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Donald A. Wilhite

Abstract

Drought relief has become an expected response of the federal government to periods of widespreaddrought in the United States. A wide range of emergency, short-term and long-term drought programs wereformulated to deal with the extreme drought of the 1930's. By 1977 there were 40 separate programsadministered by 16 different federal agencies. This paper traces the development of federal drought reliefbureaucracy, including drought designation criteria and procedures.

Two obvious deficiencies of past drought relief efforts in the United States are noted. First, drought relieforganizations and programs have been hastily assembled during periods of crisis. This has resulted in reducedprogram effectiveness as implementation has often been delayed pending program formulation and congressional approval. Second, previous efforts have had no adequate and systematic provision of timely information on drought conditions and impacts to persons or agencies involved in administering drought programs. The design, implementation and evaluation of a near real-time drought surveillance and early warningsystem is mentioned as one way atmospheric scientists can contribute to improved drought response in theUnited States.

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Hi-Ryong Byun
and
Donald A. Wilhite

Abstract

Common weaknesses of current drought indexes were analyzed. First, most of the current indexes are not precise enough in detecting the onset, end, and accumulated stress of drought. Second, they do not effectively take into account the aggravating effects of runoff and evapotranspiration, which build up with time. Third, they have a limited usefulness in monitoring ongoing drought because they are based on a monthly time step. Fourth, most of them fail to differentiate the effects of drought on surface and subsurface water supply.

A new series of indexes are proposed to solve these weaknesses and to improve drought monitoring. In the new indexes, daily, rather than monthly, time steps are used. A new concept, effective precipitation (EP), the summed value of daily precipitation with a time-dependent reduction function, is proposed as a basic tool.

Three additional indexes complement EP. The first index is each day’s mean of EP (MEP). This index shows climatological characteristics of precipitation as a water resource for a station or area. The second index is the deviation of EP (DEP) from the MEP. The third index is the standardized value of DEP (SEP). By using these three indexes, consecutive days of negative SEP, which can show the onset, the ending date, and the duration of a water deficit period is categorized.

With the duration categorized, four additional indexes that can show drought severity are calculated: 1) accumulation of consecutive negative SEP, which shows the duration and severity of precipitation deficit together;2) accumulated precipitation deficit, which shows precipitation departure from the normal during a defined period; 3) precipitation for the return to normal; and 4) effective drought index, a standardized index that can be used to assess drought severity worldwide. The merits and weaknesses of each index are compared. New quantified definitions on drought and its onset, end, and duration are proposed.

These indexes were tested in the High Plains region of the United States from 1960 to 1996. The results were compared to historical reports of drought. From this analysis, it was concluded that the new indexes not only advanced objectivity, but also offered a number of advantages in practical use. These are 1) a more precise determination of drought duration, 2) the usefulness in monitoring an ongoing drought, and 3) the variety of ways a drought’s characteristics can be described.

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Donald A. Wilhite
,
Norman J. Rosenberg
, and
Michael H. Glantz

Abstract

Severe and widespread drought occurred over a large portion of the United States between 1974 and 1977. Impacts on agriculture and other industries, as well as local water supplies, were substantial. The federal government responded with forty assistance programs administered by sixteen federal agencies. Assistance was provided primarily in the form of loans and grants to people, businesses and governments experiencing hardship caused by drought. The total cost of the program is estimated at $7–8 billion.

Federal response to the mid-1970s drought was largely untimely, ineffective and poorly coordinated. Four recommendations are offered that, if implemented, would improve future drought assessment and response efforts: 1) reliable and timely informational products and dissemination plans; 2) improved impact assessment techniques, especially in the agricultural sector, for use by government to identify periods of enhanced risk and to trigger assistance measures; 3) administratively centralized drought declaration procedures that are well publicized and consistently applied; and 4) standby assistance measures that encourage appropriate levels of risk management by producers and that are equitable, consistent and predictable. The development of a national drought plan that incorporates these four items is recommended. Atmospheric scientists have an important role to play in the collection and interpretation of near-real time weather data for use by government decision makers.

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Steven J. Meyer
,
Kenneth G. Hubbard
, and
Donald A. Wilhite

Abstract

In a recent survey conducted by the University of Nebrask's Center for Agricultural Meteorology and Climatology of Agricultural Network (AGNET) users, the results of potential evapotranspiration (ET p ) projections (calculated using the Blaney-Criddle approach, which employs “normal” climatic data to project ET p , estimates up to three days into the future) were labeled “unrealistic”. To improve these projection National Weather Service (NWS) forecast variables were used as input into the Blancy-Criddle and Penman equations. ET p , projections calculated according to the Penman equation, with data measured by automated weather stations as input, were assumed to represent the “best” attainable. ET p projections calculated using NWS forecasted values were compared with the “best” projections for the summer of 1985. Increased accuracy in ET p , projections due to increased accuracy in the individual forecasted input variables was evaluated.

