The Ongoing Drought in the Southwest

Introduction

As populations continue to grow in the United States and throughout the world, demand for water is constantly increasing. During the past 50 years, groundwater depletion has spread from isolated pockets to large areas in many countries. Added to the population increases and the increased demands for groundwater are the effects of drought. In recent years, many areas of the United States have suffered severe droughts. During such periods, more water must be drawn from the ground to irrigate yards and farms, however, because rainfall is reduced, groundwater is not replenished.

Water is certainly one of the defining environmental issues in the West today. In a region marked by increasing and shifting population, increasing urbanization, changing trends and patterns of water use, and growing environmental awareness, water is and will continue to be a source of conflict and controversy. Unfortunately, you may not know you’re in a drought until you are many months into it, and as it continues, it slowly takes a greater and greater toll. Increased environmental awareness and improved conservation practices like the ones outlined in this newsletter can make a difference. With proper preparedness, the effects of drought can be minimized.

What Is Drought

Drought is a normal, recurrent feature of climate. It occurs almost everywhere, although its features vary from region to region. Defining drought is therefore difficult; it depends on differences in regions, and needs. Based on the many definitions that have appeared in the literature, for example, we might define drought in Africa as occurring when annual rainfall is less than 7 inches, but in Indonesia, drought might be considered to occur after a period of only 6 days without rain! In the most general sense, drought originates from a deficiency of precipitation over an extended period of time, resulting in a water shortage for some activity, group, or environmental sector.

Monitoring Drought

Given the recent improvements in access to information over the Internet, the recent drought has generated a considerable interest in drought and in sources of information about drought monitoring and forecasts. A wide range of agencies and organizations provide such information for the United States. Perhaps the most comprehensive current drought status assessment is the U. S. Drought Monitor (Figure 1). The Drought Monitor is a weekly synthesis of many kinds of climate information (such as drought indices, precipitation, snow, and temperature data), along with drought impact information and expert assessment by federal, state, and academic scientists.

Figure 1 U.S. Drought Monitor

Water Resources and Climate Change

Although we don’t know how climate change will affect regional water resources, it is clear that water resources are already stressed, independent of climate change and any additional stress from climate change or increased variability will only intensify the competition for water resources. Current stresses on water resources include:

• growing populations,

• increased competition for available water, and

• groundwater overdraft.

In all likelihood, the direct impacts of climate change on water resources will be hidden beneath natural climate variability. With a warmer climate, droughts and floods could become more frequent, severe, and longer-lasting. The potential increase in these hazards is a great concern given the stresses being placed on water resources and the high costs resulting from these hazards.

Dealing with Drought

The Southwest is known for its diverse landscapes and semiarid climate. The frequent occurrence of extreme hot and dry conditions, such as drought, is a normal part of the region’s climate. Following several years of below average precipitation, Arizona faced extreme drought during the 2002 water year (i.e., October 2001 to September 2002) the driest water year on record for many parts of the state. Impacts included 629,876 acres lost to wild land fire in 2002, water supply shortages, vegetation and wildlife mortality, and economic losses in the ranching, agriculture, and tourism sectors. As a result of these impacts, Arizona Governor Janet Napolitano created the Governor’s Drought Task Force by executive order 2003-12 in March 2003, and approved in October 2004 to identify and plan responses to potential problems resulting from the current drought. Arizona is the 36th state to develop a state drought plan in the United States. Among the issues being evaluated are:

• potentially low supplies of potable water for water providers,

• drought-related water level declines that can cause a loss of supply for individual domestic wells,

• insufficient water supply for crops and livestock, and

• impacts to wildlife and wildlife habitat due to reduced availability of water.

All of these issues are of interest to the residents of the Globe-Miami area, including the Pinal Creek Group, as we work to manage our water resources wisely.

Arizona has been subject to several major statewide droughts occurring from the late 1890s through the early 1900s, the late 1940s through the mid-1960s, and the current cycle that began in the late 1990s. Droughts such as these result from below-normal rainfall and snowfall, and consequently, less runoff to surface water streams and less recharge to groundwater aquifers. The affect of these droughts on surface water in Arizona is illustrated by the change in 5-year annual running average stream flow of the Salt River, as shown in Figure 2.

Figure 2. The red line shows annual average streamflow at the U.S. Geological Survey Salt River gauging station near Roosevelt Lake. Note that streamflow was frequently less than the long term average during the drought between 1942 and approximately 1964. By comparison, streamflow was higher than the long term average during the wet period of the 1980s and early 1990s. The lowest streamflow of record occurred in 2002.

When drought occurs, water levels in groundwater aquifers can drop significantly. The graph in Figure 3 illustrates the water level in the Gila Conglomerate near Wheatfields. The increase in water levels during the rainy period of the early 1990s is clearly shown, as is the continued decline of low water levels through the current drought period.

These data show that large changes (at least 75 feet) in the depth to water can occur naturally due to wet and dry cycles of weather. It could take several years to replenish the groundwater supply depending on the degree to which water is depleted from the rate at which it is recharged to the aquifer.

During a sustained drought, a substantial drop in ground-water levels due to reduced aquifer recharge can place small capacity domestic wells at risk of lowered production or going dry. During times of lower than normal water levels, overlapping pressure from other, nearby pumping wells can cause further water level decline. Unfortunately, these effects of drought on groundwater supplies are to be expected in the arid Southwest. Water conservation and good well maintenance practices are essential to minimize the affects of drought on water supplies dependent on groundwater.

Figure 3. This graph shows the depth to groundwater in Gila Conglomerate in two closely spaced wells near the confluence of Pinal Creek and Miami Wash. A water level increase of approximately 20 feet in response to rainfall recharge occurred over six months between November 2004 and April 2005.