margarci@cicese.mx

https://orcid.org/0000-0003-3293-3000

Física Aplicada

zgonzale@cicese.mx

https://orcid.org/0000-0003-3293-0563

Departamento de Geología

The present study examines water resource management in the Guadalupe Basin, Baja California, a

elevation regions of the Sierra de Juárez exhibit higher precipitation, lower evapotranspiration, and

more favorable conditions for recharge, primarily due to infiltration through fractured bedrock and

forested soils. Conversely, the lowland valley areas experience persistent water deficits, high

evapotranspiration rates, and limited recharge, despite the presence of permeable alluvial sediments.

Vegetation has been shown to play a critical role in the regulation of infiltration and soil moisture

retention. The basin functions as a tripartite hydrological system, comprising recharge, transition, and

storage-limited zones. These findings underscore the vulnerability of groundwater resources to climate

change and anthropogenic pressure, underscoring the importance of safeguarding mountain recharge

areas to ensure long-term regional water sustainability.

El presente estudio examina la gestión de los recursos hídricos en la Cuenca Guadalupe, Baja California,

una región semiárida mediterránea caracterizada por una alta variabilidad climática, disponibilidad

limitada de agua superficial y una fuerte dependencia del agua subterránea. El objetivo principal del

estudio fue evaluar el balance hídrico climático y sus implicaciones para la recarga de agua subterránea.

Para ello, se utilizó un marco de Sistema de Información Geográfica (SIG), que incorporó variables

recarga limitada, a pesar de la presencia de sedimentos aluviales permeables. Se ha demostrado que la

vegetación desempeña un papel fundamental en la regulación de la infiltración y la retención de

humedad del suelo. La cuenca funciona como un sistema hidrológico tripartito, que comprende zonas

de recarga, transición y almacenamiento limitado. Estos hallazgos ponen de manifiesto la vulnerabilidad

de los recursos hídricos subterráneos al cambio climático y a la presión antropogénica, subrayando la

importancia de proteger las zonas de recarga de montaña para garantizar la sostenibilidad hídrica

regional a largo plazo.

Palabras clave: balance hídrico climático, método Thornthwaite-Mather, recarga de aguas subterráneas,

cuenca mediterránea semiárida, cuenca de Guadalupe

In the context of sustained global population growth and accelerating land-use transformation, pressure

on fragile ecosystems is expected to intensify substantially in the coming decades (Rockström et al.,

2009; Vörösmarty et al., 2010). These dynamics have exposed persistent deficiencies in land-use

planning and territorial organization, particularly in regions characterized by limited natural resource

availability (Wu et al., 2011; Bengtsson et al., 2006; He, 2018). One of the most significant

consequences of these deficiencies is the intensified exploitation of surface and groundwater resources,

especially to sustain irrigated agriculture and expanding urban systems. As a result, water availability

has declined markedly in many arid and semiarid regions, as evidenced by the reduction of ephemeral

streamflows, declining groundwater levels, and, in extreme cases, the abandonment of agricultural

activities. Water vulnerability has thus emerged as a central constraint affecting food production, energy

Orlowsky & Seneviratne, 2013; Trenberth, 2014; Jones et al., 2022). In semiarid environments, these

trends reduce the fraction of precipitation that effectively contributes to soil moisture storage and

groundwater recharge. Under such conditions, the accurate estimation of evapotranspiration becomes a

critical component of hydrological assessments, as evapotranspiration regulates the partitioning of

precipitation between atmospheric losses, surface runoff, and subsurface infiltration, thereby

influencing the balance between water supply and demand in water-limited basins (Droogers, 2000;

Lascano & Van Bavel, 2007).

Mediterranean-climate basins are particularly sensitive to these dynamics due to their pronounced

seasonality, strong hydrothermal gradients, and reliance on winter precipitation for groundwater

replenishment (Scanlon et al., 2006; Viviroli et al., 2020).

concentrated during short winter periods when precipitation coincides with low potential

evapotranspiration. Recharge is typically favored in high-elevation sectors where cooler temperatures,

reduced evaporative demand, and denser vegetation promote soil moisture retention and deep

percolation. In contrast, lowland areas frequently experience persistent climatic water deficits, even in

the presence of highly permeable alluvial sediments, because elevated temperatures and strong

evaporative demand rapidly deplete soil moisture. Understanding how climatic, geomorphological, and

ecological gradients interact to structure the spatial distribution of groundwater recharge is therefore

essential for anticipating future water availability under conditions of climate variability and land-use

change.

