The role of vegetation during the Argentine drought of 2008

OMAR V. MÜLLER; E. BERBERY

Workshop; WCRP Workshop on Drought Predictability and Prediction in a Changing Climate; 2011

This work focuses on the severe Argentine drought of 2008, that began in late 2007 and lasted until early 2009 and had strong socio-economic impacts. Extreme events over the region have often been linked to the sea surface temperature, specially to the El Niño/Southern Oscillation. However, as the drought progresses, surface processes affected by land  cover changes may have a local effect over heat fluxes which in turn may act as forcing in the overlying atmospheric states.To understand the contributions of land processes to the drought,  experiments with different land cover maps were  performed using long-term simulations with the regional Weather Reasearch and Forecasting Model (WRF) which has coupled the Noah land surface model. The experiments reveal that vegetation changes modify the spatial distribution of some properties like  green vegetation fraction, albedo, roughness length, stomatal resistance and others, and also the deeper ground conditions like root depth and soil moisture.  All these properties alter the latent heat and sensible heat fluxes at the boundary layer.The  drought began with a precipitation deficit due to remote forcings (e.g., a La Ni~na event was in progress), which by itself reduced the soil moisture in the region. Then, the drier soil favored increased  sensible heat flux and reduced  latent heat flux causing high temperatures,loss of vegetation and further depletion of rainfall, thus intensifying the dry conditions. This feedback between soil wetness and rainfall is better represented when the land surface model uses the most recent vegetation map and fields of sea surface temperature, green vegetation fraction and albedo that vary in time, suggesting that more realistic representation of land cover and their properties may contribute to improve the predictability of dry events.