Google Earth Engine Tutorial: Map Annual Frost Days with ERA5

Google Earth Engine (GEE) is a powerful platform for geospatial analysis and remote sensing. To map annual frost days using the ERA5 dataset, follow this structured approach:

• Step 1: Initialize and Load ERA5 Dataset
  
  Use the following code to load the ERA5 temperature data. ERA5 provides high-resolution near-surface temperature data (t2m) at 0.25° spatial resolution.
  
var era5 = ee.ImageCollection("ECMWF/ERA5")
.select('t2m')
.filterDate('2010-01-01', '2020-12-31');

• Step 2: Define Frost Day Threshold
  
  Frost days are typically defined as days when the near-surface temperature (t2m) falls below 0°C.
  
var frostThreshold = 273.15; // 0°C in Kelvin

• Step 3: Process Monthly Data
  
  Iterate through each month to calculate frost days. For each month, compute the number of days where temperature is below the threshold.
  
var frostMonths = era5.map(function(image) {
var month = image.date().get('month');
var year = image.date().get('year');
var frostMask = image.select('t2m').lt(frostThreshold);
return frostMask.multiply(1).set('month', month, 'year', year);
});

• Step 4: Aggregate Annual Frost Days
  
  Combine monthly frost days into annual totals using .reduce(ee.Reducer.sum()).
  
var annualFrost = frostMonths.reduce(ee.Reducer.sum());

• Step 5: Visualize the Map
  
  Add the annual frost days image to the map and define visualization parameters.
  
Map.addLayer(annualFrost, {min: 0, max: 365, palette: ['white', 'blue']}, 'Annual Frost Days');

• Step 6: Export the Result
  
  Export the map as a GeoTIFF or other format using the Export API.
  
Export.image.toDrive({
image: annualFrost,
description: 'annual_frost_days',
folder: 'GEE_Exports',
fileNamePrefix: 'era5_frost',
scale: 25000,
region: geometry,
maxPixels: 1e10
});