1 Mini-Challenge

#create two objects: tornadoes before 2000 and tornadoes after 2000
torn_before_2000 <- torn |> filter(yr < 2000)
torn_after_2000 <- torn |> filter(yr >= 2000)

#calculate the weighted mean center (weighted by mag) for each time period
torn_w_mean_center_before <- center_mean(torn_before_2000, weight = torn_before_2000$mag)
torn_w_mean_center_after <- center_mean(torn_after_2000, weight = torn_after_2000$mag)

#map the two weighted mean centers together
tm_shape(torn) + tm_dots() +
  tm_shape(torn_w_mean_center_before) + tm_dots(fill = "blue") +
  tm_shape(torn_w_mean_center_after) + tm_dots(fill = "red") +
  tm_add_legend(
    type = "symbols",
    labels = c("Weighted Mean Center (Pre-2000)", "Weighted Mean Center (Post-2000)"),
    fill = c("blue", "red")
  )

#look at the actual coordinates to describe the shift precisely
torn_w_mean_center_before
## Geometry set for 1 feature 
## Geometry type: POINT
## Dimension:     XY
## Bounding box:  xmin: 372822.8 ymin: 1594581 xmax: 372822.8 ymax: 1594581
## Projected CRS: NAD83 / Conus Albers
torn_w_mean_center_after 
## Geometry set for 1 feature 
## Geometry type: POINT
## Dimension:     XY
## Bounding box:  xmin: 488989.9 ymin: 1570309 xmax: 488989.9 ymax: 1570309
## Projected CRS: NAD83 / Conus Albers

1.1 Determine what this difference tells us about how the spatial pattern of tornadoes has changed over time.

The weighted mean center of higher-magnitude tornadoes shifted about 74 miles eastward and slighly southward between the pre-2000 and post-2000 periods. This suggests that the geographic core of severe tornado activity has drifted somewhat away from the traditional “Tornado Alley” of the Great Plains toward the Mid-South/Southeast. This is sometimes attributed to the shifting atmospheric moisture and wind shear patterns possibly linked to climate change.