WBM: A scalable gridded global hydrologic model with water tracking functionality

Abstract

Abstract. This paper describes the University of New Hampshire Water Balance Model, WBM, a process-based gridded global hydrologic model that simulates the land surface components of the global water cycle and includes water extraction for use in agriculture and domestic sectors. WBM has a long publication history; here we describe the first fully open source WBM version. This version includes a suite of water source tracking modules that enable analysis of flow-path histories on water supply. Earlier descriptions of WBM methods provide the foundation of the most recent model version detailed here. WBM is available here: https://github.com/wsag/WBM. WBM is written in the perl data programming language (PDL), making use of several open-source perl libraries. As a convenience we also provide a Singularity container that simplifies installation of dependencies. We present an overview of the model functionality, utility, and validation of global river discharge and irrigation water use using data from the Global Runoff Data Centre and FAO statistics. A key feature of WBM is the ability to identify the partitioning of sources for each stock or flux within the model. Therefore, users can determine what proportion of any flux consists of each of the primary inputs of water to the surface of the terrestrial hydrologic cycle, previously extracted water for human uses, or runoff generated from any place on the Earth’s surface. Such component tracking provides both a more fully transparent model in that users can identify the underlying mechanisms generating the simulated behavior, as well as perform model experiments in new ways.

Distinguishing Direct Human‐Driven Effects on the Global Terrestrial Water Cycle

“…These outcomes consist of historical time series of different hydrological variables (evapotranspiration, runoff, soil moisture, storage change). Further model details and documentation can be found in the original sources (Grogan, 2016; Grogan et al., 2022; Wisser et al., 2010).…”

“…The global gridded WBM (Grogan, 2016; Grogan et al., 2022; Vörösmarty et al., 1989; Wisser et al., 2010) simulates water flow at daily time steps, both as vertical water exchange between the land surface and atmosphere (quantifying evapotranspiration) and as horizontal water transport (quantifying runoff and its area integration into stream/river discharge), with spatial resolution of 0.5°. The model simulates the direction of hydrological flows and the effect that different human activities (e.g., dams) and climate change (e.g., precipitation changes) have on hydrological outcomes.…”

“…To address these research needs and contribute to bridging current gaps, this study aimed to identify human effects on multiple key water balance variables of the hydrological system (evapotranspiration, runoff, soil moisture, storage change), and emergent effect patterns in and across different parts of the world. To achieve this aim, we used the Water Balance Model (WBM), a global gridded hydrological model (Grogan et al., 2022). This enabled exploration of spatial variability and regional patterns in the interactions of human activities with hydrology on multiple spatial scales, from pixel up to global, including in previously uninvestigated parts of the world.…”