Impact of Severe Weather Events on Public Health and Economy in the United States

Synonpsis

In this report, we aim to analyze the impact of different weather events on public health and economy based on the storm database collected from the U.S. National Oceanic and Atmospheric Administration’s (NOAA) from 1950 - 2011. We will use the estimates of fatalities, injuries, property and crop damage to decide which types of event are most harmful to the population health and economy. From these data, we found that excessive heat and tornado are most harmful with respect to population health, while flood, drought, and hurricane/typhoon have the greatest economic consequences.

Loading required packages

library(R.utils)
## Loading required package: R.oo
## Loading required package: R.methodsS3
## R.methodsS3 v1.7.1 (2016-02-15) successfully loaded. See ?R.methodsS3 for help.
## Registered S3 method overwritten by 'R.oo':
##   method        from       
##   throw.default R.methodsS3
## R.oo v1.22.0 (2018-04-21) successfully loaded. See ?R.oo for help.
## 
## Attaching package: 'R.oo'
## The following objects are masked from 'package:methods':
## 
##     getClasses, getMethods
## The following objects are masked from 'package:base':
## 
##     attach, detach, gc, load, save
## R.utils v2.9.0 successfully loaded. See ?R.utils for help.
## 
## Attaching package: 'R.utils'
## The following object is masked from 'package:utils':
## 
##     timestamp
## The following objects are masked from 'package:base':
## 
##     cat, commandArgs, getOption, inherits, isOpen, nullfile,
##     parse, warnings
library(ggplot2)
## Registered S3 methods overwritten by 'ggplot2':
##   method         from 
##   [.quosures     rlang
##   c.quosures     rlang
##   print.quosures rlang
library(plyr)
require(gridExtra)
## Loading required package: gridExtra

Loading the NOAA Storm Data

Before running this code download the data from this link “http://d396qusza40orc.cloudfront.net/repdata%2Fdata%2FStormData.csv.bz2”. Then proceed to unzip the file and save the unzipped file into your preferred location. Remember to replace the pathway to the unzipped csv file before trying to read in the NOAA Storm data.

NOAA <- read.csv("~/Coursera/repdata-data-StormData.csv")

There are 902297 rows and 37 columns in total. Also, the data starts in April of 1950 and ends in November of 2011.

