Plant Physiological Responses to Rising CO₂ Modify Simulated Daily Runoff Intensity With Implications for Global‐Scale Flood Risk Assessment

Abstract

Climate change is expected to increase the frequency of flooding events and, thus, the risks of flood‐related mortality and infrastructure damage. Global‐scale assessments of future flooding from Earth system models based only on precipitation changes neglect important processes that occur within the land surface, particularly plant physiological responses to rising CO2. Higher CO2 can reduce stomatal conductance and transpiration, which may lead to increased soil moisture and runoff in some regions, promoting flooding even without changes in precipitation. Here we assess the relative impacts of plant physiological and radiative greenhouse effects on changes in daily runoff intensity over tropical continents using the Community Earth System Model. We find that extreme percentile rates increase significantly more than mean runoff in response to higher CO2. Plant physiological effects have a small impact on precipitation intensity but are a dominant driver of runoff intensification, contributing to one half of the 99th and one third of the 99.9th percentile runoff intensity changes.

Multimodel Analysis of Future Land Use and Climate Change Impacts on Ecosystem Functioning

“…One exception is a recent study by Kooperman et al (2018) who found that plant-physiological responses to a quadrupled CO 2 concentration are of similar importance for daily runoff extremes in the CESM ESM as radiative-induced precipitation changes. One exception is a recent study by Kooperman et al (2018) who found that plant-physiological responses to a quadrupled CO 2 concentration are of similar importance for daily runoff extremes in the CESM ESM as radiative-induced precipitation changes.…”

“…Several studies have investigated the drivers of changes in runoff, typically focusing on annual runoff. One exception is a recent study by Kooperman et al (2018) who found that plant-physiological responses to a quadrupled CO 2 concentration are of similar importance for daily runoff extremes in the CESM ESM as radiative-induced precipitation changes. Gedney et al (2006), using the MOSES land surface model, attributed the increase in global annual runoff observed over the twentieth century mainly to stomatal closure in response to increasing CO 2 .…”

Advances in understanding large‐scale responses of the water cycle to climate change

“…286 More efficient water use by plants can further cause increasing runoff responses to rainfall, particularly for extremes. 13,287,288 Precipitation and streamflow are also affected directly by human activities, and water use can offset and even dominate responses to climate change regionally. 289 Deforestation can drive increased streamflow as demonstrated by simulations and observations over the Amazon and East Africa, [290][291][292] although this can be counterbalanced by decreases resulting from irrigation.…”

Vegetation forcing modulates global land monsoon and water resources in a CO2-enriched climate

“…Unfortunately, no daily runoff output is available in the CMIP5 archive for the four ESMs used here. However a similar experiment with one model, CESM1-BGC, which followed the same protocol as the 1pctCO 2 experiments in CMIP5 40 (http://kooperman.uga.edu/grl2018/), does have daily runoff and precipitation. These CESM1-BGC simulations differ from CMIP5 by including extended periods of fixed preindustrial and 4×CO 2 conditions after the 1% per year ramp-up period, the first twenty-years of which are analysed here.…”