<p>We employ a partially saturated groundwater modeling sensitivity analysis to investigate slope instability and landslides due to flood irrigation in the Siguas River Valley of the Majes Irrigation Project region in Peru. Using this approach, we test the hypothesis that flood irrigation practices created a perched water table, and that this perched water table significantly impacts slope stability. We then used our modeling approach to explore how intentional modifications to the topsoil’s hydraulic conductivity, such as those from biochar amendment, impact timing of slope failure. Our modeling approach demonstrates the importance of hydraulic conductivity on slope failure and that modest increases in soil hydraulic conductivity could extend the time to failure for nearby slopes by up to 2 years. Additional simulations predict that a 12% increase in hydraulic conductivity, which could be achieved through biochar amendment to the soil combined with a 25% reduction in irrigation volume, could stabilize slopes for up to 6.87 years longer than without mitigation, while still maintaining sufficient near-surface water to support agricultural productivity. Our findings are directed at the Majes region, while also demonstrating a novel approach to applying biochar amendments to help balance irrigation needs, agricultural productivity, and slope stabilization in vulnerable and/or arid environments.</p>