dim(NOAA)
## [1] 902297     37
head(NOAA)
##   STATE__           BGN_DATE BGN_TIME TIME_ZONE COUNTY COUNTYNAME STATE
## 1       1  4/18/1950 0:00:00     0130       CST     97     MOBILE    AL
## 2       1  4/18/1950 0:00:00     0145       CST      3    BALDWIN    AL
## 3       1  2/20/1951 0:00:00     1600       CST     57    FAYETTE    AL
## 4       1   6/8/1951 0:00:00     0900       CST     89    MADISON    AL
## 5       1 11/15/1951 0:00:00     1500       CST     43    CULLMAN    AL
## 6       1 11/15/1951 0:00:00     2000       CST     77 LAUDERDALE    AL
##    EVTYPE BGN_RANGE BGN_AZI BGN_LOCATI END_DATE END_TIME COUNTY_END
## 1 TORNADO         0                                               0
## 2 TORNADO         0                                               0
## 3 TORNADO         0                                               0
## 4 TORNADO         0                                               0
## 5 TORNADO         0                                               0
## 6 TORNADO         0                                               0
##   COUNTYENDN END_RANGE END_AZI END_LOCATI LENGTH WIDTH F MAG FATALITIES
## 1         NA         0                      14.0   100 3   0          0
## 2         NA         0                       2.0   150 2   0          0
## 3         NA         0                       0.1   123 2   0          0
## 4         NA         0                       0.0   100 2   0          0
## 5         NA         0                       0.0   150 2   0          0
## 6         NA         0                       1.5   177 2   0          0
##   INJURIES PROPDMG PROPDMGEXP CROPDMG CROPDMGEXP WFO STATEOFFIC ZONENAMES
## 1       15    25.0          K       0                                    
## 2        0     2.5          K       0                                    
## 3        2    25.0          K       0                                    
## 4        2     2.5          K       0                                    
## 5        2     2.5          K       0                                    
## 6        6     2.5          K       0                                    
##   LATITUDE LONGITUDE LATITUDE_E LONGITUDE_ REMARKS REFNUM
## 1     3040      8812       3051       8806              1
## 2     3042      8755          0          0              2
## 3     3340      8742          0          0              3
## 4     3458      8626          0          0              4
## 5     3412      8642          0          0              5
## 6     3450      8748          0          0              6
tail(NOAA)
##        STATE__           BGN_DATE    BGN_TIME TIME_ZONE COUNTY
## 902292      47 11/28/2011 0:00:00 03:00:00 PM       CST     21
## 902293      56 11/30/2011 0:00:00 10:30:00 PM       MST      7
## 902294      30 11/10/2011 0:00:00 02:48:00 PM       MST      9
## 902295       2  11/8/2011 0:00:00 02:58:00 PM       AKS    213
## 902296       2  11/9/2011 0:00:00 10:21:00 AM       AKS    202
## 902297       1 11/28/2011 0:00:00 08:00:00 PM       CST      6
##                                  COUNTYNAME STATE         EVTYPE BGN_RANGE
## 902292 TNZ001>004 - 019>021 - 048>055 - 088    TN WINTER WEATHER         0
## 902293                         WYZ007 - 017    WY      HIGH WIND         0
## 902294                         MTZ009 - 010    MT      HIGH WIND         0
## 902295                               AKZ213    AK      HIGH WIND         0
## 902296                               AKZ202    AK       BLIZZARD         0
## 902297                               ALZ006    AL     HEAVY SNOW         0
##        BGN_AZI BGN_LOCATI           END_DATE    END_TIME COUNTY_END
## 902292                    11/29/2011 0:00:00 12:00:00 PM          0
## 902293                    11/30/2011 0:00:00 10:30:00 PM          0
## 902294                    11/10/2011 0:00:00 02:48:00 PM          0
## 902295                     11/9/2011 0:00:00 01:15:00 PM          0
## 902296                     11/9/2011 0:00:00 05:00:00 PM          0
## 902297                    11/29/2011 0:00:00 04:00:00 AM          0
##        COUNTYENDN END_RANGE END_AZI END_LOCATI LENGTH WIDTH  F MAG
## 902292         NA         0                         0     0 NA   0
## 902293         NA         0                         0     0 NA  66
## 902294         NA         0                         0     0 NA  52
## 902295         NA         0                         0     0 NA  81
## 902296         NA         0                         0     0 NA   0
## 902297         NA         0                         0     0 NA   0
##        FATALITIES INJURIES PROPDMG PROPDMGEXP CROPDMG CROPDMGEXP WFO
## 902292          0        0       0          K       0          K MEG
## 902293          0        0       0          K       0          K RIW
## 902294          0        0       0          K       0          K TFX
## 902295          