DynQual v1.0: a high-resolution global surface water quality model

Maintaining good surface water quality is crucial to protect ecosystem health and for safeguarding human water use activities. However, our quantitative understanding of surface water quality is mostly predicated upon observations at monitoring stations that are highly limited in space and fragmented across time. Physical models based upon pollutant emissions and subsequent routing through the hydrological network provide opportunities to overcome these shortcomings. To this end, we have developed the dynamical surface water quality model (DynQual) for simulating water temperature (Tw) and concentrations of total dissolved solids (TDS), biological oxygen demand (BOD) and fecal coliform (FC) with a daily time step and at 5ĝarcmin (ĝ1/4ĝ10ĝkm) spatial resolution. Here, we describe the main components of this new global surface water quality model and evaluate model performance against in situ water quality observations. Furthermore, we describe both the spatial patterns and temporal trends in TDS, BOD and FC concentrations for the period 1980-2019, and we also attribute the dominant contributing sectors to surface water pollution. Modelled output indicates that multi-pollutant hotspots are especially prevalent across northern India and eastern China but that surface water quality issues exist across all world regions. Trends towards water quality deterioration have been most profound in the developing world, particularly sub-Saharan Africa and South Asia. The model code is available open source (10.5281/zenodo.7932317, Jones et al., 2023), and we provide global datasets of simulated hydrology, Tw, TDS, BOD and FC at 5ĝarcmin resolution with a monthly time step (10.5281/zenodo.7139222, Jones et al., 2022b). These data have the potential to inform assessments in a broad range of fields, including ecological, human health and water scarcity studies.