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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Keynotes Session 5A : Return levels of floods and droughts: how long will the past provide a valuable clue to the future?
Return levels of floods and droughts: how long will the past provide a valuable clue to the future?
Author : ARPITA MONDAL(1), P. P. MUJUMDAR(1, 2)
Hydrological extremes such as floods and droughts are expected to be altered through land and atmospheric processes
that are linked physically to a warming climate. Traditional assumptions of stationarity to estimate the risk associated
with such extreme events, have come under scrutiny in the light of global climate change. Using recent advancements in
the statistical extreme value theory which allow non-stationary modeling of changes in the frequency and severity of
extremes, we seek answers to the questions of how long will the historical hydrological design magnitudes or return
levels of floods and droughts hold good. The transient future return levels and their uncertainties are derived from
regional extreme streamflow projections that are modeled considering their associations with global warming. Nonstationary
formulations of two of the most important approaches in the Extreme Value Theory (EVT) are used, namely,
the block maxima approach for floods and the peak-over-threshold (POT) approach for droughts. Non-stationary scaling
of regional floods/droughts with global warming is first tested by a likelihood ratio test. For non-stationary possible future
realizations, we additionally seek answer to the question of how long will the stationary historical design magnitudes or
return levels of floods hold good, taking into account the uncertainties in observed and projected return levels. The
transient future ¡®effective¡¯ return levels are compared with those from observed naturalized streamflows and the time of
detection is computed as the time at which significant differences exist between them, accounting for the associated
errors. Two of the largest rivers in the Western United States, which are prone to hydrological extremes, are considered
in our analysis ¨C the Columbia River for floods and the Colorado River for droughts. No coherent change in return levels
of floods or droughts is detected across the projections. For some simulations though, detection is achieved within the
twenty-first century with earlier detection in design magnitudes of lower return periods.
File Size : 165,968 bytes
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Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Keynotes Session 5A
Date Published : 28/08/2015
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