.. _app_hydroland:

HydroLand
=========

General description
-------------------

HydroLand is an open-source, component-based model coupling for land-surface
hydrology simulations (see the `Zenodo HydroLand repository <https://zenodo.org/records/17541709>`_).
It combines the mesoscale Hydrologic Model (`mHM <https://git.ufz.de/mhm/mhm>`_)
with the multiscale Routing Model (`mRM <https://git.ufz.de/destine_cats/mrm>`_)
through the standalone `hydroland <https://github.com/DestinE-Climate-DT/hydroland>`_
Python package in order to translate Climate DT forcing
into hydrological states, runoff, routed streamflow, and derived indicators.

The application is co-designed with users from the German Technical and
Scientific Association for Gas and Water (DVGW) and the European Environment
Agency (EEA). Its main use cases are freshwater availability, drought and flood
screening, and climate adaptation assessments for water management and
agriculture.

Within the operational workflow, HydroLand reads Climate DT forcing from the
GSV/OPA interface, optionally applies bias-adjusted precipitation and
temperature, and executes a five-step chain consisting of initialisation,
forcing preprocessing, `mHM`, `mRM`, and cleanup/restart management. The code
base supports `0.1` and `0.05` degree configurations with daily or hourly
execution. The current public guide focuses on the application workflow; an updated 
validation summary will be added in a forthcoming update.

Technical Description
---------------------

HydroLand is designed as an operational command-line application with explicit
steps for setup, preprocessing, simulation, routing, and cleanup. See the
:doc:`technical description <technical_des>` page for the workflow, restart
logic, forcing assumptions, and indicator chain.

Data portfolio
--------------

HydroLand produces gridded NetCDF products for land-surface hydrology and routed
river discharge, together with downstream indicator products. The current code
and cycle documents describe three main product groups:

- `mHM` flux/state files for evapotranspiration, soil water content, and runoff;
- `mRM` routed river discharge files (`Qrouted`);
- indicator products for aridity, soil moisture deficit, discharge percentiles,
  flood events, and drought events.

.. More detail on the current Data Lake delivery is summarised in the
.. :doc:`data portfolio <data_portfolio>` page. A first HydroLand test publication
.. is already available in the Data Lake. It was prepared to test how HydroLand
.. indicator products are packaged and exposed to users through the Climate DT data
.. infrastructure. The current package focuses on European IFS-NEMO indicator
.. products, while the operational HydroLand data collection is now being
.. produced.

Accessing the data
------------------

.. note::

   Data for this application will become available on the
   DestinE Data Lake in a forthcoming update.

Scientific Evaluation
---------------------

.. note::

   Scientific evaluation for this application will be available
   in a forthcoming update.

.. Validation and scientific assessment
.. ------------------------------------

.. An updated HydroLand validation summary is still being finalized. The planned
.. validation package will focus on the questions most relevant for users across
.. all HydroLand configurations: how well evapotranspiration climatology and
.. seasonality compare with reference datasets, how river discharge compares with
.. historical gauge records, how diagnostics such as the `alpha` and
.. `beta` KGE components behave across regions, and where the product is considered
.. more or less reliable for practical use. In this context, `alpha` refers to the
.. variability component and `beta` to the bias component of river-discharge
.. evaluation. These comparisons confront physically based climate-model
.. simulations with observational reference datasets, while recognizing that the
.. two are not expected to be directly comparable one to one.

.. The aim is not only to provide figures, but also to give clear guidance on
.. strengths, limitations, and fitness for use. This validation framework will be
.. applied consistently to the HydroLand IFS-NEMO, IFS-FESOM, and ICON
.. configurations.


.. .. toctree::
..   :maxdepth: 1

..   technical_des
..   data_portfolio