0        0       0          K       0          K AFG
## 902296          0        0       0          K       0          K AFG
## 902297          0        0       0          K       0          K HUN
##                       STATEOFFIC
## 902292           TENNESSEE, West
## 902293 WYOMING, Central and West
## 902294          MONTANA, Central
## 902295          ALASKA, Northern
## 902296          ALASKA, Northern
## 902297            ALABAMA, North
##                                                                                                                                                            ZONENAMES
## 902292 LAKE - LAKE - OBION - WEAKLEY - HENRY - DYER - GIBSON - CARROLL - LAUDERDALE - TIPTON - HAYWOOD - CROCKETT - MADISON - CHESTER - HENDERSON - DECATUR - SHELBY
## 902293                                                                              OWL CREEK & BRIDGER MOUNTAINS - OWL CREEK & BRIDGER MOUNTAINS - WIND RIVER BASIN
## 902294                                                                                     NORTH ROCKY MOUNTAIN FRONT - NORTH ROCKY MOUNTAIN FRONT - EASTERN GLACIER
## 902295                                                                                                 ST LAWRENCE IS. BERING STRAIT - ST LAWRENCE IS. BERING STRAIT
## 902296                                                                                                                 NORTHERN ARCTIC COAST - NORTHERN ARCTIC COAST
## 902297                                                                                                                                             MADISON - MADISON
##        LATITUDE LONGITUDE LATITUDE_E LONGITUDE_
## 902292        0         0          0          0
## 902293        0         0          0          0
## 902294        0         0          0          0
## 902295        0         0          0          0
## 902296        0         0          0          0
## 902297        0         0          0          0
##                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        REMARKS
## 902292                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    EPISODE NARRATIVE: A powerful upper level low pressure system brought snow to portions of Northeast Arkansas, the Missouri Bootheel, West Tennessee and extreme north Mississippi. Most areas picked up between 1 and 3 inches of with areas of Northeast Arkansas and the Missouri Bootheel receiving between 4 and 6 inches of snow.EVENT NARRATIVE: Around 1 inch of snow fell in Carroll County.
## 902293                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           EPISODE NARRATIVE: A strong cold front moved south through north central Wyoming bringing high wind to the Meeteetse area and along the south slopes of the western Owl Creek Range. Wind gusts to 76 mph were recorded at Madden Reservoir.EVENT NARRATIVE: 
## 902294                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      EPISODE NARRATIVE: A strong westerly flow aloft produced gusty winds at the surface along the Rocky Mountain front and over the plains of Central Montana. Wind gusts in excess of 60 mph were reported.EVENT NARRATIVE: A wind gust to 60 mph was reported at East Glacier Park 1ENE (the Two Medicine DOT site).
## 902295 EPISODE NARRATIVE: A 960 mb low over the southern Aleutians at 0300AKST on the 8th intensified to 945 mb near the Gulf of Anadyr by 2100AKST on the 8th. The low crossed the Chukotsk Peninsula as a 956 mb low at 0900AKST on the 9th, and moved into the southern Chukchi Sea as a 958 mb low by 2100AKST on the 9th. The low then tracked to the northwest and weakened to 975 mb about 150 miles north of Wrangel Island by 1500AKST on the 10th. The storm was one of the strongest storms to impact the west coast of Alaska since November 1974. \n\nZone 201: Blizzard conditions were observed at Wainwright from approximately 1153AKST through 1611AKST on the 9th. The visibility was frequently reduced to one quarter mile in snow and blowing snow. There was a peak wind gust to 43kt (50 mph) at the Wainwright ASOS. During this event, there was also a peak wind gust to \n68 kt (78 mph) at the Cape Lisburne AWOS. \n\nZone 202: Blizzard conditions were observed at Barrow from approximately 1021AKST through 1700AKST on the 9th. The visibility was frequently reduced to one quarter mile or less in blowing snow. There was a peak wind gust to 46 kt (53 mph) at the Barrow ASOS. \n\nZone 207: Blizzard conditions were observed at Kivalina from approximately 0400AKST through 1230AKST on the 9th. The visibility was frequently reduced to one quarter of a mile in snow and blowing snow. There was a peak wind gust to 61 kt (70 mph) at the Kivalina ASOS.  The doors to the village transportation shed were blown out to sea.  Many homes lost portions of their tin roofing, and satellite dishes were ripped off of roofs. One home had its door blown off.  