Weathermeasures current conditions such as temperature, moisture and wind while climatemeasures those for a long period for a certain area. Nowadays, climate is undergoinga major change. California has a Mediterranean climate. “Mediterranean climateshave most precipitation in winter when temperatures are low” (Lecture 2 slide65).
In 2014, the mayor of California declared a state emergency of drought. Droughtcomes when winter rains are less than average and when summers are hotter thanaverage. The drought from 2010-2015 was not the worst in California’s historyas the state had 150 years of drought during the Medieval Warm Period. TheMedieval Warm Period likely occurred around 950-1100 AD in the NorthernHemisphere (Wikipedia, 2017). Evidence by paleo-climatic and model datasuggests that Medieval Warm Period (MWP) can be used to relate to thepossibility of similar distressed conditions in the future for California. (Woodhouse,2009) Extreme weather is increasing in the hotter world of global warming.
As2016 was the warmest year on record (lecture 3, slide 39), it had a directimpact on the increasing of drought and other extreme events. We can measure today’s drought by the PalmerDrought Severity Index or PDSI. This index “determines long-time drought especiallyover low and middle latitude” (Dai, Aiguo, 2017). It also cares for the pastconditions that are related to climate changes and evapotranspiration. IsCalifornia’s climate in 2018 going to be dry? Are we going for another state ofemergency this year? How would a really wet or dry 2018 affect the trends? CanCalifornia’s residents begin to not worry too much about their water usageagain? Method:PDSI has beenpreviously described as a measure to estimate relative dryness. This method iscalculated to “capture the basic effect of global warming on drought throughchanges in potential evapotranspiration”. (National Center for AtmosphericResearch Staff, 2017).
Severe drought isclassified as -3 and extreme drought in as -4 on the PDSI scale. At the otherend, very moist is >3 and extremely moist is >4. Values below -4 areextremely rare in the US. Regression with positive slope would indicateincreasing wetness of the California weather and a new climate.
The oppositeholds for negative slope, a trend of drier years and continued drought. Results. The data in Figure 1 on page the last page shows thatwithin the last 122 years the PDSI values are generally slowly decreasing.
Italso shows how between 2010-2015 there was severe/extreme drought and in 2016there was enough rain for the State of California to be very moist. The trendin the linear line is negative and the p-values are greater than 0.05. The linealso has a slope that is not equal to zero which means that the regression lineis not statistically significant.
The LOWESS lines are also decreasing at f=1and f=0.5. It is hard to indicate if California is out of the drought at thistime. Discussion: The Medieval warm period is a period that a lot of peoplewould consider when discussing global warming. “The causes of past andfuture drought will not be identical but warm droughts, inferred from paleo-climaticrecords, demonstrate the plausibility of extensive, severe droughts, provide along-term perspective on the ongoing drought conditions in the Southwest, andsuggest the need for regional sustainability planning for the future.”(Woodhouse,2009).
Evidence of this extensive droughtin medieval years is also seen in stumps found in the Sierra Nevada lakes.Until these stumps were located, the “Dust Bowl Period” which happened from1928 until 1934 was considered the worst drought documented. The stumps werediscovered at the base of four lakes in the Sierra Nevada: Osgood Swamp, MonoLake, Tenaya Lake, and the West Walker River. These stumps show that thesebodies of water fell to extremely low levels a few times because of the lingeringdrought (Stine, 1994).
Moreover, Jay Lund describesCalifornia’s drought as persistent. He claims that the dry December a lot oftimes means a drier year. He emphasizes that according to the historical statisticsof monthly precipitation in Northern California, maybe 2018 will be drier thanthe median and drier than average. (Lund: 2017). He also claims that there is areally small chance of flooding in the State but officials should not beskeptical of it happening.