Too little or too dirty? Global modelling framework for analyses of sectoral water use responses under droughts and heatwaves

Abstract

Drought-heatwave events increase water use mainly for domestic and irrigation water use sectors (Cárdenas et al., 2023). Moreover, water quality deterioration caused by human activities is exacerbated by more frequent and longer-lasting extreme hydro-climatic events, such as droughts and heatwaves. These circumstances challenge the supply of water of suitable quality and increase the cross-sectoral competition forclean water. Water use models are useful in estimating responses in water demand and use ‑in terms of consumption and withdrawals‑ of the main water use sectors (i.e., irrigation, livestock, domestic, energy and manufacturing); however, there are few water use models that account for both water quantity and quality dimensions simultaneously. The main objective of our research is to assess the cross-sectoral water deficit due to sectoral competition for limited clean water resources, explicitly considering water quantity and water quality requirements. To address this objective a new sectoral water use model framework has been developed, that evaluates simultaneously water quantity and water quality requirements for the main water use sectors. This globally applicable model framework builds on the PCR-GLOBWB 2 hydrological model (Sutanudjaja et al, 2018) and DynQual v1.0 global surface water quality model (Jones et al, 2023), which simulates surface water temperature, salinity as indicated by total dissolved solids (TDS), organic pollution as indicated by biochemical oxygen demand (BOD), and pathogen pollution as indicated by faecal coliform (FC). Preliminary results show that high salinity (TDS) is the predominant water quality constituent limiting water use for irrigation most of the year; while for the domestic sector it is organic pollution, particularly in regions with limited water treatment capacities. For such sectors, accounting for water quality requirements lead to substantial reductions in surface water withdrawals over the Conterminous United States when compared to results obtained from only water quantity-based models. This modelling framework provides the basis for an integrated water scarcity assessment driven by changes in water quantity and quality under current and future droughts and heatwaves.