History of California Drought 1 The Palmer drought index, sometimes called the Palmer drought severity index and often abbreviated PDSI, is a measurement of soil moisture based on recent precipitation and temperature. It uses 0 as normal, and drought is shown in terms of negative numbers; for example, negative 2 is moderate drought, negative 3 is severe drought, and negative 4 is extreme drought. Graph 1: This graph shows drought severity and above average wetness. The data points are decade averages, with annual data reflected by the faint lines behind. Graph 2: This graph shows data over a smaller time span, making it easier to view annual PDSI values. It is also current.
Exercise 1 Graph Analysis 2 Instructions: Working with a partner, answer the questions below Sample answers in blue What is one limitation to graph 1? What is one limitation to graph 2? It ends at the year 2000 Hard to identify annual numbers Decade averages don t show peak wet or dry years clearly It does not show a lot of history You are a public policy planner in your town. Why might you want to have/use both graphs when preparing a report to the city council? Be prepared to share with the class!! We would use both to determine if short range trends reflect long range data Exercise 2 Map Analysis Instructions: Working with a partner, complete the activity to compare the maps to the Palmer Drought Severity Index. For each map, work with your partner to devise a system and place PDSI numbers in each colored region. Write the numbers on each map. Map 1: This map shows regional PDSI values. Instead of numbers, it uses gradations of color. It is a very common way public agencies use the PDSI
3 Exercise 3 Creating Your Own PDSI Map Instructions: Number each county with the correct/dominant PDSI Color each county according to its estimated average PDSI Color the key below the map (You will have to develop extra colors for values that fall between i.e. 3.5)
Color Key: 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5 4 Reference Map 1
Reference map 2 5
Reference map 3 6
7 Exercise 4 Analysis Questions Instructions: Analyze the graphs, maps, and your own work to answer these assessment questions in complete sentences. Sample answers are in blue 1What does the PDSI measure? 2Citing one of the sources, explain if and why you believe CA is in a state of drought 3Using Graph 2, develop a ratio of dry to wet years from 1902-21015 4Look at data for years 2004-2015. Use your ratio to predict if the drought should end, or continue. Explain your reasoning 5Take into consideration the data from graph 1. Why might it be dangerous to rely on data from such a narrow time frame (from graph 2) 6Infer: using reference map 2 and 3, explain how drought in the high elevation counties affects the water table in the central valley? 7In regards to well drilling regulations, what region(s) should scientists take into account when recommending groundwater use for the Central Valley agricultural communities? 8Thinking Back: Using The PDSI measures the amount of moisture in the soil based on precipitation and evaporation levels. According to graph 2, 8 of the last 10 years have experienced negative PDSI numbers. 6 have been below -2.5 PDSI, approaching extreme drought. Approximately 12:11 There have been 8 dry years to 4 wet years, a ratio of 2:1. Comparing that to the previous ration, I would predict that the drought should end. Graph one shows that California has experienced multiple droughts lasting over one hundred years. The data range from Graph two may not be enough data to accurately predict the nature of the current drought. California may be at the beginning of another mega drought. The higher elevations produce a snowpack that creates runoff to recharge the Central Valley aquifers. If they are dry, the valley receives less water in the summer. Scientists should monitor the amount of precipitation/weather/snowpack in the mountain areas to predict amount of recharge. We learned in the water competition lab that if use exceeds recharge, wells will
8 information from the Unfair Competition Lab, what may happen if Scientists recommendations are not taken into consideration? 9Go Further: Explore New. York Times Article (linked here): what evidence is presented that may indicate California s drought could continue to persist? run dry. According to the article, human caused climate change is intensifying the drought by 15-20 percent. Despite historical trends, the drought could continue.