NIWA's Island Climate Update "Water Watch"

Source code, scripts and notebooks for the NIWA Island Climate Update (ICU) "Water Watch": Drought monitoring and forecasting for the Southwest Pacific

Requirements

The first step is to create a suitable mamba (alternative to conda) environment, this can done using the ICU_ops environment file

To create this environment using mamba:

$ mamba env update -n ICU_ops -f ICU_ops.yaml 

The package lmoments3 is (at the time of this writing) not conda / mamba installable, so you need to use pip

$ pip install lmoments3

Note that this is entirely optional, it is only used if you choose to derive parametrized (Gamma distribution) climatological quantiles instead of empirical quantiles from the precipitation amounts. Operationally we are currently using the empirically-derived quantiles, as it e.g. ends up matching perfectly the tercile probabilistic forecasts provided by ECMWF for the C3S MME.

Installation

You should be able to install this pure Python package in the ICU environment using

$ python setup.py install

after having cloned the repository and natigated to the "ICU_Water_Watch" directory that contains the setup.py file

Background

The aim of these modules, scripts and notebooks is to combine realtime rainfall monitoring in the Southwest Pacific, using the NASA GPM-IMERG satellite product, and probabilistic monthly and seasonal forecast (data from 9 different General Circulation Models, or GCMs) to highlight regions that are and / or will be in potential "water-stress" conditions: i.e. - in a nutshell - where significant rainfall deficits have been recorded over the past few months, and the monthly or seasonal forecasts indicate high probability for dry conditions to persist or worsen.

Data

1) The GPM-IMERG satellite rainfall estimates

The past 30, 60, 90, 180 and 360 days rainfall accumulations, anomalies, percentile of scores and Standardized Precipitation Index (SPI) are derived from the daily, GPM-IMERG mission. The near realtime (2 days lag) data is downloaded from https://gpm1.gesdisc.eosdis.nasa.gov/data/GPM_L3/GPM_3IMERGDL.06

The climatologies have been pre-computed from all the available data over the 2001 - 2020 period.

3) Monthly and seasonal rainfall forecasts from the C3S Multi-Model Ensemble (MME)

Probabilistic forecasts are derived from a Multi-Model Ensemble (MME) including forecasts from the following 9 Coupled Ocean-Atmosphere GCMs:

• ECMWF (SEAS5)
• UKMO (GloSea6)
• Meteo-France (Météo-France System 8)
• DWD (GCFS2.1)
• CMCC (SPSv3.5)
• NCEP (CFSv2)
• JMA (CPS2)
• ECCC system 1 (GEM-NEMO)
• ECCC system 2 (CanCM4i)

The details for the different GCMs can be found here

A summary of the available data (hindcasts and forecasts for the different systems) is available here

The forecast data (post 2017) for this MME contains in excess of 370 members.

The data is available from the Copernicus Climate Data Store

Organisation of this repository

• ICU_Water_Watch: contains the source code itself, i.e. the collection of functions used for the data retrieval, processing, calculation and mapping of the various rainfall monitoring and forecasting products part of the ICU "Water Watch", the code is organized in 6 main modules:

  • utils.py: General utility functions
  • geo.py: Manipulation of geometries (from shapefiles), creation of masks, etc
  • GPM.py: Functions related to the download, processing and the calculation of diagnostics from the near-realtime GPM-IMERG data
  • C3S.py: Functions related to the download, processing and derivation of probabilistic forecasts from the C3S Multi-Model Ensemble
  • verification.py: Functions related to the validation of the C3S individual GCMs and MME
  • plot.py: Plotting and mapping functions

• notebooks: contains all the notebooks, organized in 3 folders: GPM, C3S and verification, these notebooks illustrate the various processing steps, and also include the code used to calculate the various climatological quantities from the GPM-IMERG and C3S datasets.

• scripts: contains the python scripts, designed to be run from the command line, with keywords arguments, as part of the operational suite

Credits

The development of this software was made possible by funding from NIWA's "core" (SSIF) funding under projects PRAS2101 and CAVA2101, as well as co-funding from MBIE project C01X1813 ("Smart Ideas" project on seasonal climate forecasting).

Acknowledgments

Thanks go as well for support, feedbacks and advice to Doug Ramsay, Dr. Andrew Lorrey and Ben Noll from NIWA, as well as John Marra, James Potemra and Richard Heim at NOAA.

References

• Fauchereau N., Ramsay D., Lorrey A.M., Noll B.E (in preparation): Open data and open source software for the development of a multi-model ensemble monthly and seasonal forecast system for the Pacific region. To be submitted to Climate Services, and preprint on ESSOAR

• Fauchereau N., Lorrey A.M, Noll B.E. (in preparation): On the predictability of New Zealand’s seasonal climate from General Circulation Models forecasts and observational indices. To be submitted to Weather and Climate.

Additional material and references

Coming soon !