Map water from space

Flooding in 2017

step 1: import the images

// import data
var before = ee.Image("COPERNICUS/S2/20170207T050601_20170207T050557_T44NMM");
var after = ee.Image("COPERNICUS/S2/20170528T050611_20170528T050606_T44NMM");

step 2: display the images in swir1, nir and red

// display swir1, nir , red
Map.addLayer(before,{min:0,max:6000,bands:"??"},"before");
Map.addLayer(after,{min:0,max:6000,bands:"??"},"after"

step 3: calculate the ndwi

// calculate the ndwi
var waterBefore = before.normalizedDifference(["B3","B8"]);
var waterAfter  = after.normalizedDifference(["??","??"]);

step 4: show the water map

Map.addLayer(waterBefore,{min:-0.5,max:0.5},"water before");
Map.addLayer(waterAfter, {min: -0.5,max:0.5},"water after");

step 5: get the water and mask the land

// calculate the inundated area
var watermask = waterAfter.gt(??);
Map.addLayer(watermask.mask(watermask),{palette:"??"},"flooded");