En esta era marcada por el cambio climático, la desertificación y el estrés hídrico se precisan como soluciones alternativas de bajo costo y alta efectividad para proporcionar agua a las comunidades rurales de bajos ingresos, a fin de satisfacer sus necesidades agrícolas y domésticas en armonía con su realidad geográfica. La presente obra examina cómo las sociedades agrarias de la cultura Nasca enfrentaron estos desafíos en uno de los desiertos más áridos del mundo, así como en los andes del sur peruano, cerca de la ciudad de Cusco, en áreas de intensas lluvias, difícil geografía y escasas tierras de cultivo. Se desea conocer, específicamente, cómo se obtuvo, guardó y distribuyó el agua y qué importancia tuvo el uso del agua subterránea y la de manantiales; se desea saber, igualmente, el potencial del Perú en cuanto a aguas subterráneas. Se revisa la literatura especializada para responder estas interrogantes y conocer cómo se realizó la gestión del agua en estas sociedades agrarias. Se plantea también que estas técnicas pueden ser potenciadas con tecnología de punta para mejorar la gestión de los recursos hídricos, como parte del esfuerzo internacional para enfrentar el cambio climático. | In this era marked by climate change, desertification and water stress, low-cost and high-efficiency alternative solutions are required to provide low-income rural communities with water, in order to satisfy their agricultural and domestic needs in harmony with their geographic reality. This study examines how agrarian societies of the Nasca culture faced these challenges in one of the most arid deserts in the world, and in the Andes of southern Perú, near the city of Cusco, in areas with intense rains, difficult geography and scarce cultivation lands. The objective is to understand, specifically, how water was obtained, stored and distributed, and what importance the use of underground and spring water had; likewise, the aim is to understand Perú's potential in terms of underground waters. Specialized literature is reviewed to respond these questions and to explore how water management was carried out in these agrarian societies. It is also suggested that these techniques can be strengthened with cutting edge technology to improve the management of water resources, as part of the international effort to face climate change.

We studied morphological and growth responses to drought of two sub-populations of Bromus pictus from communities with soils with different water availability from the Patagonian steppe. After a process of acclimatization common to both sub-populations, individuals from both sub-populations were subjected to three levels of water availability during 44 days. Independently of the water availability treatment, the sub-population from the community of high soil water availability showed higher aboveground relative growth rate (RGR) and higher leaf size (area and weight) compared to the sub-population from the community of low soil water availability. These results prove the expected evolution of higher growth rates and leaf sizes in resource rich environments. The sub-population from the community with low water availability also showed a higher tillering rate and a more prostrate morph than the sub-population from the community with high water availability. A higher number of small tillers may be a useful strategy for a quick response to water inputs and for distribute the risk of drought-induced mortality. A more prostrate morph may also present advantages like reducing the area exposed to dry air. The results obtained showed that soil heterogeneity may promote genetic variation. We were unable to detect statistically significant interactions between population and water availability treatments. The genetic variation found between the populations may be useful to develop breeding programs of a native species and may also increase the evolutionary potential of a native species to adapt to environmental changes<br>Nosotros estudiamos respuestas morfológicas y de crecimiento a la sequía para dos subpoblaciones de Bromus pictus provenientes de comunidades con suelos de distinta disponibilidad de agua en la estepa patagónica. Luego de un proceso de aclimatización común a ambas subpoblaciones, individuos de cada subpoblación fueron sometidos a tres niveles de disponibilidad de agua durante 44 días. Independientemente del nivel de disponibilidad hídrica, la subpoblación proveniente de la comunidad con mayor agua disponible exhibió una mayor tasa de crecimiento relativa aérea (RGR) y mayor tamaño foliar (área y peso) comparado con la subpoblación proveniente de la comunidad con menor agua disponible. Estos resultados prueban la evolución esperada de mayores tasas de crecimiento y tamaños de hoja en aquellos ambientes ricos en recursos. La subpoblación proveniente de la comunidad con menor agua disponible también exhibió una mayor tasa de macollaje y un hábito de crecimiento más postrado que la subpoblación proveniente de la comunidad con mayor agua disponible. Un mayor número de macollos pequeños puede ser una estrategia útil para una rápida respuesta a los pulsos de agua y para distribuir el riesgo la muerte inducida por sequías. Un hábito de crecimiento más postrado puede también presentar ventajas tales como reducir el área expuesta al aire seco. Los resultados obtenidos demuestran que la heterogeneidad del suelo puede promover variación genética, aunque no permitieron detectar interacciones estadísticamente significativas entre los factores vinculados con las poblaciones y la disponibilidad de agua. La variación genética encontrada entre las poblaciones puede ser útil para desarrollar programas de mejoramiento e incrementar el potencial evolutivo de una especie nativa para adaptarse a cambios ambientales