In semiarid regions, such as northwestern Mexico, groundwater is often the principal and only reliable

Within this context, the Guadalupe Basin, located in northwestern Baja California, Mexico, represents

a paradigmatic example of a Mediterranean semiarid watershed experiencing increasing water stress.

The basin exhibits pronounced topographic gradients, a marked east–west hydroclimatic asymmetry,

and heterogeneous land-use patterns dominated by agriculture, viticulture, and expanding urban

development. These characteristics make the basin particularly sensitive to changes in precipitation

regime, temperature, vegetation cover, and land management practices, all of which exert strong control

on evapotranspiration rates, runoff generation, and infiltration efficiency (Scanlon et al. 2002).

The present study applies the Thornthwaite–Mather climatic water-balance model in combination with

spatial and multi-criteria analysis to evaluate groundwater recharge potential across the Guadalupe

Basin.

potential evapotranspiration, and climatic water balance, together with geomorphological attributes

such as slope and elevation, vegetation patterns, and geological controls, within a Geographic

Information System (GIS). This integrative approach is particularly suitable for data-scarce semiarid

regions, where physically based hydrological models are often constrained by limited meteorological

and hydrogeological observations.

Accordingly, the central research question addressed in this study is how climatic, geomorphological,

and ecological controls interact to govern the spatial organization of groundwater recharge potential

under semiarid Mediterranean conditions (Wada et al. 2012; Valdes-Abellan et al. 2020). To address

this question, the study pursues three specific objectives: (i) to characterize the spatial variability of key

hydroclimatic drivers across the basin; (ii) to analyze the role of geomorphology and vegetation in

The Guadalupe Basin is located in the northwestern part of the State of Baja California, between

parallels 31° 51' and 32° 15' north latitude and meridians 115° 52' and 116° 51' west longitude (Beltrán,

2001). As illustrated in Figure 1, the relationship between the two variables is evident. The geographical

area under consideration encompasses an approximate area of 2,400 square kilometers, inclusive of the

estuary (Hernández-Rosas & Mejía-Vázquez, 2003). The area can be divided for the purposes of study

as follows: the north is divided by the Tecate-El Carrizo and Descanso-Los Medanos hydrological

basins; to the east, it is divided by the Laguna Salada hydrological basin; to the south, it is divided by

the Ensenada-El Gallo and San Carlos hydrological basins; and to the west, it is divided by the Pacific

Ocean (Campos Gaytán, 2008; Salgado et al., 2012; Figueroa-Núñez and Campos-Gaytán, 2018;

CONAGUA, 2014).

and Guadalupe valleys, and ultimately reaches the Pacific Ocean near the town of La Misión.

framework, giving rise to its hydrological processes. According to Regional Geological Mapping

(INEGI, 2006), four major lithological assemblages have been identified: intrusive igneous rocks,

extrusive volcanic sequences, metamorphic complexes, and unconsolidated Quaternary sediments.

Each of these units exhibits distinctive hydraulic characteristics that control groundwater input, storage,

and subsurface flow pathways across the basin (see Figure 2).

Intrusive igneous rocks represent the most extensive lithological group in the region. The crystalline

highlands that border the basin are composed of granodiorites, granites, diorites, and gabbros. Despite

the fact that these plutonic units possess a negligible degree of primary porosity, they are capable of

acquiring secondary permeability through the processes of jointing and fault-related fracturing. This

fracture network frequently serves as the primary mechanism that facilitates deep percolation during

fractured-bedrock aquifers within the Coast Ranges of California and in granitic terrains of central Chile

(Scanlon et al., 2002; Figueroa-Núñez & Campos-Gaytán, 2018). In this regard, the fractured igneous

uplands of the Guadalupe Basin function as both runoff-producing areas and localized recharge

domains, where the high density of fractures enables effective downward infiltration.

