Use mod16 to investigate yearly variability in ET
Step 1: import the mod16 image collection
Step 2: Set the date variables
// set start and end year var startyear = 2000; var endyear = 2014; // make a date object var startdate = ee.Date.fromYMD(startyear, 1, 1); var enddate = ee.Date.fromYMD(endyear + 1, 1, 1); // make a list with years var years = ee.List.sequence(startyear, endyear);
Step 3: Set the geographic location
// Specify Country names var country_names = ['Indonesia']; // Get the country boundaries var countries = ee.FeatureCollection('ft:1tdSwUL7MVpOauSgRzqVTOwdfy17KDbw-1d9omPw'); // Filter for country var Indonesia = countries.filter(ee.Filter.inList('Country', country_names)); // Get the geometry var Indonesia = Indonesia.geometry(); // Get ET var ET = mod16.select("ET")
Step 4: Calculate the yearly ET
var annualET = ee.ImageCollection.fromImages( years.map(function (year) { var annual = ET .filter(ee.Filter.calendarRange(year, year, 'year')) .sum() .multiply(0.1); return annual .set('year', year) .set('system:time_start', ee.Date.fromYMD(year, 1, 1)); }));
Step 5: Make a chart of the data
var title = { title: 'Annual ET', hAxis: {title: 'Time'}, vAxis: {title: 'ET (mm)'}, }; var chart = ui.Chart.image.seriesByRegion({ imageCollection: annualET, regions: Indonesia, reducer: ee.Reducer.mean(), band: 'ET', scale: 2500, xProperty: 'system:time_start', seriesProperty: 'SITE' }).setOptions(title) .setChartType('ColumnChart'); print(chart);
Step 6: Calculate the mean of the period
var annualMean = annualET.mean().clip(Indonesia);
Step 7: show the map
var ETViz = { min: 1200, max: 1800, palette: '000000, 0000FF, FDFF92, FF2700, FF00E7' }; Map.centerObject(Indonesia, 5); Map.addLayer(annualMean,ETViz, 'mean yearly ET');
See an example here.