تغییر پذیری اقلیم در شمال شرق برزیل On climate variabilityin Northeast of Brazil

۱٫ Introduction Deforestation bycutting and burning, unsuitable use and soil degradation byman have reduced the quantityof water vapor that returns to the atmosphere byevapotranspiration process (Silva et al., 1998). Anthropogenic interference in the environment is one of the greatest causes of the process of climatic change in several regions of the world. This complex phenomenon, which includes natural and human processes, depends on a multiplicityof factors and is an almost irreversible scenario (Nimer, 1988). Climatic change results essentiallyfrom man’s action on the ecosystems that degrade veryquicklybut recover veryslowlyand lose biodiversity. Climatic change stronglyinfluences the process of desertification byits impact on the vegetation, soil and hydrological cycle (Pimenta et al., 1998). Currently, one of the great problems that affects humanityis the possibilityof a global climate change with unpredictable consequences on natural resources, especiallyon the qualityand quantityof potable water (OMM, 1992). Among the direct effects of climate change are changes in temperature, rainfall and wind speed (Schwalm and Ek, 2001). However, climate variabilityand climate change have been researched recentlybased on the analysis of different climatic variables. The most common are: class A pan evaporation (Balling and Brazel, 1987; Cohen et al., 2002); the aridityindex (Elagib and Abdu, 1997); and reference evapotranspiration (Hupet and Vanclooster, 2001; Kipkorir, 2002). Indeed, temperature and rainfall time-series are much used in climate variabilityanalysis (see e.g. Elagib and Mansell, 2000; Lazaro et al., 2001 ! ; Moonen et al., 2002; Morrison et al., 2002; Velichko et al., 2002). Recently, the climatic scenario projection for the future has also encouraged several investigations (Sefton and Boorman, 1997; Arnell, 1999; Chang, 2002; Lasch et al., 2002; Tao et al., 2002). The droughts that periodicallyaffect Northeast of Brazil are phenomenona that cause great social, economic and environmental impacts. The population of this region does not live satisfactorilywith the climatic instability, making the suffering from the drought a great problem in government policy. The main consequences of the droughts are related to low crop production and water supplyto the urban centers and rural communities. The atmosphere over Northeast of Brazil presents mean stabilityconditions that inhibit large-scale convective processes, caused bythe descending branch of the Walker circulation cell. The permanent South Atlantic anticyclone induces a mean situation of atmospheric stability. The disturbances from the east create instability and rain. A possible mechanism for the occurrence of severe droughts over Northeast of Brazil is the establishment of a thermallydirect local circulation which has its ascending branch at about 10
N and its descending branch over Northeast of Brazil and the adjoining oceanic region (Moura and Shukla, 1981). Some studies show that the sea-surface temperature anomalies of the Pacific and Atlantic oceans are associated with droughts in Northeast of Brazil (Moura and Shukla, 1981; Roucou et al., 1996). Manyinvestigators have studied climatic changes in various regions of the world including: United States (Balling and Brazel, 1987; Comrie and Broyles, 2002); Philippines (Jose et al., 1996); Bahrain (Elagib and Abdu, 1997); Europe (Arnell, 1999; Velichko et al., 2002); Kenya (Kipkorir, 2002); Arab Region (Abahussain et al., 2002); Taiwan (Chang, 2002; Yu et al., 2002); Israel (Cohen et al., 2002); and Italy (Moonen et al., 2002). On the other hand, Nimer (1988) and Silva et al. (1998) studied the problems of desertification and rainfall trends in Brazil, respectively. Thus, given the relevance of the climate change in the world, the present paper aimed to ascertain the occurrence of climatic variabilityin Northeast of Brazil, particularly in the semi-arid region.