This study builds long-anticipated bridges between the literature on (i) climate/disaster security, (ii) women, peace, and security, and (iii) rebel group behavior. Specifically, I analyze how rebel groups react to disasters (like droughts, earthquakes, floods, or storms) by intensifying or reducing their armed activities. This addresses a crucial knowledge gap: While a large literature is dealing with the impacts of climate change and disasters on armed conflict onset or incidence, knowledge on how environmental factors shape the behavior of particular conflict actors remains scarce. I argue that rebel groups escalate fighting when disaster-related opportunities occur (e.g., easier recruitment) but scale back their armed activities if adversely affected by the disasters (e.g., loss of resources). However, this relationship is contingent of the rebels’ inclusion of female combatants. Empirically, this study draws on a unique sample of thirty-six cases of disasters striking armed conflict zones and integrates quantitative and qualitative data via a qualitative comparative analysis. The results suggest that rebel groups intensify their armed activities to exploit disaster-related opportunities but can only do so when female combatants provide them with sufficient capabilities. Conversely, rebels have to reduce fighting when adversely affected by disasters unless they can draw on female members to cope with disaster impacts.