At Point Hope, severe blizzard conditions were observed. There was a peak wind gust of 68 kt (78 mph) at the Point Hope AWOS before power was lost to the AWOS. It was estimated that the wind gusted as high as 85 mph in the village during the height of the storm during the morning and early afternoon hours on the 9th. Five power poles were knocked down in the storm EVENT NARRATIVE: 
## 902296 EPISODE NARRATIVE: A 960 mb low over the southern Aleutians at 0300AKST on the 8th intensified to 945 mb near the Gulf of Anadyr by 2100AKST on the 8th. The low crossed the Chukotsk Peninsula as a 956 mb low at 0900AKST on the 9th, and moved into the southern Chukchi Sea as a 958 mb low by 2100AKST on the 9th. The low then tracked to the northwest and weakened to 975 mb about 150 miles north of Wrangel Island by 1500AKST on the 10th. The storm was one of the strongest storms to impact the west coast of Alaska since November 1974. \n\nZone 201: Blizzard conditions were observed at Wainwright from approximately 1153AKST through 1611AKST on the 9th. The visibility was frequently reduced to one quarter mile in snow and blowing snow. There was a peak wind gust to 43kt (50 mph) at the Wainwright ASOS. During this event, there was also a peak wind gust to \n68 kt (78 mph) at the Cape Lisburne AWOS. \n\nZone 202: Blizzard conditions were observed at Barrow from approximately 1021AKST through 1700AKST on the 9th. The visibility was frequently reduced to one quarter mile or less in blowing snow. There was a peak wind gust to 46 kt (53 mph) at the Barrow ASOS. \n\nZone 207: Blizzard conditions were observed at Kivalina from approximately 0400AKST through 1230AKST on the 9th. The visibility was frequently reduced to one quarter of a mile in snow and blowing snow. There was a peak wind gust to 61 kt (70 mph) at the Kivalina ASOS.  The doors to the village transportation shed were blown out to sea.  Many homes lost portions of their tin roofing, and satellite dishes were ripped off of roofs. One home had its door blown off.  At Point Hope, severe blizzard conditions were observed. There was a peak wind gust of 68 kt (78 mph) at the Point Hope AWOS before power was lost to the AWOS. It was estimated that the wind gusted as high as 85 mph in the village during the height of the storm during the morning and early afternoon hours on the 9th. Five power poles were knocked down in the storm EVENT NARRATIVE: 
## 902297                           EPISODE NARRATIVE: An intense upper level low developed on the 28th at the base of a highly amplified upper trough across the Great Lakes and Mississippi Valley.  The upper low closed off over the mid South and tracked northeast across the Tennessee Valley during the morning of the 29th.   A warm conveyor belt of heavy rainfall developed in advance of the low which dumped from around 2 to over 5 inches of rain across the eastern two thirds of north Alabama and middle Tennessee.  The highest rain amounts were recorded in Jackson and DeKalb Counties with 3 to 5 inches.  The rain fell over 24 to 36 hour period, with rainfall remaining light to moderate during most its duration.  The rainfall resulted in minor river flooding along the Little River, Big Wills Creek and Paint Rock.   A landslide occurred on Highway 35 just north of Section in Jackson County.  A driver was trapped in his vehicle, but was rescued unharmed.  Trees, boulders and debris blocked 100 to 250 yards of Highway 35.\n\nThe rain mixed with and changed to snow across north Alabama during the afternoon and  evening hours of the 28th, and lasted into the 29th.  The heaviest bursts of snow occurred in northwest Alabama during the afternoon and evening hours, and in north central and northeast Alabama during the overnight and morning hours.  Since ground temperatures were in the 50s, and air temperatures in valley areas only dropped into the mid 30s, most of the snowfall melted on impact with mostly trace amounts reported in valley locations.  However, above 1500 foot elevation, snow accumulations of 1 to 2 inches were reported.  The heaviest amount was 2.3 inches on Monte Sano Mountain, about 5 miles northeast of Huntsville.EVENT NARRATIVE: Snowfall accumulations of up to 2.3 inches were reported on the higher elevations of eastern Madison County.  A snow accumulation of 1.5 inches was reported 2.7 miles south of Gurley, while 2.3 inches was reported 3 miles east of Huntsville atop Monte Sano Mountain.
##        REFNUM
## 902292 902292
## 902293 902293
## 902294 902294
## 902295 902295
## 902296 902296
## 902297 902297
if (dim(NOAA)[2] == 37) {
    NOAA$year <- as.numeric(format(as.Date(NOAA$BGN_DATE, format = "%m/%d/%Y %H:%M:%S"), "%Y"))
}
hist(NOAA$year, breaks = 30, xlab = "Year", main = "Distribution of the NOAA Storm Data", col = "grey")

