In LA, they experienced below average rainfall for 4 out of 6 years during 1998-2004, and 2 out of 6 years they were barely above average. During 2005, they experienced a very large amount of rainfall, but most of the extra rainfall was lost due to runoff and it was not usable for humans. One of the problems Southern California faces is that 30-40% of water supply is from groundwater, and the over extraction of groundwater in LA has lead to saltwater leakage from coastal aquifers.
Thus, a barrier needs to be created between the saltwater and freshwater so people can drink the groundwater and that process is expensive. Additionally, the Colorado River is a major source of water for Southern California. So if there’s a drought over the West and Midwest, Southern California has less water from its own state and less water coming in from the Colorado River aqueduct.
Even though these preventative measures may be helpful to the ecosystem, the drought is inevitable.
Through tree ring data, and history, we can find that the drought is a natural process. With tree ring data, scientists use limber pines that are around 1300 years old and deadwood trees that are around 2000 years old to see what the water availability was in the past. They used winter monthly precipitation data and made a Palmer drought severity index, which tells you how severe the drought was at a certain time. They found through data, that between 975-1075, 1120-1160, and 1282-1342, there were moderate to severe droughts lasting 40 or more years, which is unheard of during the last 200 years of recorded history.
The prolonged droughts found in the trees used in the study, were similar to other tree ring records in Northern California and western North America.
With that being said, 2014 was found to be the most severe while looking at the Palmer Drought Severity Index, which is located on the picture. The vertical axis shows the Index, zero is neither a dry or wet season, above zero means it was a wet season and below zero means it was a dry season. Ignore the precipitation anomaly on the bottom because that is just scaling how rare or not rare the rainfall is that year with respect to it being a dry or wet season. In 2011 california was not in a drought, but as the years progress it got worse and worse and they happened to be in a drought in 2014.So while this drought was really bad in 2014, there have been other years that have been nearly as bad.
Now I will move on about the history of people living in California and how the history shows that droughts are not uncommon. In LA, a relatively short period of drought occurred in 1862-1864 which caused a loss of 70% of cattle for the whole country. At the time, cattle ranching was a very successful economic activity in Southern California. The drought that occurred was responsible for not only shifting the economy in a different direction, but it stripped people living in California of their land and standing in their society. Because of the drought, citizens were forced to make pipes and irrigation systems instead of having Zanjas, which are water ditches. This benefited everyone temporarily, but as populations grew, they had to make aqueducts to bring water into the city. (SLIDE) Today in california, 75% of the population is below Sacramento, when 75% of the precipitation in California receives is above Sacramento. Luckily, these aqueducts are able to lead water from upper California to provide LA water, but as of late, LA may need some more technology to provide water to all of its citizens. In the 1800s and 1900s people made advances to get water, and now it looks like we may need to make more advances to keep LA from going dry and thirsty.
We can conclude the drought is not uncommon by looking at the data from the middle ages and this graph. This graph shows that there are way more dry seasons than wet season and a similar thing occurred in the middle ages. So it’s most likely we have to adapt to the droughts right now because there may be more severe droughts in the future.