The Application of Triggers in Drought Management: An Example from Colorado
Taryn Finnessey and Nolan Doesken
This chapter describes a state perspective on drought and explains how one state, Colorado, has learned to use climatic data and monitoring tools to create and use various drought indexes to track water supplies and then trigger actions—all for the purpose of guiding mitigation and response activities.
Colorado's interior continental location means that maritime moisture sources are distant, and atmospheric water supplies are not reliable. This results in a largely semiarid climate where the presence or absence of a few storms each year is the difference between a year with adequate water or a year of shortage. Colorado's mid-latitude location, high overall elevation, and tall mountain ranges mean that snow is a critical part of water supply. The mountain snowpack accumulates over a 6- to 8-month period. For some users, like the state's vast winter recreation industry, the timing of snow accumulation and melt is critical. But for many other users, such as agriculture and municipal water providers, it doesn't matter as much when the snow falls so long as there is enough water in the mountain snowpack by late spring. Then, in several weeks from late April into early July, the mountain snowpack quickly melts, providing the bulk of the entire year's water supplies. Spring rains at lower elevations, summer thunderstorms, and occasional widespread soaking rains in autumn have the potential to make up for occasional and sometimes extreme shortages in winter snowpack. (This is in contrast to California, where there is only one wet season.) But not all of Colorado is watered from melting snow. For many lower-elevation grassland and forest environments, if the spring rains do not materialize and summer thunderstorms are limited, extreme drought can develop quickly.
The result of these factors is that moderate or greater drought is present in some part of Colorado for some portion of the year in more than 9 out of 10 years (McKee 2000). This is the climatic background from which this case study begins.
Perhaps the most complex aspect of drought is that it develops relatively slowly over periods of weeks, months, and even years. Drought commonly extends over multiple seasons and years. Even the professionals whose job it is to track drought often do not know for sure that a drought has started until it is well developed, and they often do not know when it has ended until they look back on it. Other natural disasters (including floods, earthquakes, hurricanes, landslides, and blizzards) have clearly defined beginning and end points and require fairly specific responses. This is not the case with drought, which may mask itself as prolonged nice (i.e., sunny) weather. As a result, the detection of impacts is sometimes the first indication that a drought is occurring. This presents serious challenges as it results in a reactionary response rather than a phased and incremental one. Moreover, a reactionary response is solely focused on crisis management and does not focus on long-term impact reduction through the implementation of risk management actions. This may result in higher costs to individuals, society, and the environment. Evidence shows that dealing with disaster while in the midst of it can be more costly than proactive measures and can lead to less than ideal solutions (Multihazard Mitigation Council 2005). Consequently, there have been significant efforts to promote earlier detection and earlier response to drought.
The State of Colorado adopted its first formal "Drought Response Plan" in 1981 during the second extreme winter snow drought in a 5-year period (1976-1977 and 1980-1981). Both of these droughts occurred during the administration of Governor Richard (Dick) Lamm and during a period of very rapid population growth in Colorado and growth in the ski industry. From the very start, Colorado attempted to use a combination of thorough climate and water supply monitoring in combination with a quantitative approach to triggering actions and responses to drought. From these beginnings, Colorado has gone on to improve approaches and stimulate the development of better measures and indexes, and has developed a much more comprehensive drought mitigation and response plan (Colorado Water Conservation Board 2013) that not only incorporates a multistage response framework but also details monitoring methods, mitigation actions, and vulnerabilities. This multifaceted approach evolved through decades of experience, and was developed with the intent of reducing impacts and costs by enabling earlier response to drought through specific monitoring of indices and predetermined trigger points for action.