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Semi-arid regions are strongly dependent on the rainfall regime. Yet season identification is still ambiguous and clear definitions are lacking regarding which variables and criteria should be used. The objective of this work is to establish a method for hydrological season partitioning in the semi-arid Caatinga biome in northeastern Brazil considering precipitation, soil moisture and vegetation. The following four periods were employed for this purpose: (i) dry–rainy transition, (ii) rainy season, (iii) rainy–dry transition and (iv) dry season. The method was applied to the Aiuaba experimental basin (AEB) from 2003 to 2022. We observed a large inter-annual variability in the duration of seasons and a tendency for the rainy–dry transition season to increase, facts that may indicate changes in the hydrological regime of the region. This novel combination of precipitation, soil moisture, and vegetation data for identification of hydrological seasons within the Caatinga biome allows a detailed seasonal hydrological behaviour analysis. [ABSTRACT FROM AUTHOR]

Groundwater resources are the most reliable freshwater supply in arid regions where many aquifers face dramatic depletion due to natural and anthropogenic causes. The annual average rate of decline of groundwater level is about 1.65 m. This research focuses on an aquifer that suffers from severe groundwater stress, and it aims to identify the main causes of the stress and to understand the effects of climate change and human activity. Monthly data on groundwater level, precipitation, temperature, river discharge, evapotranspiration, soil moisture, and vegetation cover were collected from 2000 to 2020. The results indicate that declining groundwater levels mainly resulted from the expansion of vegetation cover rather than changes in hydro-climatic variables. Finally, this work highlights how significant financial investment in improving irrigation efficiency in the absence of socio-economic plans, education, awareness, and monitoring programmes unproductively resulted in the expansion of agricultural activities rather than preserving groundwater storage. [ABSTRACT FROM AUTHOR]

The association of hydrological models with remote sensing data allows the estimation of parameters that cannot be easily measured in situ, especially in regions with poor monitoring networks. In this paper, a distributed hydrological energy water balance model (FEST-EWB) was calibrated and validated in a basin located in a climate transition zone between a semi-arid region and the humid Atlantic Forest, in Brazil. Land surface temperature (LST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) were used to calibrate the model, that solves the system of energy and mass balance equations as a function of the representative equilibrium temperature. For validation, soil moisture and LST data collected in situ were used. The model presented good performance for the simulation of the variables studied in the basin, even with reduced availability of MODIS data due to cloud coverage, allowing the use of FEST-EWB in areas with these characteristics, which are common in many regions of the world. [ABSTRACT FROM AUTHOR]

Actual evapotranspiration/evaporation is essential in proper determination of potential recharge of semi-arid regions. Eight potential evapotranspiration methods with dual crop coefficient methodology were used to estimate actual evaporation (Ea) values from bare soil. Method comparison with measuredEavalues using lysimeter data for the hydrological years 2011/12 and 2012/13 identified better performance for the FAO-56-Penman-Monteith (NRMSE < 9%), Hargreaves-Samani (NRMSE < 13%), Priestley-Taylor (NRMSE < 15%) and Makkink (NRMSE < 14%) methods. Data of 2011/12, bestEaestimates and a water balance approach were used to calibrate six potential recharge models with linear, quadratic, exponential, cubic and power functions. Calibrated models were validated in simultaneous estimation of potential recharge and soil moisture using independent data for 2012/13. While models with linear/quadratic functions produced the weakest potential recharge estimates (ΔQ> 10%), the remaining models were acceptable. Soil moisture was acceptably simulated utilizing six models and four best evaporation methods (NRMSE < 20%). However, combination of the FAO-56-Penman-Monteith model with an exponential function produced the bestEavalues, soil moisture and potential recharge. [ABSTRACT FROM AUTHOR]

Estimating groundwater recharge is essential to ensure the sustainable use of groundwater resources, particularly in arid and semi-arid regions. Soil water balances have been frequently advocated as valuable tools to estimate groundwater recharge. This article compares the performance of three soil water balance models (Hydrobal, Visual Balan v2.0 and Thornthwaite) in the Ventós-Castellar aquifer, Spain. The models were used to simulate wet and dry years. Recharge estimates were transformed into water table fluctuations by means of a lumped groundwater model. These, in turn, were calibrated against piezometric data. Overall, the Hydrobal model shows the best fit between observed and calculated levels (r2 = 0.84), highlighting the role of soil moisture and vegetation in recharge processes. EditorD. Koutsoyiannis;Associate editorX. Chen CitationTouhami, I.,et al., 2014. Comparative performance of soil water balance models in computing semi-arid aquifer recharge.Hydrological Sciences Journal, 59 (1), 193–203. [ABSTRACT FROM AUTHOR]

Stable isotopes are powerful research tools in environmental sciences and their use in ecosystem research is increasing. Stable isotope measurements allow the study of evapotranspiration fluxes, soil evaporation and leaf transpiration phenomena. Soil water and leaf water are the sources of the evapotranspiration that transfers large quantities of water from land to the atmosphere; as a result the isotopic composition of water left in the leaves is modified towards enrichment. Evaporation also changes the isotopic composition of water bodies creating a natural isotopic signal. The isotopic identity of soil water affects the oxygen isotopic signature of leaf and stem water. In this paper we present the isotopic data of bulk leaf water, showing the enrichment in isotopic value of oxygen due to evapotranspiration from leaves in conjunction with the isotopic signal of rainwater and other environmental factors such as humidity and temperature. Results suggest that the variation in the values of δ18O of Eucalyptus citriodora, Dalbergia sissoo, Melia azedarach and Pinus roxburghii is due to the seasonal changes in the δ18O of the source water for plants, i. e. rain. It is further observed that leaf water δ18O values are depleted during the months of July, August and September. This occurs due to the following reasons: (a) the sampling areas receive about 50% of the average annual rain during these months, and (b) rainfalls during these months are isotopically depleted compared with winter rains. Citation Butt, S., Ali, M., Fazil, M. & Latif, Z. (2010) Seasonal variations in the isotopic composition of leaf and stem water from an arid region of Southeast Asia. Hydrol. Sci. J. 55(5), 844-848. [ABSTRACT FROM AUTHOR]