Python code for 'Limited comparability of global and local estimates of environmental flow requirements to sustain river ecosystems'
This repository contains python code associated with Messager, M. L., Dickens, C. W. S., Eriyagama, N., & Tharme, R. E. (2024). Limited comparability of global and local estimates of environmental flow requirements to sustain river ecosystems. Environmental Research Letters, 19(2), 024012. https://doi.org/10.1088/1748-9326/ad1cb5
Environmental flows (e-flows) are a central element of sustainable water resource management to mitigate the detrimental impacts of hydrological alteration on freshwater ecosystems and their benefits to people. Many nations strive to protect e-flows through policy, and thousands of local-scale e-flows assessments have been conducted globally, leveraging data and knowledge to quantify how much water must be provided to river ecosystems, and when, to keep them healthy. However, e-flows assessments and implementation are geographically uneven and cover a small fraction of rivers worldwide. This hinders globally consistent target-setting, monitoring and evaluation for international agreements to curb water scarcity and biodiversity loss. Therefore, dozens of models have been developed over the past two decades to estimate the e-flows requirements of rivers seamlessly across basins and administrative boundaries at a global scale. There has been little effort, however, to benchmark these models against locally derived e-flows estimates, which may limit confidence in the relevance of global estimates. The aim of this study was to assess whether current global methods reflect e-flows estimates used on the ground, by comparing global and local estimates for 1194 sites across 25 countries. We found that while global approaches broadly approximate the bulk volume of water that should be precautionarily provided to sustain aquatic ecosystems at the scale of large basins or countries, they explain a remarkably negligible 0%–1% of the global variability in locally derived estimates of the percentage of river flow that must be protected at a given site. Even when comparing assessments for individual countries, thus controlling for differences in local assessment methods among jurisdictions, global e-flows estimates only marginally compared (R 2 ⩽ 0.31) to local estimates. Such a disconnect between global and local assessments of e-flows requirements limits the credibility of global estimates and associated targets for water use. To accelerate the global implementation of e-flows requires further concerted effort to compile and draw from the thousands of existing local e-flows assessments worldwide for developing a new generation of global models and bridging the gap from local to global scales.
This repository includes the portions of the analysis conducted in Python, which encompass all spatial formatting of the data prior to data analysis. This analysis workflow needs to be conducted prior to conducting data analysis in R with code in the following repository: https://github.com/messamat/globalEF_testR.
These scripts are annotated but could be challenging to follow. If you encounter any trouble, please don't hesitate to contact Mathis L. Messager for comments and clarifications by email or to log an issue in github.
Files needed to run this analysis are available by downloading the study's figshare permanent repository. The /data folder in the figshare repository contains raw data and the directory structure enables users to reproduce our study using the scripts herein.
All GIS analyses in this study require an ESRI ArcGIS Pro license including the Spatial Analyst extension, which itself requires a Windows OS. We used the Python Arcpy module associated with ArcGIS Pro 3.0 in Python 3.9.
- global_EF_comparison_setup.py : import libraries, define folder structure, basic utility functions
- EF_utils.py: functions to pre-process and compute e-flows from netCDF files (ith the xarray module)
- 00_download_HydroRIVERS_HydroATLAS.py: download HydroRIVERS and RiverATLAS database. Export RiverATLAS attribute table to csv.
- 01_download_isimp2b.py: download discharge and total runoff data from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) simulation round 2b for 16 combinations of Global Circulation Models (GCMs) and GLobal Hydrological Models (GHMs)
- 02_preprocess_isimp2b.py: aggregate GHM outputs from ISIMIP 2b from daily to monthly time series, then compute e-flow estimates from ISIMIP 2b hydrological data with all global methods (Tennant, Tessman, Variable Monthly Flow, Q90_Q50, Smakhtin's flow duration curve shift)
- 03_preprocess PCR-GLOBWB.py: compute e-flows for higher-resolution version of one of the global hydrological models used in the main analysis — PCR-GLOBWB 2.0 at a spatial resolution of 5 arc-min, equating to 9 km at the equator, as implemented in Li et al (2019). Obtained data from personal communication with Dr. ir. Edwin H. Sutanudjaja.
- 04_downscale_EFs.py: downscale all global mean annual flow (MAF) and e-flow estimates based on runoff to yield estimates in terms of discharge at 0.25 arc-min (approximately 500 m at the equator). Estimates in terms of runoff (in m3 s-1 m-2) were first resampled to 0.25 arc-min pixels and then routed along the river network to simulate the flow of water across the landscape and produce estimates in terms of discharge (in m3 s-1). This river network routing was performed by simple area-weighted flow accumulation using the HydroSHEDS drainage direction grids at a resolution of 0.25 arc-min network (Lehner et al 2008, Lehner and Grill 2013).
Note that substantial manual quality-checking and editing was performed on the location of the e-flow assessment sites, a process that cannot be programatically reproduced.
- 05_download_localEFdata_france_rhone.py: download e-flow assessment reports for the Rhone River Basin in France
- 06_download_localEFdata_Mexico.py: download supplementary information from Salinas-Rodriguez et al. 2021 for Mexico and river basin polygons from the Open Data portal of the Comisión Nacional del Agua.
- 07_preprocess_localEFdata_france_rhone.py: pre-format extracted data from e-flow assessment reports for the Rhone River Basin, merge these data to ecological condition data from the European Water Framework Directive.
- 08_format_points.py: quality-check data for all e-flow sites and co-register them to the HydroRIVERS digital river network.
- 09_link_sites_globalEF.py: extract global estimates of MAF and e-flows for all sites
- 10_link_sites_RiverATLAS.py: extract hydro-environmental variables from the RiverATLAS database for all sites
- 11_post_process_isimip2b_: extract global estimates of e-flows for all river reaches in the HydroRIVERs database for mapping