Abstract[Drought indicators are proliferating, but with little consideration of which are most meaningful for describing drought impacts. A number of recent reviews compare different drought indicators, but none assess which indicators are actually used in the many operational drought monitoring and early warning efforts, why they were selected, or whether they have been 'ground-truthed', i.e., compared with information representing local drought conditions and/or impacts. Also lacking is a comprehensive assessment of the state of monitoring of drought impacts. To help fill this gap, we combine a review of drought indicators and impacts with a survey of 33 providers of operational drought monitoring and early warning systems from global to regional scales. Despite considerable variety in the indicators used operationally, certain patterns emerge. Both the literature review and the survey reveal that impact monitoring does exist but has rarely been systematized. Efforts to test drought indicators have mostly focused on agricultural drought. Our review points to a current trend towards the design and use of composite indicators, but with limited evaluation of the links between indicators and drought impacts. Overall, we find that much progress has been made both in research and practice on drought indicators, but monitoring and early warning systems are not yet strongly linked with the assessment of wider impacts on the environment and society. To understand drought impacts fully requires a better framing of drought as a coupled dynamic between the environment and society.]

Severe drought is a recurring problem for the United States, as illustrated by widespread economic, social, and environmental impacts. Recent drought episodes and the widespread drought conditions in 1996, 1998, and 1999 emphasized this vulnerability and the need for a more proactive, risk management approach to drought management that would place greater emphasis on preparedness planning and mitigation actions. Drought planning has become a principal tool of states and other levels of government to improve their response to droughts. For example, since 1982, the number of states with drought plans has increased from 3 to 29. Many local governments have also adopted drought or water shortage plans. Unfortunately, most state drought plans were established during the 1980s and early 1990s and emphasize emergency response or crisis management rather than risk management. This paper presents a substantive revision of a 10-step drought planning process that has been applied widely in the United States and elsewhere. The revised planning process places more weight on risk assessment and the development and implementation of mitigation actions and programs. The goal of this paper is to encourage states to adopt this planning process in the revision of existing drought plans or, for states without plans, in the development of new plans.

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We used monthly precipitation and temperature data to give early warning of years with higher West Nile Virus (WNV) risk in Nebraska. We used generalized additive models with a negative binomial distribution and smoothing curves to identify combinations of extremes and timing that had the most influence, experimenting with all combinations of temperature and drought data, lagged by 12, 18, 24, 30, and 36 months. We fit models on data from 2002 through 2011, used Akaike's Information Criterion (AIC) to select the best-fitting model, and used 2012 as out-of-sample data for prediction, and repeated this process for each successive year, ending with fitting models on 2002-2017 data and using 2018 for out-of-sample prediction. We found that warm temperatures and a dry year preceded by a wet year were the strongest predictors of cases of WNV. Our models did significantly better than random chance and better than an annual persistence naïve model at predicting which counties would have cases. Exploring different scenarios, the model predicted that without drought, there would have been 26% fewer cases of WNV in Nebraska through 2018; without warm temperatures, 29% fewer; and with neither drought nor warmth, 45% fewer. This method for assessing the influence of different combinations of extremes at different time intervals is likely applicable to diseases other than West Nile, and to other annual outcome variables such as crop yield. Plain Language Summary We wanted to see whether we could predict years with higher risk of West Nile Virus in Nebraska using publicly available data on temperature, precipitation, human cases, and population. We used a type of model that lets the data speak for itself, identifying which intervals of time leading up to an infection season are most important. We found that a dry year following a wet year, often in combination with warm temperatures, increased the likelihood of infection. Drought accounted for about 26% of the number of cases from 2002 to 2018.

Capsule A pilot study found that #drought tweets reflect changes in attention to drought within states, suggesting that social media can contribute to a drought early warning system.