Continental-scale impacts of intra-seasonal rainfall variability on simulated ecosystem responses in Africa

[摘要] Climate change is expected to modify intra-seasonal rainfall variability,arising from shifts in rainfall frequency, intensity and seasonality. Theseintra-seasonal changes are likely to have important ecological impacts onterrestrial ecosystems. Yet, quantifying these impacts across biomes andlarge climate gradients is largely missing. This gap hinders our ability tobetter predict ecosystem services and their responses to climate change, especiallyfor arid and semi-arid ecosystems. Here we use a synthetic weather generatorand an independently validated vegetation dynamic model (SEIB-Dynamic Global Vegetation Model, DGVM) tovirtually conduct a series of "rainfall manipulation experiments" to studyhow changes in the intra-seasonal rainfall variability affect continent-scaleecosystem responses across Africa. We generate different rainfall scenarioswith fixed total annual rainfall but shifts in (i) frequency vs. intensity,(ii) rainy season length vs. frequency, (iii) intensity vs. rainy seasonlength. These scenarios are fed into SEIB-DGVM to investigate changes inbiome distributions and ecosystem productivity. We find a loss of ecosystemproductivity with increased rainfall frequency and decreased intensity atvery low rainfall regimes (<400 mm year⁻¹) and low frequency(<0.3 event day⁻¹); beyond these very dry regimes, most ecosystemsbenefit from increased frequency and decreased intensity, except in the wettropics (>1800 mm year⁻¹) where radiation limitation preventsfurther productivity gains. This result reconciles seemingly contradictoryfindings in previous field studies on the impact of rainfallfrequency/intensity on ecosystem productivity. We also find that changes inrainy season length can yield more dramatic ecosystem responses compared withsimilar percentage changes in rainfall frequency or intensity, with thelargest impacts in semi-arid woodlands. This study demonstrates thatintra-seasonal rainfall characteristics play a significant role ininfluencing ecosystem function and structure through controls onecohydrological processes. Our results suggest that shifts in rainfallseasonality have potentially large impacts on terrestrial ecosystems, andthese understudied impacts should be explicitly examined in future studies ofclimate impacts.

[学科分类] 地球化学与岩石