Weather measures current conditions such astemperature, moisture and wind while climate measures those for a long periodfor a certain area. Nowadays, climate is undergoing a major change. California hasa Mediterranean climate. “Mediterranean climates have most precipitation inwinter when temperatures are low” (Lecture 2 slide 65). In 2014, the mayor of Californiadeclared a state emergency of drought. Drought comes when winter rains are lessthan average and when summers are hotter than average.
The drought from 2010-2015was not the worst in California’s history as the state had 150 years of droughtduring the Medieval Warm Period. The Medieval Warm Period likely occurred around950-1100 AD in the Northern Hemisphere (Wikipedia, 2017). Evidence by paleo-climaticand model data suggests that Medieval Warm Period (MWP) can be used to relateto the possibility of similar distressed conditions in the future forCalifornia. (Woodhouse, 2009) Extreme weather is increasing in the hotter worldof global warming. As 2016 was the warmest year on record (lecture 3, slide39), it had a direct impact on the increasing of drought and other extremeevents. Woodhouse also emphasize that droughts are directly affected byelevated temperatures “because of factors such as subsidence, a lack of cloudcover, drying soils, and reduced evapotranspiration” (Woodhouse,2009). We can measure today’s droughtby the Palmer Drought Severity Index or PDSI.
This index “determines long-timedrought especially over low and middle latitude” (Dai, Aiguo, 2017). It alsocares 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 stateof 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 usageagain? Has drought changed in this year so far? What are some of the short andlong-term perspectives for the weather and Climate in California? Method:PDSIhas been previously described as a measure to estimate relative dryness. Thismethod is calculated to “capture the basic effect of global warming on droughtthrough changes in potential evapotranspiration”.
(National Center forAtmospheric Research 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. I plotted the PDSI for California from 1895 through2017.
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Regression with positive slope would indicate increasing wetness of theCalifornia weather and a new climate. The opposite holds for negative slope, atrend of drier years and continued drought. Two types of regression wereprovided for this research: linear regression and LOWESS (Locally WeightedScatterplot Smoothing).
The local weighting places more weight locally andproduce a line that closely follows the ups and downs. LOWESS is non-parametric,and its data is not a result of any usual type of distribution. The weighingfactor is signified as “f.” Three values of f are given (1, 0.5, 0.1).
Thevalues of f that are larger are more like the linear regression with weakerlocal weights. The values of f that are smaller, place the weight more locallyand are more of a curvy line that follows the values more closely. (problem set1,2018) Results. The data in Figure 1 on thelast page shows that in the period of the last 122 years the PDSI values aregenerally decreasing at a steady pace. It also shows how between 2010-2015there was severe/extreme drought and in 2016 there was enough rain for theState of California to be very moist. The trend in the linear line is negativeand the p-values are greater than 0.05.
The line also has a slope that is notequal to zero which means that the regression line is not statisticallysignificant. The LOWESS lines are also decreasing at f=1 and f=0.5. It is hardto indicate if California is out of the drought at this time even after areally wet year of 2017. For the value of a dry 2018, I substituted a severedry year which had a PDSI of -3.
1 the p-value was: 0.0131. For the value of a wet2018, I substituted a really wet year which had a PDSI of 4.5 and the p-value:0.0637. The Palmer Index severity is -2.
29 (according to the problemset 1, thisis that far away from real drought) Discussion:The Medieval warm period isa period that a lot of people would consider when discussing global warming. “The causes of past and futuredrought 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,and suggest the need for regional sustainability planning for the future.”(Woodhouse,2009). The last 122 years of drought arestill not erased even with the wet year of 2017 or as one my friends liked tocall it “El Nino year”.
So far it is not promising for the area of Yolo Countyas the Palmer Index (according to NOAA) is still in moderate drought. This isshown in figure 3 in the last page. I know this is not much of an indicator butit might show how we are still in winter and haven’t received much rain as lastyear.Evidence of this extensive drought in medieval years is alsoseen in stumps found in the Sierra Nevada lakes. Until these stumps werelocated, the “Dust Bowl Period” which happened from 1928 until 1934 wasconsidered the worst drought documented.
The stumps were discovered at the baseof four lakes in the Sierra Nevada: Osgood Swamp, Mono Lake, Tenaya Lake, and theWest Walker River. These stumps show that these bodies of water fell toextremely low levels a few times because of the lingering drought (Stine,1994).Moreover, Jay Lund describes California’s drought aspersistent.
He claims that the dry December a lot of times means a drier year.He emphasizes that according to the historical statistics of monthly precipitationin Northern California, maybe 2018 will be drier than the median and drier thanaverage. (Lund: 2017). He also claims that there is a really small chance offlooding in the State but officials should not be skeptical of it happening. Also, when comparingthe values of the p-value for hypothetical wet and dry 2018, the evidencesuggests there is a very high chance for drier 2018 because the p-value is lessthan 0.05 (0.0131) and that having a wet year has a really small chance sincethe p-value is higher than 0.
05 (0.0637). with these data, it can be said thatCalifornia is technically still in a drought.We should be careful as the early wet period of 2017 turnedinto increased fuel for wildfires during the dry part of 2017. This is what Dr.Stine has suggested in his paper.
He showed how hydro-climatic shifts fromexcessive dryness to extreme wetness and back to dryness would increase the recurrenceof extreme drought. These abruptions are definitely affected by the increase inglobal warming. Woodhouse has suggested there is a link between global warmingand Hadley cells (which are “large scale circulation patterns resulting fromuplift in the tropics”) (Lecture 2, slide 16). Since California is in atemperate zone that has wet winters and very long dry summers. We are going to experiencea high wave of dry temperature soon.
Woodhouse also claims that “global warmingis an extension of the poleward arm of the Hadley cell that will cause anexpansion of the area under the drying influence of subtropical high pressure”(Woodhouse,2009). He also claims that these results of Hadley cells are notfavored for drought-inducing circulations. I do disagree with him simplybecause for example, Davis ~ 38.
5o North has not had that much of rain for thisyear especially in a month that is supposed to be very wet (December). Myassessment is that the weather for this year in California would be drier butthe rain that fall on 2017 still will make the state not in a panic mood forthis year. Prolonged shortages in the water supply however might be affectedsince the conditions nowadays are similar to the one Stine is suggesting mightbe the reason for the stumps in Sierra Lake. The medieval drought could providea link between hemispheric warming and the generation of prolonged aridity. Accordingto Stevens, California ended its prolonged drought with much of its Folsom lakereservoir reduced to more than its third capacity and most of the Sierra Nevadasnowpack eliminated.
(Stevens, 2017) Californians must continue to cut theirwater consumption since the next drought is not going to be so far awayaccording to this year’s winter/rainfall record as illustrated by Jay Lundclaim that “California almost has to have at least two dry years together for thereto be a noteworthy drought” (Lund,2017). Yes we do have enough reservoir andaquifer storage but we should not making the mistakes of past years because itdoes not look promising for this year so far. If the history of the planet is any indicator of the future,our climate increase in the emissions of carbon dioxide, Chlorofluorocarbons,and other greenhouse gases along with the increasing occurrence of extremeevents such as drought will affect the state of California with more ecosystemdamage such as alteration of the Earth’s energy balance and decreases in theamount of energy that leaves the atmosphere. To conclude, California is verydependent on the amount of water precipitation and therefore we should be awareof what the data from the regression lines suggest and how we are going toimprove our management in handling the water supply and how we can lessen thedamage inflicted by the anthropogenic activities and other substantial weathercatastrophes.
