Droughts have an increasing impact on the entire European continent. As the frequency and intensity of droughts rise in many parts of Europe, the implementation of effective drought adaptation and mitigation strategies becomes increasingly important. However, it is not known how diverse tools are used in drought management with increasing drought severity. This study explores the role of Decision Support Tools (DSTs) in strategic and operational drought management in the Netherlands. Through a survey among national and regional water authorities, this study shows the increasing reliance of water managers on field measurements, Data Information Systems (DISs), stakeholder consultation, and legislation with increasing drought severity. Weather forecasts and expert knowledge remain important throughout all drought management phases. Despite the increased use of DISs with drought severity, the use of hydrological models does not follow the same trend. DISs, which often incorporate hydrological models, reveal a ‘hidden’ use of these models. Rather than serving as ‘key artifacts’ for modelers, they become active ‘participants’ in broader data systems during advanced phases of drought management. All these aspects influence key responsibilities in model use including appropriateness and transferability, reproducibility, and transparency. These factors are critical to consider when aiming to bridge the gap between science and policy in the application and development of DSTs.

Canals and canalized rivers form a major part of surface water systems in European delta cities and societal ambitions to use these waters increase. This is the first assessment of how suitability of these waters can improve for three important uses: transportation, thermal energy extraction (TEE) and recreation. We assess suitability with Suitability Indices (SIs) and identify which alterations in the water system are needed to improve SI scores in Amsterdam, The Netherlands, and Ghent, Belgium. The results show spatial variability in suitability scores. Current suitability for transportation is low (SI score = 1) to excellent (SI score = 4), for TEE fair (SI score = 2) to excellent (SI score = 4), and suitability for recreation is low (SI score = 1). Suitability could improve by enlarging specific waterway dimensions, increasing discharge and clarity, and by enhancing microbiological water quality. The same methodology can be applied to optimize designs for new water bodies and for more water uses.

Urban surface waters are used in many different ways. With increasing demand for human use functions, improved insight is required into the functional quality of these waters. A method to assess this functional quality in a systematic way and for a wide variety of use functions is not available. We propose to use suitability indices (SIs) for assessing the suitability of urban water bodies for a variety of specific human uses. This study provides a new protocol for this, building on the water quality index and ecosystem services approaches in literature, by extending traditional water quality parameters with other characteristics of water bodies that determine suitability for a specific use function. By assessing suitability instead of traditional water quality, the functional quality of a water body for all kinds of uses can be determined in a consistent way. The protocol was demonstrated to be effective in developing SIs for three specific urban water use functions, namely: thermal energy extraction, transportation of goods and primary contact recreation. Application of the suitability indices in a case study in the city of Amsterdam, The Netherlands, resulted in spatially explicit information about suitability of surface waters for the three selected use functions. Sub-scores per parameter showed which characteristics of the urban water bodies should be changed to improve the suitability for these three functions. In this way, the SI approach for assessment of the functional quality of urban surface waters can be used to support function-oriented planning, design and maintenance of urban surface water systems.

Scientific literature currently lacks comprehensive understanding of urban surface water use functions. This hampers sound analysis of the demand and potential supply of these functions. This study provides a comprehensive overview of potential use functions, by integrating knowledge from ecosystem services and integrated urban water management fields. Analysis of water-related management plans for Toronto and Amsterdam shows that surface water is currently being used for a variety of functions related to nutrition, energy, water regulation, recreation, symbolic use, transportation and floating buildings. Notably, many use functions involve in situ use, rather than water extractions. Interviewed water managers and spatial planners in both cities expect demand of most use functions to increase by 2040, especially demand for thermal energy extraction, recreation and transportation. Some identified novel demands, such as climate regulation and reuse of waste products from waterway maintenance. Increasing demand is mainly driven by urban growth, climate change and sustainability ambitions. This study found urban surface water uses that are usually not acknowledged in scientific literature on urban water management. This comprehensive overview supports planning, design, and maintenance of urban surface waters, laying the foundation for future research on supply and demand of urban water use functions.