Rainfall and rain pulse role on energy, water vapor and CO2 exchanges in a tropical semiarid environment

•Seasonality and annual values of the energy balance and CO2 exchange components are closely related to rainfall variability.•Evaporative stress index (ESI) can reach values of extreme water stress during the dry season.•Rain pulses caused systematic increases in Gs and higher CO2 absorption. Several aspects of the hydrological regime influence the CO2 exchanges between the atmosphere and drylands. The objective of this study was to carry out a thorough assessment of the role of rainfall pulses on the energy fluxes, water vapor and CO2 exchanges over the Caatinga Biome using data collected in 2014 and 2015. We conducted an unprecedented analysis on the effects of precipitation pulses on the different components of the CO2 balance between the Caatinga and the atmosphere. Data was collected in a flux tower equipped with an eddy covariance system in a preserved Caatinga area in Northeast Brazil. Results showed a well defined relationship between rainfall variability and energy balance and CO2 exchange. Rain pulses caused systematic increases in surface conductance (Gs), leading to a higher CO2 absorption in the short-term. In 2014, the higher amount of rain pulse events along with higher overall rainfall amounts resulted in 68 % of total absorbed CO2 being assimilated during post-pulse events. In 2015, fewer but more intense pulses occurred, contributing to 39 % of total CO2 absorbed in the wet season. The overall effect of rain pulses on the CO2 balance over the Caatinga site in the Semiarid Brazil depends on the distribution and amount of rainfall in each pulse event.