West of El Porvenir, extrusive volcanic rocks, primarily andesites, rhyolites and various volcanic tuffs,

are widespread and represent the remnants of Mesozoic volcanic activity associated with arc systems

in the region. The hydraulic behaviour of these rocks varies considerably. Massive or densely welded

tuffs form effective hydraulic barriers, whereas fractured or brecciated lava flows may allow more

efficient infiltration. As Houser et al. (2015) demonstrate, analogous heterogeneity has been

documented in the Trans-Mexican Volcanic Belt. In this region, contrasts in vesicularity, cooling

terrains compartmentalize aquifer systems and restrict basin-scale groundwater movement (Daesslé et

al., 2020).

The most hydrologically significant deposits, however, are the unconsolidated Quaternary sediments

that fill the Guadalupe Valley. Alluvial deposits are defined by their composition of gravels, sands, silts,

and interbedded sandstones. These deposits are distinguished by their high porosity and permeability.

These wetlands function as the primary groundwater reservoir for agricultural and domestic use, thereby

supporting ecological baseflows. Comparable valley-fill aquifers in other Mediterranean semiarid

regions, such as the Segura Basin in Spain and the Santa Ana Basin in California, perform similar roles

as key groundwater-storage and recharge systems (Valdes-Abellan et al., 2020; Scanlon et al., 2002).

Adding the 12 values of i.

consistency of the model. The climatic variables obtained included maximum, minimum, and average

temperature, relative humidity, wind speed, precipitation, extraterrestrial radiation, and sunshine hours.

The data were then organized, structured, and systematised in databases, following appropriate

calculation methods to determine reference evapotranspiration (ETo).

The processing of climate data was conducted using the QGIS Geographic Information System (GIS),

employing spatial analysis tools to generate thematic layers depicting temperature, radiation, sunshine

hours, and relative humidity. The calculation of ETo was achieved by establishing a relationship

between sunshine hours and other climate variables, in accordance with the method originally outlined

by Thornthwaite and Mather (1957). The model was fed with a 30-year series of climate records

for semiarid Mediterranean climates, showing consistency with reference ranges documented in

southern Spain, California, and central Chile (Guo et al., 2017; Valdes-Abellan et al., 2020). Secondly,

precipitation fields derived from gridded datasets were cross-checked with available station records

from CONAGUA and CICESE, confirming that spatially interpolated values fall within observed

seasonal ranges. Thirdly, the spatial patterns of climatic recharge potential correspond with the

previously reported fluctuations in groundwater levels within the Guadalupe Valley aquifer, particularly

in areas where mixing processes and deep percolation have been documented (Daesslé et al., 2020).

While it is recognized that these validation steps do not supplant direct hydrogeological measurements,

it is contended that they enhance confid ence in the internal coherence of model outputs and their

applicability under conditions where data is scarce.

Slope analysis was performed using a Digital Elevation Model (DEM). Slope was defined as the

maximum rate of change in altitude of each Digital Elevation Model (DEM) cell relative to its

neighboring cells. The methodology proposed by Van Zuidam (1986) was utilized for the classification

of slopes. Subsequently, the values obtained were adjusted to conform to geomorphological standards.

The classification resulting from this process is presented in Table 1.

The processing of geographical data in Geographic Information Systems (GIS) facilitated the generation

of slope maps and the identification of drainage patterns, thereby enabling the assessment of runoff in

the basin. In order to achieve this objective, a range of geospatial analysis techniques were employed,

including raster reclassification methods and spatial interpolation techniques. The advent of Geographic

Information System (GIS) tools has precipitated substantial advancements in the realm of data

presence of deep, coarse- to medium-textured soils has been observed to impede overland flow, prolong

residence time, and substantially enhance infiltration (see Figure 4A). These low-gradient sectors

function as natural infiltration corridors and represent the most favourable environments for focused

and diffuse recharge. Comparable recharge dynamics in low-relief alluvial plains have been

documented in semiarid Mediterranean basins of southern Spain, California, and central Chile, where

permeable sediments and gentle slopes promote infiltration even under strong seasonal water deficits

(Scanlon et al., 2002; Valdes-Abellan et al., 2020).

Conversely, the precipitous inclines (>20°) in the eastern and central regions adjacent to the Sierra de

Juárez facilitate expeditious runoff, impede infiltration due to the shallow nature of the soils, and

expedite the process of erosion. These steep sectors function as runoff-generation zones where

igneous and metamorphic rocks that are characterised by low permeability. This enhanced percolation

process is a significant factor in the contribution to deep groundwater accumulation (Daesslé et al.,

2020; Figueroa-Núñez & Campos-Gaytán, 2018).

