Global change in streamflow extremes under climate change over the 21st century

Abstract

Abstract. Global warming is expected to intensify the Earth's hydrological cycle and increase flood and drought risks. Changes over the 21st century under two warming scenarios in different percentiles of the probability distribution of streamflow, and particularly of high and low streamflow extremes (95th and 5th percentiles), are analyzed using an ensemble of bias-corrected global climate model (GCM) fields fed into different global hydrological models (GHMs) provided by the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) to understand the changes in streamflow distribution and simultaneous vulnerability to different types of hydrological risk in different regions. In the multimodel mean under the Representative Concentration Pathway 8.5 (RCP8.5) scenario, 37 % of global land areas experience an increase in magnitude of extremely high streamflow (with an average increase of 24.5 %), potentially increasing the chance of flooding in those regions. On the other hand, 43 % of global land areas show a decrease in the magnitude of extremely low streamflow (average decrease of 51.5 %), potentially increasing the chance of drought in those regions. About 10 % of the global land area is projected to face simultaneously increasing high extreme streamflow and decreasing low extreme streamflow, reflecting the potentially worsening hazard of both flood and drought; further, these regions tend to be highly populated parts of the globe, currently holding around 30 % of the world's population (over 2.1 billion people). In a world more than 4 • warmer by the end of the 21st century compared to the pre-industrial era (RCP8.5 scenario), changes in magnitude of streamflow extremes are projected to be about twice as large as in a 2 • warmer world (RCP2.6 scenario). Results also show that inter-GHM uncertainty in streamflow changes, due to representation of terrestrial hydrology, is greater than the inter-GCM uncertainty due to simulation of climate change. Under both forcing scenarios, there is high model agreement for increases in streamflow of the regions near and above the Arctic Circle, and consequent increases in the freshwater inflow to the Arctic Ocean, while subtropical arid areas experience a reduction in streamflow.

Recent trends in the frequency and duration of global floods

“…Three flow exceedance thresholds (Q * ) as the 90th, 95th, and 99th percentile of the entire daily streamflow time series are calculated for each station separately. These thresholds for flood definition are consistent with earlier studies on this subject (e.g., Wu et al, 2012Wu et al, , 2014Koirala et al, 2014;Asadieh and Krakauer, 2017).…”

Sensitivity of Regulated Streamflow Regimes to Interannual Climate Variability

“…Selected structures are distributed throughout the Central-Eastern United States, where climate changes have induced an enhanced likelihood of floods/droughts and an increased interseasonal imbalance of water availability (Easterling et al, 2000;Groisman et al, 2004;IPCC, 2014;Mallakpour & Villarini, 2015;Melillo et al, 2014). In this region, modest discharges typical of summer and fall seasons have been reducing due to larger evapotranspiration losses and earlier snowmelt, while abundant streamflows during winter and spring are observed more frequently as a consequence of increased precipitation (Asadieh & Krakauer, 2017;Carter et al, 2014;Horton et al, 2014;Pryor et al, 2014;Schafer et al, 2014).…”

Changes in the exposure of California’s levee-protected critical infrastructure to flooding hazard in a warming climate

“…However, numerous studies in recent years contradicted with the stationary assumption and showed that changes in climate are anticipated to alter the characteristics of flooding events (e.g. Barnett et al 2005, Kundzewicz et al 2014, Asarian and Walker 2016, Asadieh and Krakauer 2017, Ehsani et al 2017, Najibi et al 2017. For instance, (Das et al 2013) projected about 30%-100% increase in the magnitude of annual maximum streamflow over California.…”