if landuse == 'Landuse1':
    if hyd == 'Fair':
        lut_file = r'C:/temp/lu1fair.txt'
    elif hyd == 'Good':
        lut_file = r'C:/temp/lu1good.txt'
    elif hyd == 'Poor':
        lut_file = r'C:/temp/lu1poor.txt'

if landuse == 'Landuse2':
    if hyd == 'Fair':
        lut_file = r'C:/temp/lu2fair.txt'
    elif hyd == 'Good':
        lut_file = r'C:/temp/lu2good.txt'
    elif hyd == 'Poor':
        lut_file = r'C:/temp/lu2poor.txt'

UnboundLocalError: local variable 'lut_file' referenced before assignment