Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models

Y Wang,R Gallimore,J E Kutzbach,M Notaro,Z Liu,S Levis

doi:10.5194/cp-4-59-2008

Abstract

Abstract. Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte-Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.

Highlights

2006a, Notaro et al, 2006 for detailed methodology), we present a negative vegetation-precipitation feedback at the annual timescale from two mid-Holocene simulations with Fast Ocean Atmosphere Model (FOAM) (Gallimore et al, 2005), and CCSM2 (Levis et al, 2004a), both of which are coupled with the Lund-PotsdamJena Dynamic Global Vegetation Model (LPJ-DGVM, Sitch et al, 2003)
We have presented three important findings with two fullycoupled atmosphere-ocean-land surface-vegetation climate model simulations in the mid-Holocene
A negative feedback between vegetation and precipitation mainly occurs in the mid-Holocene, when the overall climate and soil are wetter and darker than pre-industrial and present-day conditions

Summary

Introduction

2006a, Notaro et al, 2006 for detailed methodology), we present a negative vegetation-precipitation feedback at the annual timescale from two mid-Holocene simulations with FOAM (Gallimore et al, 2005), and CCSM2 (Levis et al, 2004a), both of which are coupled with the Lund-PotsdamJena Dynamic Global Vegetation Model (LPJ-DGVM, Sitch et al, 2003). In the meantime of this research, Notaro et al (2008) conducted a statistical and dynamical assessment of simulated vegetation-rainfall interactions in mid-Holocene North Africa with foci on the FOAM model. Compared with the study of Notaro et al (2008), we present here the detailed results from two mid-Holocene equilibrium simulations in fully coupled climate models (FOAM and CCSM2). Our result further expands the findings of Notaro et al (2008) in that we report the timescale-dependence of the estimated vegetationprecipitation feedbacks, which, to our best knowledge, has not been reported before in vegetation and paleoclimate researches

Model description and experimental design

Outline of methodology

Results

Concluding remarks