IAHR has organized an Online Forum, which is a week-long even intended to bring together the continually evolving knowledge and innovations of the hydro-environment community. I attended the session Hydraulic Design Guidance in a Changing Climate. This sought to discuss the scientific background and the point of view of funding agencies about the design criteria in water projects under climate variability scenarios in a set of presentations by Filippo Giorgi, William Young, Roberto Ranzi, Bregje van Wesenbeeck and Van Thanh Van Nguyen. i’d like to share my impressions with you and perhaps inspire you to attend some of the final parts of the very interesting program of the Online Forum.
Filippo Giorgi, a climatologist, talked about the effects of global warming go the characteristics of precipitation. Whereas evaporation is a slow and widespread process, precipitation is highly localized and intermittent (5-10% of the time). Because it doesn’t rain all the time, the mean is less interesting than the higher moments of the probability distribution. The temperature over land and of the sea surface is expected to increase, and as a result also evaporation. Because there is a balance, precipitation also must increase. All models predict this. This is usually 1-2 % per degree of global warming. This is not evenly distributed over the globe, with an increase at high latitudes, a decrease in subtropical regions, and an increase in equatorial belt. The basic “rich get richer, poor get poorer” pattern persists over the subsequent generations of climate models. More interesting than the mean precipitation is its intensity. Models predict a higher likelihood for high (and unprecedented) intensity precipitation. But even though we get more precipitation, the number of dry events is also expected to increase. The likelihood of low precipitation events is predicted to decrease, however. Wet spell length and area of precipitation are expected to decrease, dry spell length is expected to increase. Precipitation intensity is expected to increase by 4-5% per degree Celsius of global warming. To summarize, both more high intensity events, which are shorter, more intense, less frequent and less widespread, and more droughts are expected. This will pose significant additional stress to the sustainable development of countries.
William Young (lead water resources specialist at the World Bank) gave a high level view on how the World Bank approaches climate change. A new climate change action plan has just been published, which builds on the pillars people, nature and partners, with a matching grid framework and list of actions: aligning climate and development, prioritizing key systems transitions, and financing to support the transitions. All new operations will be Paris-aligned by 2023. A range of mechanisms is applied in operations, notably also using a shadow price of carbon to account for carbon externalities. The World Bank has also established a climate change knowledge portal (climateknowledgeportal.worldbank.org). A number of publications (guidance notes, design briefs) are available, including a decision tree framework for deciding under the uncertainties of climate change. This has been applied to many projects. Many reports are available on openknowledge.worldbank.org.
Roberto Ranzi illustrated that some effects of climate change are very clear, e.g. the melting of Greenland ice, but some show a lot of regional variability, for example flood risks. More and more standards require climate change to be taken into account in engineering practice. A monograph is in preparation which aims to offer guidance in assessing the impact of climate change and to discuss the adaptation practices for engineering, offering guidance for designing storm water drainage systems. A combination of “grey” and “green” solutions is deemed necessary.
A focus on nature based solutions in reducing disaster risks and adapt to climate change was presented by Bregje van Wesenbeeck (Deltares/TU Delft). It resembles “classical” engineering by treating nature as one of the subsystems to consider. For example, for a mangrove ecosystem, it makes more sense to put the coastal defense beyond the mangroves, so not at the low tide level, allowing the mangrove system to survive and continue its role in coastal protection. Nature based solutions can help to both mitigate (by sequestration of carbon) and adapt (by trapping sediment) to climate change. Nature based solutions can self-repair (grow back) to some degree, when damaged. General rules for a successful application of nature based solutions include an assessment of the natural system, cross-sectoral collaboration, principles of ecological restoration (looking at the ecosystem that was there in the past), and involvement of communities and stakeholders.
In the final presentation of this session, Van Thanh Van Nguyen (McGill University) talked about considering climate change in the design of urban water infrastructure from the Canadian experience. Extreme rainfall events are on the rise in Canada as well. For designing infrastructure, relevant aspects are measurement, forecasting and projections, with attention to the relevant spatial and temporal scales. A technical guide has been developed for this. Four different atmospheric processes have been identified that may be responsible for extreme rainfall events, occurring over different parts of the country. The scale of a storm determines its interaction with a river basin. The time and spatial scale of measurements and models determine the outcome of analyses and models to a significant degree. As a result, coarse climate change simulations from global circulation models are inadequate for impact studies at regional and local points scales. Researchers are working on including convection in climate models, which is an important process in generating extreme rainfall events. Also, different types of downscaling methods may be helpful to address this issue, resulting in useable and representative runoff estimates.
The first presentation provided a very good reminder of the mechanisms that affect the availability of water in the framework of climate change. Although the focus of the last 4 of the five presentations was focused on a different type of water infrastructure than I am (and most of us at KWR are) working it, it was nevertheless an inspirational overview, from technical details w.r.t. to climate model downscaling to insights for implementation.
Many more interesting speakers are lined up for the rest of the week-long event. Have a look at https://www.iahr.org/index/detail/406