Land cover change drives climate extremes and aridity in non-Amazonian South America

Abstract:

Increasing evidence is showing the relevance of land cover change on the regional mean climate. However, the mechanisms that explain these interactions remain a challenge in land – atmosphere interactions science. This challenge is particularly significant in understanding the role of vegetation change on climate extremes and aridity, which has been barely addressed by the literature.

In this paper we focus on this gap by investigating the effects of land use and land cover change on selected climate extremes indices and aridity in non-Amazonian South America over an area of about 3 million km². We run a 3 ensemble climate model nudged with the ERA-Interim reanalysis and stretched to 25 km resolution for present (year 2005) land cover relative to realistic historic vegetation distribution. The most important results of this experiment are that the degree of change in vegetation structure determines whether extreme daytime temperatures will increase or decrease, particularly during the dry season. This is because a large change in surface roughness promotes increased wind speeds and heat advection, whereas a small change in surface roughness does not increase wind and can increase heat build-up in the atmosphere since the sensible heat flux also increases. We also put these results in a wider context of land surface – atmospheric feedbacks by looking at the corresponding change in aridity (precipitation / potential evapotranspiration). This shows the processes that drive the changes in temperature extremes also determine whether significant changes in aridity occur, since all the change in aridity can be prescribed to changes in potential evaporation, or atmospheric water demand.

We propose a conceptual model of the mechanisms that explain these alterations which is an advance in understanding land-atmosphere interactions and provides evidence of the main mechanisms responsible of changes in the feedbacks because of changes in natural vegetation.