Investigating the impacts of plant-physiological responses to rising CO2 on future flood risk using hydrodynamic downscaling of Earth system model results to assess changes in return period, inundated area, and exposure on global-scales

Authors: Megan Fowler, University of California, Irvine, James Randerson, University of California, Irvine, Gabriel Kooperman*, University of Georgia, Michael Pritchard, University of California, Irvine
Topics: Global Change, Climatology and Meteorology, Hazards, Risks, and Disasters
Keywords: Climate Change, Earth System Modeling, Flooding, Plant Physiology, Community Earth System Model
Session Type: Paper
Day: 4/12/2018
Start / End Time: 1:20 PM / 3:00 PM
Room: Napoleon B3, Sheraton 3rd Floor
Presentation File: No File Uploaded

Climate change is expected to increase the frequency of intense river flooding events, and thus the risk of flood-related mortality, infrastructure damage, and economic loss. While precipitation intensity is a large driver of increased flooding, assessments from Earth system models based only on precipitation changes neglect important processes that occur within the land-surface, particularly the impacts of plant-physiological responses to rising CO2. As the CO2 concentration increases, plants may respond by reducing their stomatal openings, which can decrease water lost through transpiration and maintain higher soil moisture levels. For a given precipitation rate, elevated soil moisture can increase runoff intensity by limiting rainwater surface infiltration.

Here we assess the relative impacts of plant-physiological and radiative-greenhouse responses to increasing CO2 on changes in extreme runoff intensity using the Community Earth System Model. We further apply hydrodynamic downscaling using the CaMa-Flood model to assess changes in flood return period, inundated area and exposure. We find that plant-physiological effects contribute to only a small increase in precipitation intensity, but are a dominant driver of runoff intensification, contributing to half of the 99th percentile runoff intensity change. Hydrodynamic downscaling of global-scale daily runoff reveals that both the radiative and physiological responses to climate change contribute significantly to future changes in flood return period, inundated area and number of people exposed. Our results imply that constraining the sensitivity of stomatal responses to increasing CO2 is of first order importance to reducing uncertainty for potential river-flooding frequency and associated risk in a changing climate.

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