The water balance of an Amazonian micro‐catchment: the effect of interannual variability of rainfall on hydrological behaviour

Abstract

Abstract:In humid tropical systems, the large intraseasonal and interannual variability of rainfall can significantly affect all components of the water balance. This variability and the lack of detailed hydrological and meteorological data in both temporal and spatial scales have created uncertainties regarding the closure of the water balance for the Amazon basin. Previous studies in Amazonian micro-catchments suggested that both the unsaturated and groundwater system, which are not taken into consideration in basin-wide water budgets published in the literature, play an important role in controlling the timing of runoff generation.In this paper, the components of the water balance and the variations in different storages within the system were examined using 3 years' data from a 6Ð58 km 2 micro-catchment in central Amazonia. The role and relative importance of the various stores were examined. The results show a strong memory effect in the groundwater system that carries over seasonal climate anomalies from one year to the next and affects the hydrological response well beyond the time span of the anomaly. In addition, the deep unsaturated zone was found to play a key role in reducing most of the intraseasonal variability and also affected the groundwater recharge. This memory effect is crucial for sustaining streamflow and evaporation in years with rainfall deficiency. The memory effect caused by storage in the groundwater and unsaturated systems may also prevent the closure of annual large-scale water balances, which assume that storage returns to a standard state each year.

The role of climatic and terrain attributes in estimating baseflow recession in tropical catchments

“…Although there were no good quality data to account for the effects of soil depth and aquifer porosity, deep soils and permeable regoliths are widely present in tropical landscapes; and are likely to represent an important source of baseflow (Chappell et al, 2007). A recent three-year study in a small catchment underlain by very deep soils in the central Amazon Basin by Tomasella et al (2008) showed an important contribution to the groundwater system by the extended unsaturated zone. Both unsaturated and groundwater flow showed a delayed response to rainfall and most of the seasonal variability in streamflow tended to be dampened by either one or the other.…”

Understory host plant and insect gall diversity changes across topographic habitats differing in nutrient and water stress in the Brazilian Amazon rainforest

“…The water table is at greater depths in the plateaus, and approaches the surface towards the bottom of the valleys (Tomasella et al 2007;Zanchi et al 2011). Likewise, there is an increasing content of sand in the soil from plateau to valleys, with a corresponding decrease in clay content.…”

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“…The installation of the drainage tubes therefore effectively lowered the phreatic level permanently by 0.23 m in the drained plot as compared to that in the control plot. Seasonality in the phreatic level is virtually absent in the riparian forest that is fed by a constant supply of deep groundwater originating from the plateau (Hodnett et al, 1997;Tomasella et al, 2008). However, due to the sandy, permeable nature of the soil, sudden drops can occur during dry periods, such as in October-November 2007 when the phreatic level in the control plot fell to a depth of 0.31 m below the surface in response to dropping groundwater levels on the plateau.…”

“…Riparian and ecotone campinarana forests grow on these poor sandy soils and experience almost permanently saturated soil conditions, which are maintained by a continuous flow of groundwater from slope and plateau areas, where higher groundwater levels are maintained by recharge during wet periods (Hodnett et al, 1997;Tomasella et al, 2008). Malhi and Phillips (2004) have reported that tropical forests are dynamic ecosystems of constantly shifting composition and structure.…”