def add_wgi(image):
    """
    Calculates the Water Adjusted Green Index (WGI)
    """
    wgi = image.expression(
        'NDWI * GI', {
            'NDWI': image.select('NDWI'),
            'GI': image.select('GCVI'),
        }
    ).rename('WGI')

    return image.addBands(wgi)