetically, say streamflow levels are declining and we’ve seen a deficit of precipitation. Due to data sparseness, these are the only indications of abnormally dry conditions for the area of concern.  Is it time to draw D0?  Are there impacts that support this? A CoCoRaHS condition monitoring report can be that additional check mark, supporting introduction of D0 or holding off for another week.  Earlier this summer, CoCoRaHS condition monitoring reports offered that on-the-ground information, in addition to precipitation, streamflow, and county extension reports, for western NC counties when D1 conditions were being introduced.

The CoCoRaHS condition monitoring reports aren’t the whole picture, but they can help fill in some gaps, and give certainty to objective indicators.  These have become a valuable resource for information each week and I look forward to being able to use these reports in the future.  I would like to end with a thank you to the team at CISA, who have been incredibly helpful by providing information and even coming up to give a talk at our annual in-person meeting.   And I would like to give a huge, heartfelt THANK YOU to the volunteers who have taken the time to observe conditions and report on them.

For more information about CoCoRaHS condition monitoring reports anywhere in the country please visit http://cocorahs.org/Content.aspx?page=condition

For more information about CoCoRaHS condition monitoring reports in the Carolinas, please visit http://www.cisa.sc.edu/cocorahs.html

To see reports on a map showing the level on the scale bar (currently only available for the Carolinas) please visit http://www.cisa.sc.edu/map/index.html

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