With this tool, you can compare changes in monthly, seasonal, and annual variability of parameters such as temperature, precipitation, and a variety of drought indices. (ncdc.noaa.gov)
In fact, droughts may become so widespread and so severe that current drought indices may no longer be adequate to quantify them. (skepticalscience.com)
To monitor, detect and quantify drought, many drought indices have been developed. (phys.org)