(2011 - 2018)
As the alteration of the precipitation regime due to climate change, extreme precipitation events causing floods with the negative impacts on urban water infrastructure are observed today and expected to be observed in the future. This study examines the potential impacts of climate change and investigates the impact of these changes into urban stormwater network design. Rainfall analysis with stationary and nonstationary approach for observed and future conditions is performed for the (1950-2015 period) observed data of 5, 10, 15, 30 minutes and 1, 2, 3, 6 hour and projections (2015-2098 period) of 10, 15 minutes and 1, 6 hour for Ankara province, Turkey. Daily projections are disaggregated to finer scales, 5 minutes storm durations, then five minutes time series aggregated to the storm durations that are subject of interest and used for future period. Nonstationary Generalized Extreme Value (GEV) models and stationary GEV models for observed and future data are obtained. Nonstationary model results are in general exhibited smaller return level values with respect to stationary model results of each storm duration for the observed data driven model results. Considering the projected data driven model results; on average nonstationary models produce mostly lower return levels for mid and longer return periods for all storm durations and return periods except one hour storm duration. Depending on the models and Representative Concentration Pathways (RCP), there are different results for the future extreme rainfall input; yet all results indicate a decreasing extreme trend. The magnitude of future period extreme rainfall decreases with respect to observations. Return periods of the extreme rainfall increase in the future period therefore, not considering these trends may lead to overdesign of the stormwater network.
Existing urban infrastructure design criteria and assumptions may underestimate the loads such as peak flow, precipitation height, etc. under changing climate conditions. Extreme precipitation patterns that are used as design criteria for urban drainage networks is expected to change due to climate. Therefore, a strong need has emerged to study extreme events to reveal potential frequency and intensity alterations under changing climate conditions. In this study historical and future extreme precipitation and land use/cover change analyses results of Ankara province are applied for a newly built stormwater network of a pilot study area in Etimesgut, Ankara. Performance of the system investigated under current and changing conditions and different approaches such as stationary and nonstationary extreme value assumption. The system operated in a satisfactory state and it can be said that according to climate change projections for the extreme rainfall, the maximum volume that the system face will not exceed baseline design criteria throughout the projection period. Combination of changing climatic and land use/cover conditions also reveal a satisfactory performance for the baseline design which used 15 minutes storm duration and 2 years return period rainfall intensity and a runoff coefficient of 0,8 as design input. On the other hand the system may fail under the loads derived separately or together with longer storm duration (such as 30 minutes or more) or higher return periods (such as 5 years and more) that is computed from stationary and nonstationary observed data analysis which is a preferred design input for such a critical facility and area. Cost analyses of various options also conducted for the pilot study stormwater network according to the changing design inputs for the climate change and land use scenarios.