PCRFCD Brown Bag: Spatio-temporal characteristics of precipitation intensities in Arizona

Pima County Regional Flood Control District — Monthly Brown Bag Series

Spatio-temporal characteristics of precipitation intensities in Arizona: Implications for storm design

When: Wednesday, March 8, 12:00 – 1:00 PM
Where: 9th Floor Public Works Building, 201 N. Stone, Tucson AZ, 85701
Presenter: Eleonora Demaria, Southwest Watershed Research Center USDA-ARS

Extreme rainfall events are linked to flooding, property damage, and potential loss of life. As the atmosphere gets warmer, changes in its water-vapor holding capacity and shifts in circulation dynamics are expected to lead to changes in the characteristics of precipitation. Positive trends in daily precipitation extremes have been reported globally and within the U.S., with indications that sub-daily precipitation extremes are increasing, creating strong implications for infrastructure design.

Observed sub-daily precipitation intensities from the USDA-ARS Walnut Gulch Experimental Watershed located in southeastern Arizona are used to evaluate temporal trends and to develop intensity-duration-frequency (IDF) curves under stationary and non-stationary climatic conditions. Using a Bayesian method that takes into account linear trends in the time series, we estimate the risk of structural failure associated with design storms. Our results show that the stationary climate assumptions lead to much lower estimated sub-daily intensities than those under non-stationary assumptions, with larger absolute differences found for shorter durations and smaller return periods.

The risk of failure (R) of a hydraulic structure will increase under the consideration for non-stationary effects with absolute differences of 25% for a 100-year return period (T) and a project life of 100 years. This indicates that the effect of non-stationarity, due to natural variability or to climate change, needs to be considered in future projects designs that require a greater level of protection.

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