Francisco José Del-Toro-Guerrero

Quantifying actual evapotranspiration (ETa) in semiarid Mediterranean‐climate shrublands is limited by meteorological data scarcity, thus restricting the calculation of vegetation coefficients ( Kc ). Here, we integrated micrometeorological data, soil moisture observations and satellite‐derived spectral indices (red–near‐infrared and red‐edge bands) to calculate leaf Area indices (LAIs) using three empirical models within the FAO‐56 framework, which were subsequently validated using measurements from an eddy covariance (EC) tower within a chaparral ecosystem in the Guadalupe Valley, Baja California, Mexico, from June 2015 to September 2016. The spectral indices captured phenological seasonality and showed strong associations with measured ETa ( ET _EC ) ( R = 0.751–0.795). A normalised difference red‐edge (NDRE) index, based on RapidEye red‐edge band (690–730 nm), achieved the highest predictive accuracy. The structural overestimation in FAO‐56 parameterisation was corrected via calibration of an ecosystem‐specific scaling factor for the basal crop coefficient ( β = 0.33, 95% CI: 0.238–0.425). The estimated ETa ( ET _K ) ranged from 0.01 to 0.90 mm day ⁻¹ , closely aligning with the ET _EC of 0.11 to 1.03 mm day ⁻¹ . Leave‐one‐out cross‐validation (LOOCV, n = 17) yielded a Nash–Sutcliffe efficiency (NSE) of 0.66 and a percent bias (PBIAS) of +6.45%. However, including soil evaporation ( Ke ) degraded model performance substantially (NSE < −14 for all index‐LAI combinations), indicating that a transpiration‐only formulation is more appropriate for this chaparral, consistent with its relatively closed canopy and limited bare‐soil fraction. Overall, integrating high‐resolution remote sensing, specifically NDRE, with climate and soil data enables a robust characterisation of water balances in seasonal dryland ecosystems.

Groundwater pollution is one of the main challenges in our society, especially in semi-arid Mediterranean regions. This issue becomes especially critical in predominantly agricultural areas that lack comprehensive knowledge about the characteristics and functioning of their aquifer system. Vulnerability to groundwater pollution is defined as the sensitivity of the aquifer to being adversely affected by an imposed pollution load. For the Guadalupe aquifer, various indicators including water level depth, level variation, aquifer properties, soil composition, topography, impact on the vadose zone, and hydraulic conductivity were evaluated to establish spatial vulnerability categories ranging from very low to very high. Two pollution vulnerability scenarios (wet and dry) were studied. The results were compared with the analysis of nitrate concentration and distribution (2001, 2020, and 2021) from samples collected in the field. In the Calafia area, which predominantly relies on viticulture, the primary recharge inputs were identified in areas with a high vulnerability to pollution. Surprisingly, these vulnerable areas exhibited lower nitrate concentrations. This scenario underscores the need for effective management measures to safeguard aquifers in agricultural regions.

Evaluating how meteorological drought affects areas covered by natural ecosystems is challenging due to the lack of ground-based climate data, historical records, and weather station observation with limited coverage. This research tests how the surface reflectance–derived indices (SRDI) may solve this problem by assessing the condition and vegetation dynamics. We use long–term, monthly surface reflectance data (26 hydrological years, 1992/93–2017/18) from Landsat 5 TM, 7 ETM+, and 8 OLI/TIRS satellites and calculated the following five SRDI: Normalized Difference Vegetation Index (NDVI), Land Surface Temperature (LST), Vegetation Health Index (VHI), Normalized Difference Water Index (NDWI), and Modified Soil Adjusted Vegetation Index (MSAVI). The SRDI allows us to detect, classify, and quantify the area affected by drought in the Guadalupe Valley Basin (GVB) via correlations with the Reconnaissance Drought Index (RDI) and the Standardized Precipitation Index (SPI) (weather station-based data). For particular SRDI–RDI and SRDI–SPI combinations, we find positive seasonal correlations during April–May (IS2) and for annual (AN) values (MSAVI IS2–RDI AN, R = 0.90; NDWI IS2–SPI AN, R = 0.89; VHI AN–RDI AN, R = 0.86). The drought–affected GVB area accounted for >87% during 2001/02, 2006/07, 2013/14, and 2017/18. MSAVI and NDWI are the best meteorological drought indicators in this region, and their application minimizes the dependence on the availability of climatic data series.

