DWR Drought Image

Contoured baseflow (circles) and well (triangles) percentile data. Current or selected month ranked against data from same month in previous years (1965 - 2023). Graphic re-drawn each Tuesday.

D4 Exceptional	D3 Extreme	D2 Severe	D1 Moderate	D0 Abnormally Dry
< 2	2 - 5	5 - 10	10 - 20	20 - 30

Normal	Wet
30 - 70	> 70

Contoured baseflow percentile data. Current or selected month ranked against data from same month in previous years (1965 - 2023). Graphic re-drawn each Tuesday.

Contoured well percentile data. Current or selected month ranked against data from same month in previous years (1965 - 2023). Graphic re-drawn each Tuesday.

Today: July 3, 2024
The DWR Drought Image brings together two data sources: groundwater levels from the Drought Indicator Wells network and surface water gage data. The daily surface water gage data is filtered to create a daily baseflow data set. Date of interest values are ranked against the historical baseflow data and the resulting percentiles are contoured. Similarly, groundwater levels from the date of interest are ranked against the historical groundwater level data and those percentiles are contoured. These graphics are shown in the middle and bottom maps, respectively. Percentile rankings from both data sets are combined and contoured in the top map.

Because groundwater level data begins in 1965, USGS gage data from 1965 or later for a selection of North Carolina gages are filtered using a technique known as the Lyne and Hollick algorithm. The resulting baseflow values are stored and used to compare to current values. Each baseflow value approximates the daily amount of discharge occurring into a gaged stream from the subsurface.

The USGS gage data and a portion of the well data are collected using satellite telemetry, so daily values are available each day. DWR has added cell phone telemetry to 17 wells and is planning on adding telemetry to the remainder of the drought indicator wells they monitor as time and funds allow to improve the resolution of this picture of the natural subsurface storage conditions. If the latest groundwater level data point ages beyond 30 days old, it is dropped from the data set that is contoured. So, adding more telemetry sites will improve the drought depiction. Drought Management Advisory Council (DMAC) contour intervals and colored fills are used to help the end user compare this image to the national drought illustration.

DWR hopes that DMAC members will use these graphics to help form their recommendations to the US Drought Monitor.

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Arnold, J.G., P.M. Allen, R. Muttiah, and G. Bernhardt. 1995. Automated baseflow separation and recession analysis techniques. Ground Water 33(6): 1010-1018.

Arnold, J.G. and P.M. Allen. 1999. Automated methods for estimating baseflow and groundwater recharge from streamflow records. Journal of the American Water Resources Association 35(2): 411-424.

Nathan, R. J. and T. A. McMahon. 1990. Evaluation of automated techniques for base flow and recession analyses, Water Resour. Res., 26(7). 1465-1473.

Lyne, V., and M. Hollick. 1979. Stochastic time-variable rainfall-runoff modelling, Hydrology and Water Resources Symposium, Institution of Engineers Australia, Perth, 89-92.

DWR's baseflow calculations make use of FORTRAN source code and explanatory information from Texas A&M University and USDA.

The DWR Drought Image is created using the Generic Mapping Tools system.