This study aimed to analyze how, when and how changes in soil use and vegetation cover
influenced the hydrological behavior of the Itacaiúnas river watershed (IRW), Eastern
Amazonia, during the last 40 years (1973-2013). The main land use and cover changes in the
basin in this period were the significant reductions in native forest, marked increase in pasture
area and growth in urban areas. Considering the need to quantify the main inputs
(precipitation) and outflows (flow) of the basin's water balance, an estimation of precipitation
and average flows for the basin was made, which is Manuscript 1 accepted for publication by
the Brazilian Journal of Physical Geography (RBGF). In this paper the relationship between
observed precipitation data from seven meteorological stations and those resulting from
interpolation performed by the Climate Prediction Center (CPC) in the period 1986-2005 was
analyzed. Using the methods of correction by the drainage area and standardization of
medium flows, the estimated flows were compared with measured flows (1985-1995). The
precipitation results were compatible with the seasonal behavior of the region, whose
correlation between observed and interpolated data showed that these represent well the
space-time variability of precipitation in the IRW. It was observed a tendency of increase in
the precipitation from east to west, whose behavior may be associated with dense forest cover
that composes the mosaic of Conservation Units (UC's), combined with high altitudes (600-
800 m) of Serra de Carajás. The analysis of the calculated flows showed results consistent
with the seasonal behavior of the flow curves within the hydrological year. Although the
methods used presented different results in absolute terms, the calculated flow curves follow
the behavior of the measured flow curve. In Manuscript 2, Three decades of reference
evapotranspiration estimate for a watershed in the Eastern Amazon, accepted for publication
in the Annals of the Brazilian Academy of Sciences (ABC), the reference evapotranspiration
rate (ETo) for the basin was estimated and the accuracy of eight empirical equations using
monthly data (1980-2013). The Turc and Penman-Monteith methods showed the best results.
Solar radiation and average temperature are shown to be the main drivers, while relative
humidity and wind speed have a much smaller impact. The temporal and spatial variability
presents strong stationarity, increase in the dry period and decrease in the wet period.
Statistical analysis indicated that there is no correlation between station waste and that
physical parameters explain ETo variations. Finally, the 3rd Manuscript, in the final phase of
preparation, presented the water balance response to changes in soil use and cover in the
eastern Amazon during the last three decades. In this paper, soil texture maps combined with
soil use classes in each decade were estimated, estimating the values of CN (Curve Number),
soil water storage (S) and storage variation (ΔS). The behavior of the water balance
components {Precipitation (P), Potential Evapotranspiration (Eo), Real Evapotranspiration
(E) and ΔS} due to changes in soil use and vegetation cover were analyzed according to the
Budyko model, at annual and as a function of seasonal aridity and evaporative indices.
Seasonal values were aggregated to quantify the interannual variability of changes in
evaporation and storage. The seasonality of rainfall and the seasonal dynamics of storage
were directly incorporated into the developed model, which allowed us to understand which
are the dominant control factors on the water balance. In the last decade (2013) the remaining
forest cover is only 48.91%, in turn, the cover formed by pasture is 50.47%. The capacity of
water storage in the soil decreases continually reaching 8.1%. The results show an
approximately linear tendency whose points exceed the "water limit" (Eo / P> 1) and execute
the "energy limit", representing dry years with higher values of PE / (P - ΔS), in which annual
soil storage provides a complementary supply for annual E. Although the IRW does not fit
into a situation of low water availability, its pedological and storage capacity characteristics
indicate an increasing trend in flow rates (CN> 72) and low capacity to store water.
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