Importance of soil‐water to the Caatinga biome, Brazil

Abstract

Northeastern Brazil is hydrologically characterized by recurrent droughts leading to a highly vulnerable natural water resource system. The region contains the Caatinga biome, covering an area of approximately 800 000 km 2 . To increase insight in water balance components for this sparsely studied ecosystem, hydrology simulations were performed with the SWAP (Soil Water Atmosphere Plant) model for a Caatinga basin of 12 km 2 . SWAP model was developed to simulate hydrology under short-cycle crops, and its parameterization and validation to a diverse ecosystem is a novelty. The validation of the simulations was performed using a dataset of daily soil water content measurements taken at 0.2 m depth in three sites in the basin in the period from 2004 to 2012. Average Nash-Sutcliffe efficiency coefficient for these simulations was 0.57 and root mean square error of prediction was 4.3%. The results of the simulations suggest that water components do not diverge statistically among different sites of the biome. The Caatinga biome returns 75% (±17%) of the annual precipitation to the atmosphere, whereas the partitioning of total evapotranspiration into its components (transpiration, evaporation and interception) on annual basis accounts for 41% (±7%), 40% (±6%) and 19% (±3%) respectively. Regarding water availability, the surface soil layer (0.0-0.2 m) is the most important layer in the rooted profile, supplying up to 90% of atmospheric water demand. According to our analysis performed on daily basis, evapotranspiration and air temperature are most sensitive to soil moisture during the periods

Hydrology of a Water‐Limited Forest under Climate Change Scenarios: The Case of the Caatinga Biome, Brazil

“…Average annual rainfall is 518 mm, concentrated in the rainy season between January and May. The monthly average temperatures range from 24 • C to 28 • C. The watershed is covered by dense native vegetation characterized by tree heights typically between 5 and 12 m. More detailed information can be found in [10,16,17].…”

“…The water table is located several meters below the river bed, restraining its connection to the root zone, and rainfall is the main source of water for plant transpiration. Consequently, the Caatinga forest developed shallow roots to enhance root water uptake from upper soil layers [10,11]. Leaf shedding is the main characteristic and survival strategy to cope with up to nine months of the rainless season.…”

“…The Caatinga biome prevails as the main natural forest of this region, a complex tropical and water-limited ecosystem with a wide variety of both herbaceous and arborescent vegetation, characterized by its ability to cope with low soil water content ranges [10,11]. Recently predicted climate changes, assessed by indices from global and regional climate models, including consecutive dry days and soil moisture anomalies, have projected an increase in air temperature and the duration and intensity of drought in some large regions of the world.…”

Permanence of Water Effectiveness in the Root Zone of the Caatinga Biome

“…Recent research carried out in the Brazilian semi-arid region demonstrated the importance of the soil both in the surface flow initiation and as a water reservoir for vegetation (FIGUEIREDO et al 2016;PINHEIRO et al 2016). Most studies indicate the surface reservoirs as the main water container within a watershed (DE ARAUJO et al, 2004;MALVEIRA et al, 2012).…”

“…As regards arid and semi-arid ecosystems, soil water is of utmost importance to biogeochemical cycles and recycling nutrients (WANG 2012). In addition, it must be considered that the water strongly interacts with atmospheric processes, e.g., evapotranspiration, air temperature and rainfall (SENEVIRATNE et al 2010;PINHEIRO et al 2016).…”