These slope-controlled patterns are closely linked to the spatial distribution of vegetation cover (Figure

4B), since chaparral and forest-dominated slopes generally exhibit higher soil aggregation and moisture

retention, whereas degraded or agricultural surfaces on gentle slopes show reduced infiltration capacity.

It is imperative to incorporate vegetation into the interpretation of slope morphology to facilitate

comprehension of the spatial differentiation of runoff and recharge zones across the basin. The spatial

configuration of slopes establishes a hierarchical hydrological system within the basin, wherein steep

recharge environments. This morphometric organisation provides a foundation for the recharge patterns

derived from the water balance analysis and elucidates the concentration of infiltration potential in the

western and central basin sectors.

In the upper echelons of the Sierra de Juárez, the presence of oak-pine forest patches has been observed

to enhance soil-moisture retention. This phenomenon is attributed to the presence of thicker organic

layers, lower temperatures, and reduced PET levels in these regions. Consequently, the recharge

window is extended, resulting in a prolonged period of water accumulation. These forested zones

function as hydrological buffers that facilitate percolation into fractured bedrock, thereby strengthening

mountain-block recharge processes, as observed in other semiarid mountainous regions (Valdes-

Abellan et al., 2020; Houze, 2012). The riparian vegetation along the Guadalupe, Agua Caliente, and

especially in the western and central lowlands, have reduced infiltration capacity due to the removal of

vegetation, soil disturbance, and mechanized land management practices. The alterations have been

demonstrated to engender an augmentation in runoff coefficients, a diminution in soil water storage,

and an escalation in the basin's hydrological vulnerability (Salgado Tránsito et al., 2012). The spatial

overlap of these degraded areas with zones of high PET and negative climatic water balance (see Figures

4C-4D) further increases the susceptibility of these areas to moisture deficits and rapid runoff

generation.

Post-disturbance landscapes, including burned slopes and areas dominated by invasive grasslands, pose

significant hydrological challenges. The increasing frequency of wildfires in Mediterranean ecosystems

of Baja California has been shown to reduce canopy cover, increase soil hydrophobicity, and trigger

across mid-slope terrains.

Vegetation in the Guadalupe Basin forms a well-defined ecohydrological hierarchy. High-elevation

oak–pine forests function as primary recharge zones, while chaparral-covered slopes regulate soil

moisture dynamics and lateral flow redistribution. Riparian corridors maintain localized infiltration

pathways and enhance surface–groundwater connectivity (Smith et al., 2022). In contrast, agricultural

or degraded lowland areas exhibit reduced infiltration capacity and increased runoff generation. As

discussed in Sections 4.3–4.6, these vegetation–hydrology interactions are fundamental for interpreting

the climatic water balance and the spatial organization of groundwater recharge potential.

The hypothesis that temperature gradients reinforce this spatial behaviour has been demonstrated. The

has been observed to result in severe soil desiccation, amplified PET, and extremely low infiltration

efficiency, even during isolated storm events.

The distribution of precipitation, temperature, and seasonal hydroclimatic factors collectively delineates

a recharge landscape characterised by spatial asymmetries, including high-elevation recharge corridors

and lowland deficit zones. This imbalance underscores the imperative for the conservation of montane

recharge regions, the maintenance of vegetation cover across slope gradients, and the implementation

of land use practices that enhance infiltration and minimise soil compaction in mid- and low-elevation

areas.

Recent studies have demonstrated that vegetation cover has a significant impact on the spatial behaviour

of CWB. Forested regions and areas with mature chaparral vegetation have been observed to moderate

diminished infiltration capacity and elevated runoff coefficients. These modified landscapes have been

shown to have a substantial impact on local CWB values, often resulting in shifts towards more negative

balances. This phenomenon can be attributed to a decline in soil water storage accompanied by

increased evaporative losses (Salgado Tránsito et al., 2012).

It is evident that anthropogenic activities exert a substantial influence on shifts in CWB. The processes

of land clearing, soil compaction, road construction and vegetation removal disrupt natural infiltration

zones and redirect surface flow pathways. These disturbances have the effect of reducing the

hydrological buffering capacity of mid- and low-elevation zones, which historically served as recharge

corridors.

