measures current conditions such as temperature, moisture and wind while climate
measures those for a long period for a certain area. Nowadays, climate is undergoing
a major change. California has a Mediterranean climate. “Mediterranean climates
have most precipitation in winter when temperatures are low” (Lecture 2 slide
65). In 2014, the mayor of California declared a state emergency of drought. Drought
comes when winter rains are less than average and when summers are hotter than
average. The drought from 2010-2015 was not the worst in California’s history
as the state had 150 years of drought during the Medieval Warm Period. The
Medieval Warm Period likely occurred around 950-1100 AD in the Northern
Hemisphere (Wikipedia, 2017). Evidence by paleo-climatic and model data
suggests that Medieval Warm Period (MWP) can be used to relate to the
possibility of similar distressed conditions in the future for California. (Woodhouse,
2009) Extreme weather is increasing in the hotter world of global warming. As
2016 was the warmest year on record (lecture 3, slide 39), it had a direct
impact on the increasing of drought and other extreme events. We can measure today’s drought by the Palmer
Drought Severity Index or PDSI. This index “determines long-time drought especially
over low and middle latitude” (Dai, Aiguo, 2017). It also cares for the past
conditions that are related to climate changes and evapotranspiration. Is
California’s climate in 2018 going to be dry? Are we going for another state of
emergency this year? How would a really wet or dry 2018 affect the trends? Can
California’s residents begin to not worry too much about their water usage



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PDSI has been
previously described as a measure to estimate relative dryness.

This method is
calculated to “capture the basic effect of global warming on drought through
changes in potential evapotranspiration”. (National Center for Atmospheric
Research Staff, 2017). Severe drought is
classified as -3 and extreme drought in as -4 on the PDSI scale. At the other
end, very moist is >3 and extremely moist is >4. Values below -4 are
extremely rare in the US. Regression with positive slope would indicate
increasing wetness of the California weather and a new climate. The opposite
holds for negative slope, a trend of drier years and continued drought.


Results. The data in Figure 1 on page the last page shows that
within the last 122 years the PDSI values are generally slowly decreasing. It
also shows how between 2010-2015 there was severe/extreme drought and in 2016
there was enough rain for the State of California to be very moist. The trend
in the linear line is negative and the p-values are greater than 0.05. The line
also has a slope that is not equal to zero which means that the regression line
is not statistically significant. The LOWESS lines are also decreasing at f=1
and f=0.5. It is hard to indicate if California is out of the drought at this



The Medieval warm period is a period that a lot of people
would consider when discussing global warming. “The causes of past and
future drought will not be identical but warm droughts, inferred from paleo-climatic
records, demonstrate the plausibility of extensive, severe droughts, provide a
long-term perspective on the ongoing drought conditions in the Southwest, and
suggest the need for regional sustainability planning for the future.”

Evidence of this extensive drought
in medieval years is also seen in stumps found in the Sierra Nevada lakes.

Until these stumps were located, the “Dust Bowl Period” which happened from
1928 until 1934 was considered the worst drought documented. The stumps were
discovered at the base of four lakes in the Sierra Nevada: Osgood Swamp, Mono
Lake, Tenaya Lake, and the West Walker River. These stumps show that these
bodies of water fell to extremely low levels a few times because of the lingering
drought (Stine, 1994).

Moreover, Jay Lund describes
California’s drought as persistent. He claims that the dry December a lot of
times means a drier year. He emphasizes that according to the historical statistics
of monthly precipitation in Northern California, maybe 2018 will be drier than
the median and drier than average. (Lund: 2017). He also claims that there is a
really small chance of flooding in the State but officials should not be
skeptical of it happening.