Technical Abstract: In semiarid regions rainfall pulses provide intermittent opportunities for biological activity. These pulses have been shown to affect the activity of microbes and plant differently, altering the net ecosystem exchange of carbon dioxide (NEE) from these ecosystems. We examine NEE and its components of ecosystem respiration and photosynthesis for characteristic pulse responses using data from eddy covariance towers in regions with predominantly winter rainfall (Mediterranean) and summer rainfall (monsoonal). We then quantify these responses using simple pulse activation models to compare them across the disparate ecosystems and climate. Our results highlight how phenology interacts with precipitation seasonality, amount, and degree to which it can be stored in the soil to affect the pulse response of an ecosystem.