Local climate determines the NDVI-based primary productivity and flooding creates heterogeneity in semi-arid floodplain ecosystem

Water is clearly the key driver of ecosystem functioning in arid and semi-arid floodplain environment. Both local rainfall and overbank flow contribute to water accessible by a plant. Variability in rainfall and hydrological regimes at seasonal and longer time scales exerts strong influences shaping ecosystem structure and function in arid and semi-arid floodplains. Yet there are few studies exploring how the interplay of climatic and hydrologic factors affects the integrity of floodplain ecosystems, especially the intermittently flooded vegetated wetlands. In fact, the importance of hydrological regimes prevailingly dominates the literature on floodplain ecology. Consequently, re-establishing and maintaining hydrological regimes has become the cornerstone underpinning most large scale floodplain conservation and restoration programs. In this study, we quantified the relative contribution of climatic and hydrologic variables to ecosystem functioning in the generalized additive modelling (GAM) framework using indicators derived from time series of MODIS 250 m NDVI (Normalized Difference Vegetation Index). Results from the “best fitted” GAM models reveal that local rainfall has a closer and more important relationship with wetland mean NDVI (a surrogate of system primary productivity) although the co-variability between primary productivity and inflow is significantly positive. On the other hand, inflows play a dominant role in creating and maintaining the spatial heterogeneity represented by standard deviation of wetland NDVI while local rainfall has an opposite effect. Further, different vegetation community types exhibit distinct seasonality patterns in the NDVI-based primary productivity. These results illustrate the complexity of interactions between vegetation type, climate variations, and hydrology in floodplain wetlands. These results also demonstrate the sensitivity of floodplain wetlands to the perturbations in rainfall and temperature regimes, which would be more intense under the projected climate change.

► We investigated the impacts of interplay of climate and hydrology on floodplain with GAM.
► We found that climate played principal role in NDVI-based productivity.
► We found that the most important role of hydrology was creating productivity heterogeneity.