var geometry = ee.FeatureCollection('users/www1573979951/HN_full');
var dataset = ee.ImageCollection("MODIS/MOD09GA_006_NDWI");
for(var i=2000;i<=2000;i++){
  var data_collection = dataset.filterDate(i+'-01-01',i+'-12-31').select('NDWI');
  print(data_collection)
  var YR_collection = data_collection.mean().clip(geometry);
  Export.image.toDrive({
    image: YR_collection,
    description: "HN_NDWI-"+i,
    fileNamePrefix: "HN_NDWI-"+i,
    scale: 500,
    region: geometry,
    maxPixels: 1e13,
    crs: "EPSG:4326",//投影方式
    folder: 'Modis'
  });
}