Vegetation fires are the second largest source of greenhouse gas emissions to the atmosphere. The reduction of the climatic impact of these emissions is related to the vegetation susceptibility to fire (fire risk), as well as to the understanding of possible implications of changes in atmospheric circulation on fire risk in the nearfuture. This study evaluates the environmental susceptibility to fire occurrence based on a Potential Fire Index (PFI). Two climate simulations from the ECHAM5/MPI-OM climate model have been used to calculate the PFI: present day and an experiment for the end of the twenty-first century (2080-2100). The results indicate that the proposed PFI methodology could properly reproduce the areas with the highest fire incidence under present conditions. Moreover, it was found that under greenhouse warming conditions the PFI foresees an increase in the fire risk area, particularly for the Amazon region. We concluded, furthermore, that changes of vegetation predicted to occur in the future lead to substantial modifications in the magnitude of the PFI, and may potentially extend the length of the fire season due to induced longer drought periods as compared to current conditions.
Drought is a natural hazard with critical societal and economic consequences to millions of people around the world. In this paper, we present the climatology of severe drought events that occurred during the 20th century in the region of Sao Paulo, Brazil. To account for the effects of rainfall deficit and changes in temperature at a climatic timescale, we chose the Standardized Precipitation Evapotranspiration Index (SPEI) to identify severe droughts over the city of Sao Paulo, and the eastern and central-western regions of the state. Events were identified using weather station data and European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis data, in order to assess the representation of drought periods in both datasets. Results show that the reanalysis seems suitable to represent the number of events and their mean duration, severity and intensity, but the timing and characteristics of individual events are not well reproduced. The correlation between observation and reanalysis SPEI time series is low to moderate in all cases. A linear trend analysis between 1901 and 2010 shows a tendency of increasing (decreasing) severe drought events in the central and western (eastern) Sao Paulo state, according to observational data. This is in agreement with previous findings, and the reanalysis presents this same signal. The weakened trend values in the reanalysis may be associated with issues in representing precipitation in this dataset.
This study investigates the anomalous patterns of the oceanic and atmospheric heat transport, transient waves and the interaction between transient waves and the mean zonal flow. The evaluation is based on simulations performed with a coupled model forced by an increase of 1 Sverdrup of freshwater flux into the North Atlantic Ocean. It is found that an increase of freshwater flux in the North Atlantic leads to a weakening in the Northern Hemisphere (NH) oceanic heat transport by up to 1 Petawatt (10 15 ) PW but results in an intensification of the Southern Hemisphere (SH) total heat transport. This inter-hemispheric seesaw leads to substantial changes in transient wave activity which is associated with anomalous meridional temperature flux and eddy kinetic energy (EKE). During winter in the NH, weakening of the thermohaline circulation induces an increase in the storm track activity. However, a reduction in storm tracks is found over the extratropical regions of the SH. The correspondence between the anomalies of storm track intensity and Eady growth rate lead to the conclusion that changes in the transient eddy activity are mostly generated by changes in baroclinic conditions. Furthermore, calculations of the E vector show that interaction between transient and mean flow is most pronounced over the North Atlantic where stronger storm tracks enhance the mean westerlies, thus minimising the effect of changes in the oceanic heat transport.
The wind stress is a measure of momentum transfer due to the relative motion between the atmosphere and the ocean. This study aims to investigate the anomalous pattern of atmospheric and oceanic circulations due to 50% increase in the wind stress over the equatorial region and the Southern Ocean. In this paper we use a coupled climate model of intermediate complexity (SPEEDO). The results show that the intensification of equatorial wind stress causes a decrease in sea surface temperature in the tropical region due to increased upwelling and evaporative cooling. On the other hand, the intensification of wind stress over the Southern Ocean induces a regional increase in the air and sea surface temperatures which in turn leads to a reduction in Antarctic sea ice thickness. This occurs in association with changes in the global thermohaline circulation strengthening the rate of Antarctic Bottom Water formation and a weakening of the North Atlantic Deep Water. Moreover, changes in the Southern Hemisphere thermal gradient lead to modified atmospheric and oceanic heat transports reducing the storm tracks and baroclinic activity.
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