Positive impacts of precipitation intensity on monthly CO2 fluxes in North America

Precipitation is one of the most important climate factors that can affect the gross ecosystem production (GEP) of terrestrial ecosystems. Positive impacts of precipitation on annual GEP have been reported for vegetated areas worldwide. However, little is known about the influence of precipitation intensity on GEP, especially at the monthly to seasonal temporal scale. Here we show that monthly GEP is insensitive to the sum of monthly total precipitation (Ps, mm), but positively correlated to precipitation intensity (Pa, mm), defined as the average precipitation per event from half-hourly measurements over a month. Different plant functional types (PFTs) exhibit substantial differences in the sensitivity of monthly GEP to Pa. PFTs of water-limited regions responded more intensely than those in mesic environments, as demonstrated by a negative correlation between the slope of the GEP-Pa regression line and average Pa. Furthermore, this slope increases with latitude, indicating higher sensitivity of GEP to Pa for boreal ecosystems than for temperate regions. Therefore, we anticipate increased intensity of storms, as projected by some climate models, may impart a previously overlooked positive impact on precipitation intensity on GEP.