Based on the above histogram, we see that the number of events tracked starts to significantly increase around 1995. So, we use the subset of the data from 1995 to 2011 to get most out of good records.

After running the code below you should have 681500 rows and 38 columns in total.

storm <- NOAA[NOAA$year >= 1995,]
dim(storm)
## [1] 681500     38

Impact on Public Health

In this section, we check the number of fatalities and injuries that are caused by the severe weather events. We would like to get the first 15 most severe types of weather events.

sortHelp <- function(fieldName, top = 15, dataset = NOAA) {
    index <- which(colnames(dataset) == fieldName)
    field <- aggregate(dataset[, index], by = list(dataset$EVTYPE), FUN = "sum")
    names(field) <- c("EVTYPE", fieldName)
    field <- arrange(field, field[, 2], decreasing = T)
    field <- head(field, n = top)
    field <- within(field, EVTYPE <- factor(x = EVTYPE, levels = field$EVTYPE))
    return(field)
}
fatalities <- sortHelp("FATALITIES", dataset = storm)
injuries <- sortHelp("INJURIES", dataset = storm)

Impact on Economy

We will convert the property damage and crop damage data into comparable numerical forms according to the meaning of units described in the code book (Storm Events). Both PROPDMGEXP and CROPDMGEXP columns record a multiplier for each observation where we have Hundred (H), Thousand (K), Million (M) and Billion (B).

convertHelp <- function(dataset = storm, fieldName, newFieldName) {
    totalLen <- dim(dataset)[2]
    index <- which(colnames(dataset) == fieldName)
    dataset[, index] <- as.character(dataset[, index])
    logic <- !is.na(toupper(dataset[, index]))
    dataset[logic & toupper(dataset[, index]) == "B", index] <- "9"
    dataset[logic & toupper(dataset[, index]) == "M", index] <- "6"
    dataset[logic & toupper(dataset[, index]) == "K", index] <- "3"
    dataset[logic & toupper(dataset[, index]) == "H", index] <- "2"
    dataset[logic & toupper(dataset[, index]) == "", index] <- "0"
    dataset[, index] <- as.numeric(dataset[, index])
    dataset[is.na(dataset[, index]), index] <- 0
    dataset <- cbind(dataset, dataset[, index - 1] * 10^dataset[, index])
    names(dataset)[totalLen + 1] <- newFieldName
    return(dataset)
}
storm <- convertHelp(storm, "PROPDMGEXP", "propertyDamage")
## Warning in convertHelp(storm, "PROPDMGEXP", "propertyDamage"): NAs
## introduced by coercion
storm <- convertHelp(storm, "CROPDMGEXP", "cropDamage")
## Warning in convertHelp(storm, "CROPDMGEXP", "cropDamage"): NAs introduced
## by coercion
names(storm)
##  [1] "STATE__"        "BGN_DATE"       "BGN_TIME"       "TIME_ZONE"     
##  [5] "COUNTY"         "COUNTYNAME"     "STATE"          "EVTYPE"        
##  [9] "BGN_RANGE"      "BGN_AZI"        "BGN_LOCATI"     "END_DATE"      
## [13] "END_TIME"       "COUNTY_END"     "COUNTYENDN"     "END_RANGE"     
## [17] "END_AZI"        "END_LOCATI"     "LENGTH"         "WIDTH"         
## [21] "F"              "MAG"            "FATALITIES"     "INJURIES"      
## [25] "PROPDMG"        "PROPDMGEXP"     "CROPDMG"        "CROPDMGEXP"    
## [29] "WFO"            "STATEOFFIC"     "ZONENAMES"      "LATITUDE"      
## [33] "LONGITUDE"      "LATITUDE_E"     "LONGITUDE_"     "REMARKS"       
## [37] "REFNUM"         "year"           "propertyDamage" "cropDamage"
options(scipen=999)
property <- sortHelp("propertyDamage", dataset = storm)
crop <- sortHelp("cropDamage", dataset = storm)

Results

As for the impact on public health, we have got two sorted lists of severe weather events below by the number of people badly affected.

fatalities
##               EVTYPE FATALITIES
## 1     EXCESSIVE HEAT       1903
## 2            TORNADO       1545
## 3        FLASH FLOOD        934
## 4               HEAT        924
## 5          LIGHTNING        729
## 6              FLOOD        423
## 7        RIP CURRENT        360
## 8          HIGH WIND        241
## 9          TSTM WIND        241
## 10         AVALANCHE        223
## 11      RIP CURRENTS        204
## 12      WINTER STORM        195
## 13         HEAT WAVE        161
## 14 THUNDERSTORM WIND        131
## 15      EXTREME COLD        126
injuries
##               EVTYPE INJURIES
## 1            TORNADO    21765
## 2              FLOOD     6769
## 3     EXCESSIVE HEAT     6525
## 4          LIGHTNING     4631
## 5          TSTM WIND     3630
## 6               HEAT     2030
## 7        FLASH FLOOD     1734
## 8  THUNDERSTORM WIND     1426
## 9       WINTER STORM     1298
## 10 HURRICANE/TYPHOON     1275
## 11         HIGH WIND     1093
## 12              HAIL      916
## 13          WILDFIRE      911
## 14        HEAVY SNOW      751
## 15               FOG      718

