sebvi commented 3 years ago

Branch

https://github.com/wmo-im/GRIB2/tree/issue-54

Summary and purpose

This document propose to add a new entry for "potential evapotranspiration rate" in Code table 4.2 discipline 2, category 0.

Action proposed

The team is requested to approve the content of this proposal for inclusion with the next update of the WMO Manual on Codes.

Discussions

The Copernicus Climate Change Service (C3S) project ULYSSE (mULti-model hYdrological SeaSonal prEdictionS system) provides a “seamless” multi-model hydrological seasonal prediction system using four state- of-the-art hydrological models (HMs) at a spatial resolution of 0.1 deg globally. Four HMs (JULES, HTESSEL, mHM, PCR-GLOBWB) will deliver forecasts of surface temperature, total precipitation, evapotranspiration, potential evapotranspiration, snow water equivalent, snowmelt, total volumetric soil moisture, total runoff and discharge. All these parameters, except potential evapotranspiration are well defined in GRIB2. We would like to propose to include in Code table 4.2 discipline 2, category 0

PET ("potential evapotranspiration rate" also called "reference crop evapotranspiration" ET~o~) is defined as "the amount of water that would be evaporated and transpired by a short green crop (grass) of uniform height, completely shading the ground, if there were sufficient water available". If the "actual evapotranspiration rate" (ET) is considered "the net result of atmospheric demand for moisture from a surface and the ability of the surface to supply moisture, then PET is a measure of the demand side." There are numerous methods to estimate PET, e.g., the Thornthwaite equation (1948), Penman-Monteith equation (1965), Priestley–Taylor (1972), Hargreaves and Samani (1982). Since the PET is required for the estimation of irrigation rates worldwide, the FAO provided a standardisation procedure called the FAO Penman-Monteith equation (http://www.fao.org/3/x0490e/x0490e06.htm#equation ), which is commonly used in hydrological modelling and irrigation scheduling.

Detailed proposal

add an entry in Code table 4.2, discipline 2, category 0 Octet Meaning Units 40 Potential evapotranspiration rate kg m-2 s-1

amilan17 commented 3 years ago