The National Weather Service defines drought as "a period of unusually persistent dry weather that persists long enough to cause serious problems such as crop damage and/or water supply shortages." It is important to note that there are several different types of drought and the term is used differently by, say, a weatherman and an urban planner. The different types can be defined as follows:
Meteorological drought occurs when precipitation is less than average. Due to variations in climate over large areas, a drought in one location does not necessarily imply a drought in another location. Thus, one watershed can experience a drought while an adjacent watershed experiences average precipitation levels.
Hydrological drought occurs when surface and groundwater supplies fall below the statistical average.
Agricultural drought occurs when the soil moisture content is less than is needed to support a particular crop. This condition can exist independent of precipitation levels.
Socioeconomic drought occurs when physical water shortages begin to affect people directly.
A definition of drought could also very well include the impact of demand upon water supplies. For example, a hydrological drought can occur even when precipitation levels are average if domestic water use increases due to population growth. The same demand is placed upon water when it becomes polluted, when agricultural use increases, when residents fail to conserve water, et cetera.
Drought and the Beaver Creek Watershed
Its location in the arid southwestern U.S. makes the Beaver Creek Watershed especially sensitive to drought conditions. Because the perennial surface waters are largely fed by springs, large drops in groundwater levels would cause those springs and, hence, the creek to run dry. If the regional aquifer should drop below the level of the Coconino Sandstone, the unit that supplies the majority of water to the creek, the creek would cease to be perennial. This is especially important to residents of the Verde and Salt River Valleys, who rely largely upon the Salt and Verde Rivers for their municipal water supplies.
Perennial streams of the Mogollon Rim such as Beaver Creek are the primary contributors of surface water flow to the Verde River, which in turn feeds the Salt River. In turn, the groundwater that feeds the springs in Beaver Creek is recharged, or replenished, at higher latitudes within the Colorado Plateau. This means that a local hydrological drought on the Plateau, whether caused by decreased precipitation or increased use, can affect the Mogollon Rim streams, which in turn feed the Verde and Salt River Valley streams. Thus, the interconnectedness of watersheds within the area is of particular importance to water managers.
American Rivers, a Washington, D.C.-based watchdog group, recently listed the Upper Verde River as the 10th most endangered American river in its annual report entitled America's Most Endangered Rivers. Their listing was based on the degree of groundwater pumping that takes place in the watershed, ultimately affecting the surface flow; and the projected growth for the area will place a higher demand on that water well into the future.
Drought and Fire
Just as importantly, drought leaves vegetation more susceptible to fire. After one season of less than average precipitation, the volatility of ponderosa pine and pinyon-juniper vegetation increases significantly. Fire suppression policies throughout the 20th century have resulted in densely populated vegetation that must compete for water supplies. This dense vegetation provides a wealth of fuel during fire season, resulting in much more intense fire than would be experienced with a normal population. In addition, ponderosa pine are vulnerable to bark beetle infestations when they are weakened by a lack of water. The beetles further weaken the trees by inhibiting their ability to transport water and nutrients through their systems, ultimately resulting in the trees' death.
Though the riparian vegetation immediately along the streambanks is more resistant to fire, burning away the pinyon-juniper vegetation surrounding the creek leaves the watershed more susceptible to erosion. Increased erosion results in increased sedimentation, which can alter the equilibrium of the aquatic ecosystem. Thus, a series of cause-effect relationships can result in something similar to a chain reaction that may be unstoppable if we do not manage fragile watersheds like Beaver Creek wisely. Therefore, Beaver Creek serves as an invaluable educational tool for researchers, the general public, and land managers alike.