And the following is a pair of graphs of total fatalities and total injuries affected by these severe weather events.

fatalitiesPlot <- ggplot(fatalities, aes(x = EVTYPE, y = FATALITIES)) + 
    geom_bar(stat = "identity") +
    scale_y_continuous("Number of Fatalities") + 
    theme(axis.text.x = element_text(angle = 45, 
    hjust = 1)) + xlab("Severe Weather Type") + 
    ggtitle("Total Fatalities by Severe Weather\n Events in the U.S.\n from 1995 - 2011")
injuriesPlot <- ggplot(injuries, aes(x = EVTYPE, y = INJURIES)) + 
    geom_bar(stat = "identity") +
    scale_y_continuous("Number of Injuries") + 
    theme(axis.text.x = element_text(angle = 45, 
    hjust = 1)) + xlab("Severe Weather Type") + 
    ggtitle("Total Injuries by Severe Weather\n Events in the U.S.\n from 1995 - 2011")
grid.arrange(fatalitiesPlot, injuriesPlot, ncol = 2)

Based on the above histograms, we find that excessive heat and tornado cause most fatalities; tornado causes most injuries in the United States from 1995 to 2011.

As for the impact on economy, we have got two sorted lists below by the amount of money cost by damages.

property
##               EVTYPE propertyDamage
## 1              FLOOD   144022037057
## 2  HURRICANE/TYPHOON    69305840000
## 3        STORM SURGE    43193536000
## 4            TORNADO    24935939545
## 5        FLASH FLOOD    16047794571
## 6               HAIL    15048722103
## 7          HURRICANE    11812819010
## 8     TROPICAL STORM     7653335550
## 9          HIGH WIND     5259785375
## 10          WILDFIRE     4759064000
## 11  STORM SURGE/TIDE     4641188000
## 12         TSTM WIND     4482361440
## 13         ICE STORM     3643555810
## 14 THUNDERSTORM WIND     3399282992
## 15    HURRICANE OPAL     3172846000
crop
##               EVTYPE  cropDamage
## 1            DROUGHT 13922066000
## 2              FLOOD  5422810400
## 3          HURRICANE  2741410000
## 4               HAIL  2614127070
## 5  HURRICANE/TYPHOON  2607872800
## 6        FLASH FLOOD  1343915000
## 7       EXTREME COLD  1292473000
## 8       FROST/FREEZE  1094086000
## 9         HEAVY RAIN   728399800
## 10    TROPICAL STORM   677836000
## 11         HIGH WIND   633561300
## 12         TSTM WIND   553947350
## 13    EXCESSIVE HEAT   492402000
## 14 THUNDERSTORM WIND   414354000
## 15              HEAT   401411500

And the following is a pair of graphs of total property damage and total crop damage affected by these severe weather events.

propertyPlot <- ggplot(property, aes(x = EVTYPE, y = propertyDamage)) + 
    geom_bar(stat = "identity") +
    theme(axis.text.x = element_text(angle = 45, hjust = 1)) + scale_y_continuous("Property Damage in US dollars")+ 
    xlab("Severe Weather Type") + ggtitle("Total Property Damage by\n Severe Weather Events in\n the U.S. from 1995 - 2011")
cropPlot<-ggplot(crop, aes(x = EVTYPE, y = cropDamage)) +
    geom_bar(stat = "identity") +
    theme(axis.text.x = element_text(angle = 45, hjust = 1)) + scale_y_continuous("Crop Damage in US dollars") + 
    xlab("Severe Weather Type") + ggtitle("Total Crop Damage by \nSevere Weather Events in\n the U.S. from 1995 - 2011")
grid.arrange(propertyPlot, cropPlot, ncol = 2)

Based on the above histograms, we find that flood and hurricane/typhoon cause most property damage; drought and flood causes most crop damage in the United States from 1995 to 2011.

Conclusion

From these data, we found that excessive heat and tornado are most harmful with respect to population health, while flood, drought, and hurricane/typhoon have the greatest economic consequences.