IAEA Isotope-enabled coupled catchment–lake water balance model, IWBMIso: description and validation

Abstract

The International Atomic Energy Agency (IAEA) Water Balance Model with Isotopes (IWBMIso) is a spatially distributed monthly water balance model that considers water fluxes and storages and their associated isotopic compositions. It is composed of a lake water balance model that is tightly coupled with a catchment water balance model. Measured isotope compositions of precipitation, rivers, lakes, and groundwater provide data that can be used to make an improved estimate of the magnitude of the fluxes among the model components. The model has been developed using the Object Modelling System (OMS). A variety of open source geographic information systems and web-based tools have been combined to provide user support for (1) basin delineation, characterization, and parameterization; (2) data pre-processing; (3) model calibration and application; and (4) visualization and analysis of model results. In regions where measured data are limited, the model can use freely available global data sets of climate, isotopic composition of precipitation, and soils and vegetation characteristics to create input data files and estimate spatially distributed model parameters. The OMS model engine and support functions, and the spatial and web-based tool set are integrated using the Colorado State University Environmental Risk Assessment and Management System (eRAMS) framework. The IWBMIso can be used to assess the spatial and temporal variability of annual and monthly water balance components for input to water planning and management.

Use of stable isotopes to understand run‐off generation processes in theRedRiverDelta

“…The IAEA Water Balance Model with Isotopes (IWBMIso) is a spatially distributed monthly water balance model that considers water fluxes and storage and their associated isotopic compositions (Belachew et al, ). Measured isotope compositions of precipitation, rivers, lakes, and groundwater provide data that can be used to make an improved flux magnitude estimate among the model components.…”

“…It should be stated that, in order to compute actual ETP, the model uses the MODIS‐derived vegetation cover percentage of the hydrological research units and assumes that all vegetated areas are predominantly characterized by transpiration, whereas the nonvegetated portion mainly by evaporation (Belachew et al, ). The actual ETP is proportional to the average of surface transpiration and evaporation, weighted by the fraction of vegetation cover (Maselli et al, ).…”

“…All necessary source data furnished to the IWBMIso model simulation for the three upstream subbasins of the Red River were extracted from the globally available datasets (Belachew et al, ).…”

A method for predicting hydrogen and oxygen isotope distributions across a region's river network using reach-scale environmental attributes

“…These factors are difficult to capture with empirical models of precipitation isotopes of the kind used in this study 405 (Bowen, 2010), however potential improvements to the precipitation isotope model could be made by incorporating highfrequency and event-based sampling, including back-trajectory calculations, and adjusting predictions based on spatial patterns of residuals (Bowen and Revenaugh, 2003;Baisden et al, 2016). Improved regional precipitation isotope models are likely to improve the performance of process-based isotope hydrology models, such as the Isotope-enabled coupled catchment-lake water balance model (Belachew et al, 2016), that are designed to quantify hydrological fluxes (e.g. between rivers, lakes and 410 groundwater) using water isotope data.…”

Current state and future challenges in stable isotope applications of the tropical hydrologic cycle (Invited Commentary)

“…Such models have proven key to advancing our understanding of the dynamics and forcing mechanisms that drive isotope variations across spatial and temporal scales, and opened up new possibilities for detailed analyses of processes affecting the isotopic composition of precipitation (Colose, LeGrande, & Vuille, ; Hoffmann, Werner, & Heimann, ; Jouzel, Hoffmann, Koster, & Masson, ; Risi, Bony, Vimeux, & Jouzel, ; Schmidt, LeGrande, & Hoffmann, ; Vuille, Bradley, Werner, Healy, & Keimig, ). Although less common, some modelling groups have also incorporated stable isotopic tracers into regional isotope‐enabled climate and hydrologic models (Belachew et al, ; Durán‐Quesada et al, ; Stadnyk, Delavau, Kouwen, & Edwards, ; Sturm, Hoffmann, & Langmann, ; Yoshimura, Kanamitsu, & Dettinger, ), allowing for more detailed atmospheric studies over regions of complex terrain or focusing on specific isotopic processes related to streamflow and run‐off generation or spatially distributed isotopic lake water balance. Because stable water isotopologues are tracers of the hydrologic cycle, they are on the other hand also ideally suited to test the realism of climate model parameterizations when simulating the tropical hydrologic cycle (Schmidt, Hoffmann, Shindell, & Hu, ) and can yield important modelling constraints for atmospheric water vapour transport, mixing, and phase change.…”