The climatic growth index (ICC) for forage grasses, based on temperature, solar radiation and the ratio of actual to potential evapotranspiration, was used to estimate dry matter production (TAMS) for the following grasses: "colonião" (Panicum maximum Jacq), "gordura" (Melinis minutiflora Pal de Beauv), "jaraguá" (Hyparrhenia rufa (Ness) Stapf) and "pangola" (Digitaria pentzii Stent), using exponential equations: ICC = a EXP (b ICC), where a and b are constants which differ for each specie analised. The monthly mean climatic index was calculated for forty seven localities of the State of São Paulo and neighbours. Its spatial distribution considering summer and winter is shown as maps. ICC values during the critical season of the winter varied from 0.1 to 0.15 for the central part of the State; at the northern and western regions it is larger than 0.15 and at the "Mantiqueira" mountains it is less than 0.1.
climatic growth index; forage grasses