A New Framework for Incorporating Nonstationarity in Intensity-Duration-Frequency Curves Under a Changing Climate

Abstract:

IDF curves are the basis for water infrastructure systems planning, development and management. The assumptions made in IDFs generation have to be revisited under the changing climate. The current practice of IDFs development includes the use of past climate information and assumption of stationary behavior. They both may result in underestimation of the extreme rainfall intensity, and consequently the infrastructure system’s capacity to deliver a required level of service. To address the impacts of climate change on the development of IDFs, the IDF_CC web-based tool has been developed and implemented in Canada (www.idf-cc-uwo.ca) by the University of Western Ontario and the Institute for Catastrophic Loss Reduction. This presentation is focused on the further improvement of the IDF_CC methodology by introduction of nonstationarity into IDFs development process. The new methodology includes: (i) fitting a theoretical probability distribution to annual maximum precipitation data series, by considering different trends in the distribution parameters; (ii) downscaling the climate information in time and space to incorporate future climate projections and generate future sub-daily precipitation time series; (iii) assess the need for considering nonstationarity in IDFs development; and (iv) updating IDF curves for changing conditions. In this methodology, the time is used as a covariate to introduce a nonstationary behavior. The main strength of the proposed procedure is the assessment of the statistical significance of nonstationarity before developing nonstationary IDFs. The methodology has been demonstrated using data from six selected precipitation stations across Canada. The future IDF curves developed using the proposed methodology show (i) the increase in magnitude and frequency of rainfall intensities, when compared to the curves developed using the observed data; and (ii) intensification of these impacts with the introduction of nonstationary behavior. These findings warranty the need for updating the IDF curves as one of significant climate change adaptation measures.