This review by Susanne Schwinning and Osvaldo E. Sala explores the hierarchy of responses to resource pulses in arid and semi-arid ecosystems. The authors argue that short periods of high resource abundance, often triggered by rainfall events, can lead to a series of ecological responses that vary in magnitude and duration. They propose a framework where small pulses trigger minor ecological events, while larger pulses elicit more significant and widespread responses. The review discusses how precipitation, climate, and site factors translate into soil moisture pulses of varying sizes and durations, and how these pulses influence the physiological and ecological activities of different organisms. Key points include the importance of pulse depth and duration, the role of response thresholds, and the potential evolutionary background for these thresholds. The authors also consider the implications of climate change on the hierarchical organization of ecosystem responses to precipitation events, suggesting that this framework may provide new insights into the future of arid and semi-arid lands.This review by Susanne Schwinning and Osvaldo E. Sala explores the hierarchy of responses to resource pulses in arid and semi-arid ecosystems. The authors argue that short periods of high resource abundance, often triggered by rainfall events, can lead to a series of ecological responses that vary in magnitude and duration. They propose a framework where small pulses trigger minor ecological events, while larger pulses elicit more significant and widespread responses. The review discusses how precipitation, climate, and site factors translate into soil moisture pulses of varying sizes and durations, and how these pulses influence the physiological and ecological activities of different organisms. Key points include the importance of pulse depth and duration, the role of response thresholds, and the potential evolutionary background for these thresholds. The authors also consider the implications of climate change on the hierarchical organization of ecosystem responses to precipitation events, suggesting that this framework may provide new insights into the future of arid and semi-arid lands.