This script charts the mean Normalized Difference Vegetation Index (NDVI) using the MODIS data collection for the period of June 1-15 from 2000 to 2019 within generalized calving areas of the Western Arctic Herd, Teshekpuk Herd, Central Arctic Herd, and Porcupine Herd. This script was created as an example of wildlife-related applications of Goo…

calving_ndvi_trends.js

/* -*- coding: utf-8 -*-
---------------------------------------------------------------------------
Summary Chart of NDVI Trends in Calving Grounds for Four Arctic Caribou Herds
Author: Timm Nawrocki, Alaska Center for Conservation Science
Last Updated: 2020-02-05
Usage: Must be executed from the Google Earth Engine code editor.
Description: This script charts the mean Normalized Difference Vegetation Index (NDVI) using
the MODIS data collection for the period of June 1-15 from 2000 to 2019 within generalized
calving areas of the Western Arctic Herd, Teshekpuk Herd, Central Arctic Herd, and Porcupine
Herd. This script was created as an example of wildlife-related applications of Google Earth
Engine in Alaska.
---------------------------------------------------------------------------*/

// Define the calving areas
var calving_central = ee.FeatureCollection("users/twnawrocki/CentralCalvingRange")
  .first()
  .geometry();
var calving_porcupine = ee.FeatureCollection("users/twnawrocki/PorcupineCalvingRange")
  .first()
  .geometry();
var calving_teshekpuk = ee.FeatureCollection("users/twnawrocki/TeshekpukCalvingRange")
  .first()
  .geometry();
var calving_western = ee.FeatureCollection("users/twnawrocki/WesternCalvingRange")
  .first()
  .geometry();

// Define new feature collection that includes all herds
var regions = ee.FeatureCollection([
  ee.Feature(calving_western, {label: 'Western Arctic Herd'}),
  ee.Feature(calving_teshekpuk, {label: 'Teshekpuk Herd'}),
  ee.Feature(calving_central, {label: 'Central Arctic Herd'}),
  ee.Feature(calving_porcupine, {label: 'Porcupine Herd'})
]);

// Define the MODIS image collection
var collection = ee.ImageCollection('MODIS/006/MOD13Q1');
print('Image Collection: ', collection);

// Filter the collection to specific dates
var collection_june = collection.filter(
  ee.Filter.calendarRange(152, 166, 'day_of_year')
);

// Visualize NDVI for 2019
var dataset = collection_june.filter(
  ee.Filter.calendarRange(2019, 2019, 'year')
);
var ndvi = dataset.select('NDVI');
var ndviVis = {
  min: 0.0,
  max: 10000.0,
  palette: [
    'FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901',
    '66A000', '529400', '3E8601', '207401', '056201', '004C00', '023B01',
    '012E01', '011D01', '011301'
  ],
};
Map.setCenter(-153, 69.5, 6);
Map.addLayer(ndvi, ndviVis, 'NDVI');
Map.addLayer(regions);

// Create and print chart for NDVI over time for four herds
var herds_chart = ui.Chart.image.seriesByRegion(
  collection_june,
  regions,
  ee.Reducer.mean(),
  'NDVI',
  100, // Reduce Scale
  'system:time_start',
  'label')
    .setOptions({
      title: 'Trend of early June mean NDVI per year for four arctic caribou herds from 2000 to 2019',
      vAxis: {title: 'Mean Early June NDVI'},
      hAxis: {title: 'Year'},
      lineWidth: 2,
      pointSize: 4,
      series: {
        0: {color: '00429D'}, // Western Arctic Herd
        1: {color: '73A2C6'}, // Teshekpuk Herd
        2: {color: 'F4777F'}, // Central Arctic Herd
        3: {color: '93003A'} // Porcupine Herd
      }
    }
  );
  
// Display chart
print(herds_chart);