Influence of Natural and Human Drivers on Global and Regional Hydroclimate Changes

The hydroclimate is governed by a complex interplay of natural and human factors. Over the last millennium, natural forcing agents, like solar variability or volcanic activity, superimposed to purely generated oceanic oscillations, have been the primary drivers of hydroclimate variability. However, since the industrial revolution, human activities, particularly the emissions of greenhouse gases generated by burning fossil fuels, and of aerosols from industrial pollution, have become the dominant forcing agents, leading to unprecedented changes in both global and regional hydroclimate. Human-driven climate change is expected to alter mean precipitation patterns, intensify extreme weather events, and thereby increase floods, landslides with significant threats to water resources, infrastructure, and agriculture.

Previous analyses have demonstrated that the gradual rise in greenhouse gas emissions and the uneven spatial distribution of aerosol emissions have already impacted observed hydroclimate changes through emerging mechanisms. In this study, we utilize various datasets of daily precipitation, ecological reconstructions from lake sediments, and a wide array of CMIP6 climate simulations to examine the effects of natural and human influences on past and historical hydroclimate changes. For example, we explored the underlying causes of recent global changes in extreme rainfall events, employed statistical and machine learning techniques to disentangle between unforced and forced components in extreme rainfall, and identified unprecedented, forced changes in the climate and aquatic ecosystems of the Earth's Third Pole.

This work was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and funded by the DOE RGMA Program (PCMDI Scientific Focus Area).