Historical Trends in Mean and Extreme Runoff and Streamflow Based on Observations and Climate Models

Behzad Asadieh,Nir Krakauer,Balázs Fekete

doi:10.3390/w8050189

Behzad Asadieh, Nir Krakauer + Show 1 more

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https://doi.org/10.3390/w8050189

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Journal: Water	Publication Date: May 7, 2016
Citations: 27	License type: CC BY 4.0

Affiliation: City College of New York, City University of New York

Abstract

To understand changes in global mean and extreme streamflow volumes over recent decades, we statistically analyzed runoff and streamflow simulated by the WBM-plus hydrological model using either observational-based meteorological inputs from WATCH Forcing Data (WFD), or bias-corrected inputs from five global climate models (GCMs) provided by the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP). Results show that the bias-corrected GCM inputs yield very good agreement with the observation-based inputs in average magnitude of runoff and streamflow. On global average, the observation-based simulated mean runoff and streamflow both decreased about 1.3% from 1971 to 2001. However, GCM-based simulations yield increasing trends over that period, with an inter-model global average of 1% for mean runoff and 0.9% for mean streamflow. In the GCM-based simulations, relative changes in extreme runoff and extreme streamflow (annual maximum daily values and annual-maximum seven-day streamflow) are slightly greater than those of mean runoff and streamflow, in terms of global and continental averages. Observation-based simulations show increasing trend in mean runoff and streamflow for about one-half of the land areas and decreasing trend for the other half. However, mean and extreme runoff and streamflow based on the GCMs show increasing trend for approximately two-thirds of the global land area and decreasing trend for the other one-third. Further work is needed to understand why GCM simulations appear to indicate trends in streamflow that are more positive than those suggested by climate observations, even where, as in ISI-MIP, bias correction has been applied so that their streamflow climatology is realistic.

Highlights

Anthropogenic changes in global climate and alteration of Earth’s hydrological cycle [1,2,3] have resulted in increased heavy precipitation with consequent increased surface runoff and flooding risk [4,5], which is likely to worsen in the future [6]
Further work is needed to understand why global climate models (GCMs) simulations appear to indicate trends in streamflow that are more positive than those suggested by climate observations, even where, as in Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP), bias correction has been applied so that their streamflow climatology is realistic
As a result of global warming, global climate models (GCMs) and satellite observations both indicate that atmospheric water vapor content has increased

Summary

Introduction

Anthropogenic changes in global climate and alteration of Earth’s hydrological cycle [1,2,3] have resulted in increased heavy precipitation with consequent increased surface runoff and flooding risk [4,5], which is likely to worsen in the future [6]. As a result of greenhouse gas (GHG) build-up in the atmosphere, global mean near-surface temperature shows an increasing trend since the beginning of the 20th century [11,13,14]. Assessment Report of Inter-Governmental Panel on Climate Change (IPCC) indicates that global land and ocean near-surface air temperature has increased by approximately 0.78 ̋ C, over the 20th century, with greater trend slope in recent decades [15]. Increasing availability of moisture in the atmosphere can be expected to result in increased intensity of extreme precipitation [1,5,7,8,18], with proportionally greater impact than for mean precipitation [17,19]. In terms of mean precipitation, some studies suggest that moist regions become wetter and dry regions drier [3,18,28,29], while some recent studies challenge this concept [30]

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