The spatial distribution of the CWB demonstrates the basin's structural vulnerability to water deficits

vegetation stress, and groundwater recharge efficiency in semiarid Mediterranean basins. In the

Guadalupe Basin, the spatial distribution of PET demonstrates a distinct west-east asymmetry in

hydrothermal conditions, which is directly associated with temperature, solar radiation, elevation, and

land cover patterns (Figure 4D). The western and central lowlands have the highest PET values,

reflecting warmer conditions, lower humidity, and extensive disturbed or agricultural soils. The

aforementioned factors have been demonstrated to engender an escalation in evaporative demand, a

acceleration in surface drying, and a reduction in the annual infiltration window (Eagleson, 2002).

Conversely, the elevated eastern sectors of the Sierra de Juárez demonstrate a significant decline in PET

levels, attributable to cooler temperatures, reduced solar exposure, and denser vegetation. The

prevailing hydroclimatic conditions have been demonstrated to engender prolonged soil moisture

precipitation (Figure 4E), and organic-rich soils in forested areas creates optimal conditions for

groundwater replenishment.

retention capacity makes them highly susceptible to evaporative losses under elevated temperature

texture or higher organic content – such as those found in forested uplands – demonstrate increased

moisture retention capacity. This capacity provides a buffering effect against the impact of PET. This

enhanced capacity is attributed to the stabilisation of soil-water storage throughout transitional seasons

(Gnann et al., 2022). These interactions serve to reinforce the spatial differentiation observed in the

climatic water balance (Figure 4C), where negative values predominate in regions with high PET.

The annual precipitation in the Guadalupe Basin exhibits pronounced spatial asymmetry, driven

primarily by orographic forcing, elevation gradients, and seasonal atmospheric circulation. Basin-wide

estimates indicate annual precipitation ranging from approximately 206 to 456 mm, with maximum

values concentrated in the eastern highlands of the Sierra de Juárez. Orographic uplift in this sector has

temperatures and reduced PET (see Figure 4D), these conditions significantly enhance soil moisture

retention, extend the recharge window, and promote both diffuse and focused infiltration in permeable

zones.

Conversely, the western and central lowlands receive less than 250 mm annually and exhibit persistent

climatic deficits (Jones et al., 2022, reinforcing their limited recharge capacity under high evaporative

demand. These hydrometeorological asymmetries, typified by uplands with high recharge and lowlands

with high discharge, are a hallmark feature of Mediterranean basins experiencing climatic water stress.

In these regions, valley floors and coastal plains are becoming increasingly vulnerable to warming and

drying trends (Valdés-Ábellan et al., 2020). Seasonality exerts a substantial influence on the basin's

hydrological regime, with over 85% of annual precipitation occurring during the winter months

evidenced by the findings that recharge is maximised when winter precipitation coincides with low PET

and increased soil saturation. During periods of drought, comparative analyses of semiarid watersheds

in California and northern Chile (Molina-Navarro et al., 2016) have demonstrated that the delayed

arrival or decreased intensity of winter storms substantially impacts annual recharge.

An integrated spatial analysis of slopes, vegetation cover, climatic water balance (CWB), potential

evapotranspiration (PET), precipitation, and temperature reveals the interconnected nature of the

Guadalupe Basin's hydrogeomorphology. Its hydrological functioning is collectively determined by

topography, climate, soils, and ecological patterns (Figures 4A–4F). The spatial alignment of these

variables reveals a persistent east-west hydroclimatic asymmetry characteristic of Mediterranean

retention, and prolong the period during which infiltration can occur. The fractured bedrock typical of

these areas further enhances vertical percolation, facilitating recharge processes consistent with those

observed in the mountains of Mediterranean regions in Spain, California, and Chile (Houze, 2012;

Valdés-Ábellan et al., 2020). This region clearly functions as the main recharge engine of the basin.

Mid-slope terrains serve as transitional ecohydrological zones where infiltration, runoff redistribution,

and soil-vegetation interactions occur. Slopes with a gradient of 7 to 20 percent are characterized by

dense chaparral vegetation that intercepts runoff and promotes partial infiltration. However, the

hydrological behavior of these slopes is highly sensitive to land disturbance. Vineyard expansion, road

construction, soil compaction, and vegetation clearing can rapidly shift these terrains from partially

infiltrating to runoff-dominated conditions. These threshold responses have been extensively