Part 1: Overview
Drought is a stealthily incremental disaster that is much more costly to the national economy than most people suspect.
Even as the eastern states have seen an unusually wet summer, citizens in the midsection of the country read in May that the High Plains Aquifer could no longer support irrigation for vast stretches of farmland in Texas and Kansas (New York Times, 5/19). In June residents of the upper Midwest read with particular interest a story of how drought and other factors have created historically low water marks for the nation’s Great Lakes, putting a $34 billion shipping industry in peril (Seattle Times, 6/15). In August, citizens of the Southwest, many of whom depend on water from the Colorado River basin, read that the low water levels of Lake Mead would be minimally recharged by a record-low annual release of water from upstream reservoir Lake Powell, the latest outcome of a 14-year drought (Las Vegas Sun, 8/15).
Landsat image collection
According to a report by the National Drought Forum, more than 65 percent of the conterminous U.S. was affected by drought in 2012. The report notes that costs associated with the 2012 drought could be greater than losses from Superstorm Sandy, which makes the 2012 drought one of the top three costliest natural disasters since 1980. Widespread drought during 2012 in Texas alone resulted in $12 billion in damages.
What sections of the Nation are currently experiencing drought? How do those conditions compare to recent years, to the past century, or to more distant centuries? How can communities better prepare for and cope with drought? These are some of the questions USGS scientists consider as they work to understand the nature of drought and how to minimize its impacts.
USGS partners in the science of drought
The USGS works together with nearly 2,000 local, State, Tribal, and other Federal partners to pioneer new monitoring, assessment, and research capabilities, and develop innovative methods, tools, and mapping needed to address drought issues and management strategies across the Nation.
USGS science — conducted both in “real time” and over the long term — helps inform decision makers in communities across the country who have to deal complex issues and competing interests in times of drought. They need accurate, trusted information to:
Real-time data for real-time response
During a severe drought, communities and water managers must decide, for example, whether to restrict certain categories of water use; to hold water in reservoirs for the future or release it to satisfy immediate water needs; or to increase ground-
water pumping to augment surface-water supplies. These critical decisions require accurate and timely information that USGS provides on the current status and recent trends in streamflow, ground-water level, and water use.
USGS has worked with the State of Pennsylvania for more than a decade to develop a real-time system routinely used in State drought management applications. The tool is instrumental in continuously tracking precipitation, surface water, groundwater, and soil moisture, and highlighting the resource most affected at any given time.
A complex picture
The threshold of drought varies from place to place. USGS maps and graphs comparing current conditions to historical observations are available for nearly 4,000 long-term streamgages located in every State across the Nation (see Texas example in graph).
While streamflow may be the most readily apparent evidence of drought, it is not the whole picture. USGS real-time information on groundwater levels demonstrates clearly that precipitation deficiencies (and subsequent drought) affect different parts of the hydrologic system over time.
Effects of a drought on streamflows may happen fairly quickly – within days, or at most weeks or months. Groundwater levels in wells, however, may not reflect a shortage of rainfall for a year or more after a drought begins.
The USGS “Below Normal Groundwater Level” map for early August (see map) shows areas with below normal groundwater levels extending throughout the U.S., in contrast to drought maps of surface water showing impacts mostly in the west. This pattern is consistent with the recognition that groundwater levels are the last component of the hydrologic system to respond to the start and to the end of droughts. Read more about drought and other USGS groundwater activities.
Tracking drought from space
In addition to ground-based observations of hydrologic response in our surface and groundwater resources, USGS provides remote sensing data from earth observing satellites to evaluate drought conditions. The Vegetation Drought Response Index (VegDRI) integrates space-based observations of vegetation with other information about climate, land cover-land use, ecological setting, and soil characteristics to show drought’s effect on vegetation at a 1-kilometer resolution.
A time series of VegDRI maps for 2013 shows that in late August that the drought was far from over in the western states because of long-term rainfall deficits. Even though recent rains helped, conditions continue to degrade in the northern sections of the western region, including Idaho, western Montana, and northern Utah. In addition, because of the long-term rainfall deficits, moderate to severe drought was observed across the region, including Oregon, California, Nevada, Wyoming, Colorado, Arizona, and New Mexico.