Drought indices are based primarily on rainfall deficits over varying periods of time. The Lawn and Garden Index indicates deficits or surpluses over a three-week period versus the amount typically needed (about 1 inch per week) and is calculated daily. The Crop Moisture Index, calculated weekly, adds the factors of temperature and evaporation to rainfall amounts to describe soil moisture conditions and has a time horizon of about 4 to 8 weeks. The Palmer Drought Severity Index moves the horizon back to effects felt over several months so as to provide information about hydrologic systems such as streams and rivers. Because of this longer time frame and its associated hydrologic inertia, the PDSI changes little from week to week while the LGI and CMI might change dramatically depending on weekly rainfall. These indices are natural indices as they are unaffected by the management of surface and ground water. Gardeners and landscapers use the LGI and it is also a leading indicator of potential drought. Agricultural interests are the prime users of the CMI as their business decisions are based on soil moisture availability. Water system managers (municipal, utility etc.) look to all of these indices as the requirements of their customers generally vary considerably.
Integrated measures of drought are found in the river gage, reservoir level and ground water level measurements reflecting not only past climatic conditions of the basins but of the management decisions of the hydrologic systems in those basins. There may be high variability in these measurements from week to week and basin to basin because their values depend not only on rainfall, but on management decisions.
Lawn and Garden Index - Provided by Alabama Office of the State Climatologist
Crop Moisture Index - Developed by Climate Prediction Center, NWS, provided by AOSC
Palmer Drought Severity Index - Provided by the Climate Prediction Center, NOAA
Streamflow Level Percentiles - Provided by USGS
Please review the Draft Drought Plan and submit comments and suggestions to:
Office of Water Resources
Alabama Department of Economic and Community Affairs
P.O. Box 5690
Montgomery, AL 36103-5690
Voice: (334) 242-5499 Fax: (334) 242-0776
drought@adeca.alabama.gov