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The semiarid rangelands production shows a randomized pattern, following rainfall, characterizing high risk of low biomass production and high variation coefficient (43,2%) of this production. To minimize this oscillatory pattern of primary production as well as the secondary production, the nopal cactus with its CAM metabolism and its high water use efficiency should be used. So, to simulate the rainfall variability and its effect on nopal cactus, a greenhouse study was carried out in the semiarid region of Northeast Brazil. After the establishment of a mathematic relation between rainfall and biomass, using historical data of the region, the response pattern of nopal cactus along 39 years were compared to the response pattern of the rangeland. After estimating the forage biomass of nopal cactus and rangeland, the Monte Carlo approach was applied, estimating the risk of biomass production below 1.0 Mg ha-1 ano-1, its maximum and minimum values, as well as the associated variation coefficients. The nopal cactus and rangeland estimated biomass production averaged 17147�3869 and 4352�1841kg/ha x year, with minimum and maximum values from 8663 to 23888 and from 0 to 6170kg/ha x year and a variation coefficient of 22.7 and 42.3%, respectively. The results showed that the minimum value (8663 kg) to nopal cactus is twice of the rangeland estimated biomass (4.352 kg), ameliorating he negative effects of low rainfall years. The biomass production variation coefficient was reduced from 42.3 to 22.7% by using nopal cactus as a complementary resource, enhancing the resilience of the production system. As a consequence, the feed availability, the animal production and the revenue were regularized, making the animal production in semiarid areas more sustainable.