Assessing the changes of return periods of floods and droughts in response to climate change using a hydrologic modeling approach

Abstract:

When accessing the impacts of climate change on water resources, it is important to estimate changes in the frequencies and magnitudes of projected floods and droughts in response to climate change, considering that most disasters result from these hydrological extremes. The objective of this study is to estimate the changes of return periods of floods and droughts based on projected future streamflows in the Illinois River Watershed according to various climate change models. Future streamflows are simulated by combining data from 59 climate model scenarios with the Soil and Water Assessment Tool (SWAT) hydrologic model. Subsequently, a Gumbel distribution (Extreme Value Type І) is fitted to the annual maximum simulated streamflow to derive the number of return periods of future hydrological extremes. The annual minimum 7-day average streamflow has been adopted for drought analysis. A Weibull distribution (Extreme Value Type Ш) is used to analyze the return periods of low flows. The 10-year and 100-year return periods of floods and droughts from 2020 to 2049 and from 2070 to 2099 are analyzed in comparison to streamflows from 1975 to 2004. Results indicate that average streamflow predicted from 33 (2020-2049) and 29 (2070-2099) climate scenarios are expected to decrease. The majority of the 10-year and 100-year return periods of floods in 2020-2049 and 2070-2099 increase; however 10-year and 100-year return periods for droughts tend to decrease.