Vegetation greenness (normalized difference vegetation index, NDVI) showed significant temporal and spatial correlations with precipitation and topography-derived features within the context of slope aspect (South- (SFS) and North-facing slopes (NFS) and an intermountain valley (IMV)) in a semi-arid Mediterranean-climate watershed in northwestern Baja California, México. Rank correlation with annual precipitation (1986–2016) showed a strong positive relationship with wet season NDVI at SFS (Rs = 0.82), IMV (Rs = 0.79), and NFS (Rs = 0.65) but moderate relation and only on hillslopes in the dry season (SFS, Rs = 0.47; NFS, Rs = 0.39). Thus, the vegetation on the more xeric SFS sites was more responsive to intra-annual and inter-annual precipitation than on either IMV or NFS. The correlation of NDVI with six topography-derived environmental attributes (elevation, slope gradient, curvature, drainage density, topographic wetness index, solar radiation) was weak to moderate, varied in degree and significance between years with exceptionally high or low NDVI, and often differed in sign between SFS, NFS, and IMV. Results showed that precipitation controlled vegetation greenness, under the three aspect conditions, more closely than did the other topography-derived features, and the sparse deciduous vegetation of SFS showed stronger associations with precipitation than IMV or NFS. The measurement of these relationships should be continued and complemented by other studies to improve the overall model, because they are important to modeling ecohydrology and productivity, and may be of use for projecting and hindcasting vegetation dynamics.

In this research, we examined temporal variations in soil water content (θ), infiltration patterns, and potential recharge at three sites with different mountain block positions in a semiarid Mediterranean climate in Baja California, Mexico: two located on opposing aspects (south- (SFS) and north-facing slopes (NFS)) and one located in a flat valley. At each site, we measured daily θ between 0.1 and 1 m depths from May 2014 to September 2016 in four hydrological seasons: wet season (winter), dry season (summer) and two transition seasons. The temporal evolution of θ and soil water storage (SWS) shows a strong variability that is associated mainly with high precipitation (P) pulses and soil profile depth at hillslope sites. Results shows that during high-intensity P events sites with opposing aspects reveal an increase of θ at the soil–bedrock interface suggesting lateral subsurface fluxes, while vertical soil infiltration decreases noticeably, signifying the production of surface runoff. We found that the dry soil conditions are reset annually at hillslope sites, and water is not available until the next wet season. Potential recharge occurred only in the winter season with P events greater than 50 mm/month at the SFS site and greater than 120 mm/month at the NFS site, indicating that soil depth and lack of vegetation cover play a critical role in the transport water towards the soil–bedrock interface. We also calculate that, on average, around 9.5% (~34.5 mm) of the accumulated precipitation may contribute to the recharge of the aquifer at the hillslope sites. Information about θ in a mountain block is essential for describing the dynamics and movement of water into the thin soil profile and its relation to potential groundwater recharge.

This paper used Landsat-5 Thematic Mapper (TM) data from 2007 to 2011 to examine seasonal changes in the normalized difference vegetation index (NDVI) in north-facing and south-facing slopes of a small (approximately 1900 ha.) west-draining hydrographic basin in the Guadalupe Valley in northwest Mexico. The analysis was done for the wet and dry seasons of this mid-latitude (32°N) basin with a rugged geomorphology covered by mostly native vegetation (chaparral) with minor anthropogenic disturbance. We used ten Landsat-5 TM satellite images that were preprocessed to correct atmospheric effects, to further estimate radiance and reflectance before the NDVI computation was performed. A LiDAR derived digital terrain model was used to calculate the terrain slope and aspect to further select and classify north and south facing slopes. With the slopes classified, zonal statistics of the NDVI were computed estimating mean and standard deviation for both slope orientations. We found higher NDVI values in the north-facing than in the south-facing slopes, regardless of the season (wet and dry), and also higher vegetation index values during the wet season compared to the dry season. For the period analyzed, we distinguished the signal of extreme dry year during 2007.

En este estudio se llevó a cabo la evaluación de los períodos de sequía histórica que han afectado al Valle de Guadalupe en el Estado de Baja California, México, el cual pertenece a la subcuenca que lleva el mismo nombre. En esta región se llevan a cabo actividades agrícolas de gran importancia como el cultivo de olivo, hortalizas, hierbas de olor y uva de mesa, siendo la más representativa la producción de uva para la elaboración de vino. Por ser una zona semiárida el recurso hídrico superficial es limitado, por lo tanto, toda la demanda de agua la provee el Acuífero Guadalupe. Para cumplir con el objetivo de este estudio se utilizó el cálculo del índice de reconocimiento de sequía (IRS) para llevar a cabo la clasificación anual histórica, la severidad, la duración y la frecuencia de la sequía meteorológica. Se encontraron cuáles han sido los periodos más representativos que han afectado a la región (1999 - 2009) y se concluye que los resultados generados pueden relacionarse con el descenso en el volumen de recarga del acuífero.