Climate extremes, such as heat waves and heavy precipitation, are more likely to occur with increased warming and simultaneously have profound influences on ecosystem. More heat waves are expected to cause more droughts, while more heavy precipitation could cause more floods, and both may have a negative effect on vegetation growth, although wetter conditions may alternatively stimulate growth. Existing studies have already investigated how grassland ecosystems respond to a single extreme precipitation event and pulse effects of continuous rainfall events. However, the legacy effect of drought prior to the rainfall events, whether extreme events or multiple pulses, is generally ignored. Therefore, how ecosystems respond to consecutive drought and extreme rainfall is still not clear. The year 2006 was the third driest year in the southern Great Plains, with only 61% of long-term annual precipitation. In contrast, the summer of 2007 was the second-wettest summer, with 121% of the normal annual precipitation. This “pair” provides a unique example to study the impacts of alternatively contrasting climate extremes on semi-arid grassland ecosystems. In this study, we aim to assess whether or not this consecutive drought and flood has altered the sensitivity of ecosystem carbon fluxes (GPP) and rain use efficiency (RUE). We parameterize a newly developed process-based terrestrial ecosystem model (TEM-Hydro daily version) and apply the BCCA 1/8-degree daily climate datasets. The modeled results are compared against the MODIS datasets and Eddy Covariance observations to determine the mechanism responsible for understanding how legacy effects followed by extreme rainfall affect ecosystem functions.
Results/Conclusions
The preliminary results show that GPP increases with extreme precipitation while drought is ongoing, and RUE does not change with extreme precipitation, as the ecosystem is water limited. However, RUE and GPP of tall grassland ecosystems decrease non-linearly with extreme precipitation when floods occur, because extra water might be lost through surface runoff. We will compare current results with different starting conditions such as a normal year followed by an extreme wet year to different initial conditions.