Drought Monitoring and Early Warning: Twenty-First Century Advancements and Challenges

Introduction: The Importance of Drought Early Warning

Water crises were identified as the top global risk facing society over the next 10 years according to a recent survey of 750 of the world's leading economists (World Economic Forum 2016). As a normal natural hazard in most climates, drought will compound these crises and play a fundamental direct or indirect role in water stress issues occurring around the world, particularly given that droughts are expected to increase in frequency and intensity as a consequence of climate change (Glotter and Elliott 2016). Water stress issues are prevalent across the United States. For example, increasing growth and development continue to strain water supplies not only for the major metropolitan areas of the arid West but also for metropolitan areas in the relatively humid eastern

United States. Issues surrounding shared water resources across international boundaries, such as the Colorado and Rio Grande river basins between the United States and Mexico, and the Great Lakes and Columbia River basins between the United States and Canada, will also continue to grow. Therefore, because of serious drought impacts on water resource-related issues, planning for and responding effectively to future droughts is critically important within the United States and around the world.

Drought early warning is a key component within a drought risk management approach, which can help planners and decision makers break the hydro-illogical cycle (see Chapter 4). While drought monitoring involves the continuous assessment of the natural indicators of drought severity and spatial extent, drought early warning refers to the use of that information to produce an appropriate and timely response (Hayes et al. 2012). A drought early warning system, which combines both assessment and decision-maker response, provides decision makers accurate early warning information to implement effective drought policies and response and recovery programs. The components of a drought early warning system vary and can be adapted for any region. Generally, these components include an operational drought monitoring network, access to timely data, "value-added" analyses, synthesis, and dissemination of data that can then be used and integrated into decision support tools, communication strategies, and educational efforts (Hayes et al. 2012). Decision makers also benefit from short- and long-term drought forecasting tools that allow them to anticipate and respond to a drought event with better understanding and confidence, and these forecasting tools should be incorporated into a drought early warning system.

One constraint to effective drought early warning has always been the lack of a universally accepted definition for drought. Scientists and decision makers must accept that the search for a single definition of drought is a hopeless exercise. Drought definitions must be specific to the region, application, or impact. Drought must be characterized by many different climate and water supply indicators, and an effective early warning system must build on these indicators (see also Chapter 10). Impacts are complex and vary regionally, and at a variety of timescales. Drought monitoring indicators, ideally, should be tied directly to triggers that assist decision makers with timely and effective responses both before and during drought events.

Recent widespread and severe droughts resulting in serious economic, social, and environmental impacts in many countries highlight the need for continual improvement in drought early warning systems. In the United States, these droughts have fostered development of improved drought monitoring data, decision support tools, and collaborations between scientists. This chapter discusses some of these new developments, as well as the current status of drought forecasting in the United States. The chapter also provides an opportunity to recognize one of the true heroes of drought early warning, author Kelly Redmond. Dr. Redmond passed away on

November 3, 2016, following a very distinguished climatology career. On the topic of drought early warning, Dr. Redmond provided tremendous leadership, guidance, and wisdom. He was known for his ability to verbalize complex issues in simple and witty terms, and one of his favorite quotes directly applies to drought early warning: "An ounce of observation is worth a pound of forecasts" (Redmond 2014). As the quote suggests, Dr. Redmond was an emphatic proponent of the value of drought monitoring systems within the context of early warning.

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