Overall, daily ET p , projections made with the Blancy-Criddle equation were substantially improved using the NWS forecasted temperature in place of normal temperature; over a growing season, however, accurate estimates resulted from using normal temperatures. The use of NWS-forecasted variables as input into the Penman equation offers the greatest potential for improving ET p , projections. “Over” forecasting of all variables (relative to the estimation of ET p ,) limited the ability of the Penman equation in this study. For greatest improvement in ET p , projections using the Penman equation, efforts should be concentrated on improving forecasts of relative humidity and solar radiation.

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Donald A. Wilhite
,
Kimberly C. Morrow
, and
Martha Shulski
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Tsegaye Tadesse
,
Donald A. Wilhite
,
Michael J. Hayes
,
Sherri K. Harms
, and
Steve Goddard

Abstract

Drought is a complex natural hazard that is best characterized by multiple climatological and hydrological parameters. Improving our understanding of the relationships between these parameters is necessary to reduce the impacts of drought. Data mining is a recently developed technique that can be used to interact with large databases and assist in the discovery of associations between drought and oceanic data by extracting information from massive and multiple data archives.

In this study, a new data-mining algorithm [i.e., Minimal Occurrences With Constraints and Time Lags (MOWCATL)] has been used to identify the relationships between oceanic parameters and drought indices. Rather than using traditional global statistical associations, the algorithm identifies drought episodes separate from normal and wet conditions and then uses drought episodes to find time-lagged relationships with oceanic parameters. As with all association-based data-mining algorithms, MOWCATL is used to find existing relationships in the data, and is not by itself a prediction tool.

Using the MOWCATL algorithm, the analyses of the rules generated for selected stations and state-averaged data for Nebraska from 1950 to 1999 indicate that most occurrences of drought are preceded by positive values of the Southern Oscillation index (SOI), negative values of the multivariate ENSO index (MEI), negative values of the Pacific–North American (PNA) index, negative values of the Pacific decadal oscillation (PDO), and negative values of the North Atlantic Oscillation (NAO). The frequency and confidence of the time-lagged relationships between oceanic indices and droughts at the selected stations in Nebraska indicate that oceanic parameters can be used as indicators of drought in Nebraska.

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M. V. K. Sivakumar
,
Donald A. Wilhite
,
Roger S. Pulwarty
, and
Robert Stefanski
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Qi Hu
,
Lisa M. Pytlik Zillig
,
Gary D. Lynne
,
Alan J. Tomkins
,
William J. Waltman
,
Michael J. Hayes
,
Kenneth G. Hubbard
,
Ikrom Artikov
,
Stacey J. Hoffman
, and
Donald A. Wilhite

Abstract

Although the accuracy of weather and climate forecasts is continuously improving and new information retrieved from climate data is adding to the understanding of climate variation, use of the forecasts and climate information by farmers in farming decisions has changed little. This lack of change may result from knowledge barriers and psychological, social, and economic factors that undermine farmer motivation to use forecasts and climate information. According to the theory of planned behavior (TPB), the motivation to use forecasts may arise from personal attitudes, social norms, and perceived control or ability to use forecasts in specific decisions. These attributes are examined using data from a survey designed around the TPB and conducted among farming communities in the region of eastern Nebraska and the western U.S. Corn Belt. There were three major findings: 1) the utility and value of the forecasts for farming decisions as perceived by farmers are, on average, around 3.0 on a 0–7 scale, indicating much room to improve attitudes toward the forecast value. 2) The use of forecasts by farmers to influence decisions is likely affected by several social groups that can provide “expert viewpoints” on forecast use. 3) A major obstacle, next to forecast accuracy, is the perceived identity and reliability of the forecast makers. Given the rapidly increasing number of forecasts in this growing service business, the ambiguous identity of forecast providers may have left farmers confused and may have prevented them from developing both trust in forecasts and skills to use them. These findings shed light on productive avenues for increasing the influence of forecasts, which may lead to greater farming productivity. In addition, this study establishes a set of reference points that can be used for comparisons with future studies to quantify changes in forecast use and influence.

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