Climate change is not only causing the air temperature to rise; the temperature of surface water is also rising. The water temperature affects the water quality and the ecological condition of a body of water. This map is the first starting point to see how vulnerable the water in your area is to warming.
How does heat change water quality?
For example, oxygen solubility in water will decrease, whereas oxygen consumption will often increase (Kosten, 2011). Blue-green algae thrive in temperatures exceeding 20 °C (Paerl and Otten, 2013). Furthermore, warm water is more conducive to pathogens, whilst climate change can affect the spread of diseases (Gallana et al., 2013). According to an assessment under the Water Framework Directive (CBS, 2016), the current quality of surface water is often mediocre, insufficient, or poor. In a country such as the Netherlands, in which many people work and engage in leisure activities in and around water, it is important for adaptation strategies to take account of the impact of climate change on water temperatures. This map serves as an initial point of departure for assessing the extent to which the water in your vicinity is prone to warming.
What does the map show?
The map provides an indication of the probability of high summer water temperatures in the current climate. It is based on the basic aquatic map , which distinguishes 23 different types of water for the top 10 bodies of water (PBL, 2010).
The data is linked to the depths. The calculation model is not suitable for water that is deeper than 3 m; consequently, the map only reflects water to a maximum depth of 3 m.
The data is linked to the depths. The calculation model is not suitable for water that is deeper than 3 m; consequently, the map only reflects water to a maximum depth of 3 m.
The Cool Water Tool (Jacobs, La Rivière, and Goosen, 2014) is a model that takes account of the weather impact on water temperature, but also of location-specific factors such as building density, building height, and flood depth.
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The model has been used to calculate water temperatures for summer periods (April – September) in the current climate and for c. 2050 according to the KNMI WH scenario. Out of the four KNMI’14 scenarios, the WH scenario features the largest number of warm days and nights.
For each year, the maximum length (in days) has been determined of periods featuring a consecutive water temperature in excess of 20 °C. The map reflects the average maximum period over the years. Use the magnifying glass to view the same map for the 2050 WH scenario.
The interaction between the atmosphere and the water was estimated at the scale of the neighbourhood. Four types of neighbourhoods or types of environment that are common in the Netherlands have been distinguished, according to the system described by Stewart and Oke (2012). To determine the depth of the water, assumptions were made. The actual depth was not measured. The calculations were carried out for three different depths.
How can this information be used?
The map can be used to gain an idea of the differences in warming between various water surfaces featuring various depths in the associated types of environment. The outcomes are too imprecise to warrant interpretation at the level of, e.g., a specific town pond. However, the map will be quite useful in assessing the need for further detailed research. Insight into surface water warming is relevant for, e.g., the designation of swimming water locations.
Although the water temperature is an important indicator of water quality, it is not the only factor. The number of nutrients in the water, the formation of different water layers and the flow rate are also of great influence on water quality (Paerl and Otten 2013).
