edcrop 0.0.0

A sript to simulate field-scale evapotranspiration and drainage

ed_py

Evapotranspiration is one of the major components of Earth’s water balance, being the sum of evaporation and plant transpiration from the land and ocean surface.

Ed.py is a Python script that, using climate input, can be used to simulate field-scale evapotranspiration and drainage from the root zone of an area covered with a crop, a wetland, or a forest.

The conceptual model implemented in ed.py is a modification of the Evacrop model by Olesen and Heidmann (2002), which itself builds on the Watcros model by Aslyng and Hansen (1982). The ed.py conceptualization is based on considerations regarding the physical processes that are important for turning precipitation and irrigation into either evaporation, transpiration, or drainage from the root zone: Temperature determines whether precipitation falls as rain or snow, and it determines when snow thaws and infiltrates. The vegetation intercepts a part of precipitation, while the rest infiltrates into the ground. The infiltrated water will either evaporate, be absorbed by plant roots, be stored in the soil, or drain from the root zone. Potential evaporation is distributed between vegetation and soil, where the former part drives evaporation of intercepted water and plant transpiration from the green leaf area, while the latter part drives evaporation from the soil. The soil’s ability to store water depends on its field capacity; when the water content exceeds field capacity, water will gradually drain downwards. Furthermore, it is assumed that the annual life cycle of crops and wetland vegetation can be described by growing degree-days alone, while for forests the life cycle is described by a calendar. For irrigation, either (i) date and amount are input, or (ii) they are determined automatically by ed.py using certain criteria.

There are two alternative soil water balance functions to choose between in ed.py. The first alternative is an almost straight copy of the function used in the original Evacrop code by Olesen and Heidmann (2002), simulating flow through the soil profile as flow through two linear reservoirs using daily time steps. However, it can simulate macro-pore drainage, which the original Evacrop cannot. The second alternative simulates flow through the soil profile as flow through four linear or nonlinear reservoirs using daily or sub-daily time steps. For nonlinear reservoirs, ed.py uses Mualem – van Genuchten like functions. It also simulates gravity driven macro-pore flow as well as surface runoff.

As input, given in text files, ed.py requires daily temperature, precipitation, and reference evapotranspiration. It also requires information about combination(s) of soil type and vegetation type to simulate. One can choose between seven default soil types and fifteen default vegetation types, or one can manually input information for other types of soil or vegetation. In a single model run, ed.py can loop through lists of climate files, soils, and vegetation.