import math


def water_saturation_vapour_pressure_wmo(t):
    """Returns the water vapour pressure according to World Meteorological Organization, Technical Regulations,
    Basic Documents No. 2, Volume I - General meteorological standards and recommended practices, Appendix A,
    WMO-No. 49, Geneva 2011, updated 2012.
    :param t: water temperature (°C)
    :return: water vapour pressure in Pascal (Pa)
    """
    t += 273.15
    return 100.0 * 10.0**(10.79574 * (1-273.16/t) - 5.02800 * math.log10(t/273.16) +
                          1.50475E-4 * (1 - 10**(-8.2969 * (t/273.16-1))) +
                          0.42873E-3 * (10**( 4.76955 * (1 - 273.16/t)) - 1) + 0.78614)