Weather and Climate The 1987-1992 Drought

Mount Shasta is located in far northern California at 41.3º N, 122.3º W. Mount Shasta has a Mediterranean climate, characterized by hot, dry summers and cold, wet winters. Most of the yearly precipitation falls during the winter season. Because of its high elevation and latitude, much of the winter precipitation falls as snow. This snowpack acts as a reservoir for the surrounding area, providing water to the Shasta River watershed to the north as well as to the Sacramento River watershed to the south. Northern California receives five to seven major storms during the wet season. If fewer than five storms hit the region, it is likely to lead to drought conditions (Bowling and Jercich, 1996).

North America as a whole has experienced numerous droughts. When pioneers first began settling the Great Plains, they were told that "rain follows the plow." However, it was an unusually rainy period. In the late 1880s drought struck and over half of the settlers lost their land. Many people are familiar with the Dust Bowl of the 1930s and the lesser drought of the 1950s. What many people don't recognize, however, is that over the past 400 years droughts equivalent to the 1950s drought have occurred several times per century (Priest et al., 1993; NOAA Paleoclimatological Program, 2000).

The extent and severity of the driest year of the Dust Bowl in the United States, 1934
Source: National Oceanic and Atmospheric Administration, 2000

The Palmer Drought Severity Index (PDSI) was mainly developed for use in agriculture. Maps showing PDSI indicate the severity, extent, and duration of a drought. Measurements used in calculating the PDSI are precipitation, temperature, and soil moisture (NOAA, 2000).

Short-term droughts commonly occur in California, but only two droughts have lasted for more than four years in northern California since record-keeping began in 1850. The first of the long-term droughts occurred from 1929 to 1934. The second major drought lasted from 1987 to 1992 and is considered the most severe drought in California's history (Priest, et al., 1993). Short-term droughts can also have severe impacts on the economy and environment. For example, the 1862-64 drought heavily impacted the developing cattle industry network in the American West (Young and Young, 1968) and the 1976-77 drought resulted in water-use regulations in California.

The 1976-77 short-term drought
Source: National Oceanic and Atmospheric Administration, 2000

The impact of the 1976-77 drought on Mount Shasta
Photograph by Ken Goehring, Fall 1977

The early 1980s were mostly above average in precipitation in northern California and throughout the West, with the wettest year of the decade occurring in 1983. The year of 1985 was somewhat dry, with a PDSI of -2 in northern California while 1986 was an average year with a PDSI of 0 in the Mount Shasta region.

The early 1980s were wet throughout the West
Source: National Oceanic and Atmospheric Administration, 2000

Animated view of 1987-1992 Drought
(Individual Maps)
Source: National Oceanic and Atmospheric Administration, 2000

Snow depth at Horse Camp in April for the years 1983-1992 is shown below. Average snow depth for this station during the drought period from 1987-1992 was 97 inches (246 cm) while average April snow depth from 1950-1999 was 127 inches (323 cm). The high snowfall during 1983 helped alleviate the severity of the 1987-1992 drought. The 1989 season didn't break the drought but it, too, reduced the overall severity of the drought.

In an earlier study (Freeman, 2000), it was found that the impact of the 1987-1992 drought could be detected in Shasta Valley using Multispectral Scanner (MSS) satellite data. Three MSS datasets were chosen to examine the effects of the 1987-1992 drought. All scenes selected had a cloud cover of less than 10% and were acquired in June for a better multi-temporal perspective. The earliest scene was gathered on June 29, 1974 prior to the short-term 1976-77 drought, yet forty years after the end of the last major drought in California (1934). This scene provides a view of the long-term average non-drought conditions in the region. The next scene was acquired on June 13, 1985. This scene was selected to be as far in time from the short-term 1976-77 drought, yet before the severe 1987-1992 drought. The last scene used in this study was gathered on June 8, 1992 to depict the most severe conditions of the 1987-1992 drought.

The results of the Shasta Valley study indicated that water covered 8.4% of the 1974 scene, 5.6% of the 1985 scene, and only 2.3% of the 1992 scene. Notice that even though the early 1980s were wetter than average, the water coverage in the Shasta Valley had not recovered from the short-term 1976-77 drought by 1985.

A Normalized Difference Vegetation Index (NDVI) shows the greenness of the vegetation (yellows to greens) as well as bodies of water and snow (browns to tans). If you compare the 1974 scene with the 1992 scene, you will notice that the 1974 scene has more snow on Mount Shasta and the lakes (most notably Lake Shastina and Siskiyou Lake) have more water in them. However, the vegetation appears greener in the 1992 scene. This may be due to irrigation.

Normalized Difference Vegetation Index for 1974 (left) and 1992 (right)

The 1987-1992 drought finally ended with the spectacular winter of 1992-93. By February 1993 there was already 125 inches (317.5 cm) of snow at Horse Camp compared with only 13 inches (33 cm) in 1991 and 41 inches (104 cm) in 1992. As a comparison, in February of 1974 there was 163 inches (414 cm).

Drought-breaking 1993
Source: National Oceanic and Atmospheric Administration, 2000

It might seem that a drought is insignificant compared to tornadoes and hurricanes. However, the meltwater from Mount Shasta seeps deep into the mountain and feeds the aquifers. Both the Klamath River system and the Sacramento system rely on its contribution. The salmon and other native wildlife and vegetation are dependent on the water, as is outdoor recreation, including fishing and winter sports. Also, the widespread wildfires of 1987 and 1988 (local fires as well as the Yellowstone Fire) are a direct result of the drought.

Water from Mount Shasta is also necessary for one of Siskiyou County's most important industries, agriculture. It is also important as a source of drinking water for locals and it is bottled for consumption in other parts of the world. Although droughts may not be as spectacular as other weather events, the 1987-1989 portion of the drought was the most expensive natural disaster in the United States to date, costing a total of $39 billion dollars for those years alone (NOAA, 2000).