Calculate monthly rainfall
Step 1: import the chirps data
Step 2: Set the date variables
// set start and end year var startyear = ??; var endyear = ??; // 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(??, ??);
Step 3: Set the geographic location
// Specify Country names var country_names = ['Sri Lanka']; // Get the country boundaries var countries = ee.FeatureCollection('ft:1tdSwUL7MVpOauSgRzqVTOwdfy17KDbw-1d9omPw'); // Filter for country var SriLanka = countries.filter(ee.Filter.inList('Country', country_names)); // Get the geometry var SriLanka = SriLanka.geometry();
Step 4:Calculate monthly precipitation
var monthlyPrecip = ee.ImageCollection.fromImages( years.map(function (y) { return months.map(function(m) { var w = chirps.filter(ee.Filter.calendarRange(y, y, 'year')) .filter(ee.Filter.calendarRange(m, m, 'month')) .sum(); return w.set('year', y) .set('month', m) .set('system:time_start', ee.Date.fromYMD(y, m, 1)); }); }).flatten() );
Step 5: Calculate monthly precipitation
var meanMonthlyP = ee.ImageCollection.fromImages( months.map(function (m) { var w = monthlyPrecip.filter(ee.Filter.eq('month', m)).??(); return w.set('month', m) .set('system:time_start',ee.Date.fromYMD(1, m, 1)); }).flatten() );
Step 6: Create and plot the chart
var title = { title: 'Monthly precipitation', hAxis: {title: 'Time'}, vAxis: {title: 'Precipitation (mm)'}, }; var chartMonthly = ui.Chart.image.seriesByRegion({ imageCollection: meanMonthlyP, regions: SriLanka, reducer: ee.Reducer.mean(), band: 'precipitation', scale: 2500, xProperty: 'system:time_start', seriesProperty: 'SITE' }).setOptions(title) .setChartType('ColumnChart'); print(chartMonthly);