Monitoring Drought

 What is Climatology?

“Climate is what you expect. Weather is what you get.”
Weather is the condition of the atmosphere over a brief period of time. For example, we speak of today’s weather or the weather this week. Climate represents the composite of day-to-day weather over a longer period of time.

People in Minneapolis–St. Paul expect a white Christmas, and people in New Orleans expect very warm, humid summers. And a traveler going to Orlando, Florida, in March will not pack the same kind of clothing as a traveler going to Vail, Colorado, in March. These examples show how climate influences our daily lives. Additionally:

• Our houses are designed based on the climate where we live.
• Farmers make plans based on the length of the growing season from the last killing freeze in the spring to the first freeze in the fall.
• Utility companies base power supplies on what they expect to be the maximum need for heating in the winter and the maximum need for cooling in the summer.

A climatologist attempts to discover and explain the impacts of climate so that society can plan its activities, design its buildings and infrastructure, and anticipate the effects of adverse conditions. Although climate is not weather, it is defined by the same terms, such as temperature, precipitation, wind, and solar radiation.

Climate is usually defined by what is expected or “normal”, which climatologists traditionally interpret as the 30-year mean. By itself, “normal” can be misleading unless we also understand the concept of variability. For example, many people consider sunny, idyllic days normal in southern California. History and climatology tell us that this is not the full story. Although sunny weather is frequently associated with southern California, severe floods have had a significant impact there, including major floods in 1862 and 1868, shortly after California became a state. When you also factor in severe droughts, most recently those of 1987–94, a more correct statement would be that precipitation in southern California is highly variable, and that rain is most likely between October and April.

The misconception that weather is usually normal becomes a serious problem when you consider that weather, in one form or another, is the source of water for irrigation, drinking, power supply, industry, wildlife habitat, and other uses. To ensure that our water supply, livelihoods, and lives are secure, it is essential that planners anticipate variation in weather, and that they recognize that drought and flood are both inevitable parts of the normal range of weather.

How Does Climatology Help Us Prepare for Drought?
Climatology provides benchmarks, such as the drought of record. The drought of record is the drought remembered as having the greatest impact on a region. Most of us are not consciously aware of how much the climate fluctuates from one decade or century to the next. One way for reservoir managers, municipal water suppliers, and other planners to check reality is to compare expectations of water supply against a region’s drought of record. But caution is necessary here: although the weather conditions could recur, the impacts would likely be very different. For most of the country, the drought of record was 30 to 60 years ago, and population concentrations and water use patterns have shifted substantially since then. Planners need to consider and watch out for a variety of problems and misconceptions.

Specifically, climatology answers crucial questions such as:

• How often does drought occur in this region?
• How severe have the droughts been?
• How widespread have the droughts been?
• How long have the droughts lasted?

Examining water supplies and understanding the impact of past droughts help planners anticipate the effects of drought:

• What would happen if the drought of record occurred here now?
• Who are the major water users in the community, state, or region?
• Where does our water supply come from and how would the supplies be affected by a drought of record?
• What hydrological, agricultural, and socioeconomic impacts have been associated with the various droughts?
• How can we prepare for the next drought of record?