Femke Schasfoort (Netherlands) 1; Marnix Van Der Vat (Netherlands) 1; Marjolein Mens (Netherlands) 1; Paul Van Den Hoek (Netherlands) 2; Karel Van Hussen (Netherlands) 3; Susanne Groot (Netherlands) 4; Nico Polman (Netherlands) 5
1 - Deltares; 2 - Ministry of Infrastructure and the Environment; 3 - Ecorys; 4 - HKV Consultants; 5 - Wageningen Economic research
As temperatures are rising, summers in the Netherlands are expected to become hotter and drier, which could lead to a lack of freshwater for farming, industry, drinking water, navigation and nature. Under the first phase of the Delta Programme for the Netherlands (2012–2016), mitigating measures were supported by analyzing benefits for only a few characteristic drought years. This traditional method turned out to be incomplete and uncertain, because effectiveness of measures highly depends on the progression of a drought over the year, its spatial distribution and its probability of occurrence. More insight into the impact of measures for a wide range of drought events is expected to lead to better-informed decisions on measures. A drought risk approach was therefore developed, in which risk is defined as the annual expected value of the (negative) economic impact of water shortages. The applicability of this approach was tested in two Dutch case studies. In this presentation we will show the results from the two applications and discuss the lessons learnt for further developing drought risk analysis methods.
The drought risk analysis method provides a step-wise and rational approach to assess potential impacts of measures on the system for different stakeholders, under various meteorological and hydrological conditions. Five water users were identified that potentially are most affected by a lack of fresh water: agriculture, navigation, drinking water, industry and nature. Dose-effect relationships (‘impact modules’) were developed for each water user and connected with mainstream hydrological models. This resulted in a 100 year economic impact time series, from which a risk curve was derived (showing the probability distribution of the total drought impact).
The method has been applied in a regional case where surface water supply is important and in a local case where groundwater is important. The results show that risk curves are helpful in understanding the current and future risks for the different water users. Furthermore in de local case study, detailed water system models were considered to be essential to obtain a sound analysis of water shortages, its impacts as well as the effect of measures.
The results indicate that using a risk-based approach can improve the assessment of drought risk and therefore also the estimation of costs and benefits of drought measures. The approach is expected to be applicable in other countries as well.