Erosivity and hydrological patterns of Hulha Negra, Rio Grande do Sul, Brazil, rainfalls in the period of 1956 to 1984

Abstract

The rainfall potential to cause water soil erosion is called rainfall erosivity. The objective of this study was to
determine the rainfall erosivity and hydrological patterns at Hulha Negra, RS, Brazil, based in the period 1956 to 1984, obtained from diary rainfall charts of FEPAGRO Meteorological Station. All of them were separated in individual rainfalls and from those were separated the erosive rainfalls and calculated the EI30 index and determined the hydrological pattern. The mean annual rainfall was 1239 mm relatively well distributed. The October to February period concentrates 61% of annual erosivity that coincides with soil tillage, seeding and growth of summer crops. The more notable peak
in the erosive potential occurs in February, when normally most of the crops already are in full growth. Another peak
occurs in April, consequence of exceptional rainfalls intensity at April of 1959. The less erosive rainfall potential occurs from May to August. In the average, the patterns advanced, intermediary and delayed has 53, 26 e 21% of erosive rainfalls per year, while these patterns correspond, respectively, to 60, 23 e 17% of the annual volume of erosive rainfalls, and 65, 22 e 13% of the mean annual rainfall erosivity. The annual index of erosivity for Hulha Negra is  6209 (MJ mm)/(ha h year), which can be used as “R” factor in the Universal Soil Loss Equation (USLE) to predict average annual soil loss by water erosion at Hulha Negra region. There were no significant relationship among rainfall coeficient (Rc) and the EI 30 index. However the obtained linear regression between this variable is adequate to estimate the “R” Factor for the counties surrounded Hulha Negra where only pluviometric records are availabe.