How do variations in the temporal distribution of rainfall events affect ecosystem fluxes in seasonally water-limited Northern Hemisphere shrublands and forests?

I Ross,R L Scott,A Cescatti,L Genesio,A Arneth,L Misson,S Rambal,A Carrara

doi:10.5194/bg-9-1007-2012

Abstract

Abstract. Rainfall regimes became more extreme over the course of the 20th century, characterised by fewer and larger rainfall events. Such changes are expected to continue throughout the current century. The effect of changes in the temporal distribution of rainfall on ecosystem carbon fluxes is poorly understood, with most available information coming from experimental studies of grassland ecosystems. Here, continuous measurements of ecosystem carbon fluxes and precipitation from the worldwide FLUXNET network of eddy-covariance sites are exploited to investigate the effects of differences in rainfall distribution on the carbon balance of seasonally water-limited shrubland and forest sites. Once the strong dependence of ecosystem fluxes on total annual rainfall amount is accounted for, results show that sites with rainfall distributions characterised by fewer and larger rainfall events have significantly lower gross primary productivity, slightly lower ecosystem respiration and consequently a smaller net ecosystem productivity.

Highlights

During the 20th century, precipitation intensity and the frequency of large rainfall events increased (Easterling et al, 2000; Trenberth, 2011)
Because the rate of increase of gross primary productivity (GPP) with total rainfall amount is greater than the rate of increase of RE, net ecosystem productivity (NEP) increases with total rainfall amount (Fig. 2c)
Negative correlations are observed between ecosystem flux residuals and rainfall intensity: regressions between standardised ecosystem flux residuals and ZI are significant at the 5 % level for GPP for all sites together and for “dry” sites and “wet” sites alone, and for RE, for all sites together and for “wet” sites

Summary

Introduction

During the 20th century, precipitation intensity and the frequency of large rainfall events increased (Easterling et al, 2000; Trenberth, 2011). Anthropogenic climate change is expected to intensify this shift towards fewer, larger rainfall events (Trenberth et al, 2003). While the impacts of differences in total rainfall amount on terrestrial ecosystem productivity have been studied for a range of ecosystems and climate regions (Wu et al, 2011; Huxman et al, 2004b), the ecological implications of changes in the temporal structure of rainfall, i.e. a shift towards fewer and larger rainfall events, have received less attention; results have so far been inconclusive (Jentsch et al, 2007). Despite the potential impact of changes in temporal patterns of rainfall distribution on shrublands and forests, data for these ecosystems is sparse.

Methods

Results

Discussion

Conclusion