Introduction

Hawaii has experienced agricultural land use change from 1980 to 2015, a shift from the plantation era in sugar and pineapple production to growing more diversified crops (State of Hawaii 2016). Agriculture, closely tied to and usually clustered around water sources, uses one-third of all water withdrawn in the US every day (US EPA 2015). In this project, I mapped agricultural land use (1976) and watersheds (2017) in Hawaii main islands (Figure 1) and provided zoomed views to subgroups of islands.

Figure 1: Hawaii main islands. Image download from mother’s niche.

Data Source

The land use/cover and watersheds data are downloaded from Hawaii Statewide GIS Program. I filtered out agricultural landcover types and renamed Horticultural Areas to represent Orchards, Groves, Vineyards, Nurseries and Ornamental Horticultural Areas.

Maps

#attach packages

library(sf)
library(tmap)
library(tidyverse)
library(here)
library(paletteer)
library(patchwork)
# read in data

hw_land_use <- read_sf(dsn = here("data", "land_use_land_cover_lulc"), layer = "Land_Use_Land_Cover_LULC") 

hw_water <- read_sf(dsn = here("data", "watersheds_HW"), layer = "Watersheds")
# check crs
st_crs(hw_land_use) 
st_crs(hw_water) 
# both CRS: EPSG: 4326
# filter agricultural lands
hw_agr_hrti_range_land <- hw_land_use %>% 
  filter(landcover %in% c("Cropland and Pasture", "Orchards, Groves, Vineyards, Nurseries and Ornamental Horticultural Areas", "Other Agricultural Land", "Confined Feeding Operations"))

# rename "Orchards, Groves, Vineyards, Nurseries and Ornamental Horticultural Areas" to "Horticultural Areas"
hw_agr_hrti_range_land$landcover[hw_agr_hrti_range_land$landcover == "Orchards, Groves, Vineyards, Nurseries and Ornamental Horticultural Areas"] = "Horticultural Areas"

Overall maps

Cropland and pasture dominate the agricultural land use in Hawaii in 1976 (Figure 2). Agricultural lands tend to be created near the shore where most watersheds were branched and clustered.

# plot overall agricultural land in Hawaii
hw_agr_all <- ggplot(data = hw_water) +
  geom_sf(color = NA,
          fill = "gray90",
          size = 0.06,
          alpha = 0.6) +
  geom_sf(data = hw_agr_hrti_range_land,
          aes(fill = landcover),
          color = NA) +
  theme_bw() +
  labs(caption = "Agricultural land in Hawaii",
       fill = " ") +
  scale_fill_manual(values = c("darkorange1", "seagreen", "palevioletred2", "purple3"))

# plot overall watershed in Hawaii
hw_water_all <- ggplot(data = hw_water) +
  geom_sf(aes(color = area_sqmi),
          fill = "white",
          size = 0.3,
          alpha = 0.5) +
  theme_bw() +
  labs(caption = "Watersheds in Hawaii",
       color = "Area (mile^2)") +
  scale_color_paletteer_c(palette = "grDevices::Blues 3",
                          direction = -1) 

# plot in a patch
hw_agr_all /
  hw_water_all

Figure 2: Agricultural land use and watersheds in Hawaii. Overall, most watersheds in Hawaii have area less than 5 square miles (light blue in lower map). Also, agricultural land use was significantly dominated by cropland (green in upper map) and pasture, where the former was largely used to produce sugar in 1976. Data source: Hawaii Statewide GIS Program.

Look at each island

Land use for agriculture varied among each islands.

# make a overall map, combining agricultural land use and watersheds
hw_all <- ggplot(data = hw_water)  +
  geom_sf(data = hw_agr_hrti_range_land,
          aes(fill = landcover),
          color = NA) +
  geom_sf(aes(color = area_sqmi),
          fill = NA,
          size = 0.25,
          alpha = 0.3) +
  theme_bw() +
  labs(caption = "Agricultural land use and watersheds in Hawaii",
       fill = " ",
       color = "Area (mile^2)") +
  scale_color_paletteer_c(palette = "grDevices::Blues 3",
                          direction = -1) +
  scale_fill_manual(values = c("darkorange1", "seagreen", "palevioletred2", "purple3"))

# adjust coordinates to the islands groups
hw_large_island <- hw_all +
  coord_sf(xlim = c(-156.3, -154.6),
           ylim = c(18.8, 20.4)) +
  labs(title = "Hawaii Island")

hw_middle_right_island <- hw_all +
  coord_sf(xlim = c(-157.5, -155.8),
           ylim = c(20.4, 21.3)) +
  labs(title = "Molokai, Maui, Kahoolawe, and Lanai Islands") 

hw_middle_left_island <- hw_all +
  coord_sf(xlim = c(-158.4, -157.6),
           ylim = c(21.2, 21.8)) +
  labs(title = "Oahu Island") 

hw_upper_island <- hw_all +
  coord_sf(xlim = c(-160.4, -159.2),
           ylim = c(21.7, 22.3)) +
  labs(title = "Kauai and Niihau Islands") 
hw_large_island

Figure 2: Agricultural land use and watersheds in Hawaii Island. Land use is dominated by cropland and pasture. Horticultural areas also presented near cropland and pasture. Most agricultural lands clustered in the north side of the island where most watersheds were found. Data source: Hawaii Statewide GIS Program.

hw_middle_right_island

Figure 3: Agricultural land use and watersheds in Molokai, Maui, Kahoolawe, and Lanai Islands. Land use is dominated by cropland and pasture. Horticultural areas also presented in Maui island but was very limited in size. No land use for agriculture in Kahoolawe. Data source: Hawaii Statewide GIS Program.

hw_middle_left_island

Figure 4: Agricultural land use and watersheds in Oahu Islands. Land use is also dominated by cropland and pasture. The other three types of area (confined feeding operations, horticultural areas, and other agricultural land) were also presented but were very small in size. Data source: Hawaii Statewide GIS Program.

hw_upper_island

Figure 5: Agricultural land use and watersheds in Kauai and Niihau Islands. Land use in Kauai island is dominated by cropland and pasture while horticultural areas presented in both islands. Data source: Hawaii Statewide GIS Program.

Options to view it interactively

To get a even closer look at the agricultural land use, please explore the interactive maps below! Note: the colors in the maps below are different from the static maps above.

# set to interactive mode
tmap_mode("view")

# select only landcover data to appear when clicking on map
hw_agr_hrti_range_land_plot <- hw_agr_hrti_range_land %>% 
  select(landcover)

tm_shape(hw_agr_hrti_range_land_plot) +
  tm_fill("landcover", 
          palette = "-Dark2",
          alpha = 0.8,
          title = "Agricultural land use in Hawaii") +
  tm_basemap("Esri.WorldTerrain") 
# select only watershed names and areas data to appear when clicking on map
hw_water_sub <- hw_water %>% 
  select(wuname, area_sqmi) %>% 
  rename("Watershed unit name" = wuname,
         "Area of watershed (mile^2)" = area_sqmi)
tm_shape(hw_water_sub) +
  tm_polygons(alpha = 0.1) +
  tm_basemap("Esri.WorldTerrain")

Reference

State of Hawaii, Department of Agriculture. 2016, February 17. Hawaii Agricultural Land Use Study Released. https://hdoa.hawaii.gov/blog/main/nrsalus2015/.

US EPA, OECA. 2015, August 17. Agriculture and Land Use. Overviews and Factsheets. https://www.epa.gov/agriculture/agriculture-and-land-use.