Abstract: Land use change is one of the main factors of natural ecosystem degradation, affecting nitrogen and water transfer between patches and reducing their productivity. This paper describes how conversion of desert scrub to savanna in central Sonora (RCS) has affected nitrogen and water pools and availability in the soil. Five sampling patches were chosen for each habitat: under the canopy of Olneya tesota trees (NA) and in the intercanopy bare soil (NI) in the desert scrub. Similarly in the buffel grass savanna under the canopy of the same tree species (SA), in bare soil (SI) and under Buffel grass (SB). We analyzed total and available near-surface soil nitrogen and soil water content at different depths during three years (2010 to 2013). We estimated an annual loss of 12.5 kg N ha-1 due to transformation of the natural scrub ecosystem, where trees and shrubs that serve as fertility islands were dominant, to buffel grass savanna. Soil water content in the topsoil was higher in the bare soil than in other habitats, but habitats with vegetation cover had higher water content than bare soil at 150-200 cm soil depth. Our results suggest that the desert scrub to savanna transformation has led to temporal and spatial decline of soil nitrogen and water. This change has affected the nitrogen and water pools, as well as the soil physical properties, soil fertility and water pools leading to an impact on hydrological budget and function of the transformed ecosystem. | Resumen: El cambio de uso de suelo es uno de los principales factores de la degradación de los ecosistemas naturales, al modificar los procesos de transferencia de nitrógeno y agua reduciendo su productividad. En el presente trabajo, se describe cómo la transformación de matorrales desérticos a sabanas de zacate buffel en la región central de Sonora (RCS) afecta dichos almacenes de recursos del suelo. Para entenderlo, se seleccionaron parcelas en el matorral bajo el dosel de árboles de Olneya tesota (NA) y espacios abiertos sin cobertura vegetal aparente (NI), y en la sabana de buffel, bajo la misma especie de árbol (SA), inter-espacio (SI) y bajo el pasto Buffel (SB). Se analizó el nitrógeno total y las formas disponibles de este nutrimento en el suelo, así como contenido de agua en el suelo a diferentes profundidades durante cuatro años (2010 al 2013). Se encontró una pérdida anual de 12.5 kg N ha-1 debido a la transformación del ecosistema natural dominado por árboles y arbustos que generan islas de fertilidad e inter-espacios, a una sabana dominada por buffel e inter-espacios a sabana. La humedad del suelo indica que en la parte superficial del suelo, los espacios abiertos tienen más humedad, pero en la parte profunda de 150 a 200 cm la cubierta vegetal de los árboles y buffel almacenan más agua. Los resultados sugieren que el cambio de matorrales a sabanas de buffel ha disminuido los reservorios de nitrógeno y agua, e impactado las propiedades físicas del suelo, la fertilidad, y los reservorios hídricos del suelo. El estudio sugiere que los cambios espaciales y temporales en nitrógeno y agua en el suelo repercutirán de manera importante en el balance hidrológico y funcionamiento del ecosistema transformado.

Dryland inland freshwater lenses (IFLs) that have been topographically induced are represented using physically modeled laboratory simulations, to characterize the stages of IFL evolution (i.e. formation, migration, degradation) as a function of recharge rate. Arid regions with shallow brackish to saline groundwater possess IFLs. The position and geometry (i.e. thickness, length) of IFLs over varying temporal and spatial scales is poorly understood due to their transient nature. The physically modeled IFLs in this study formed from an initial recharge pulse, after which IFL geometry was measured over time as it flowed in the direction of simulated groundwater flow. The time required for an IFL to reach the maximum thickness exhibited a negative exponential correlation to recharge rate. At IFL formation, thickness and length were positively correlated, and the ratio of IFL thickness to length exhibited a positive exponential correlation to recharge rate. After IFL formation, the central position of the simulated IFLs migrated laterally in the direction of groundwater flow at a velocity less than the range of applied recharge rates and greater than the groundwater flow velocities. The time required for the IFL to reach a minimum thickness, or IFL degradation, exhibited a positive exponential correlation to recharge rate. The Dupuit-Ghyben-Herzberg solution used to model coastal freshwater lens thickness was tested against the physically modeled IFLs and deemed invalid. A correction factor and modified solution are provided to predict IFL thickness, providing motivation for future analytical and numerical studies on inland variable-density groundwater systems in arid regions globally.

Quantifying dryland groundwater recharge as a function of climate variability is becoming increasingly important in the face of a globally depleted resource, yet this remains a major challenge due to lack of adequate monitoring and the complexity of processes involved. A previously unpublished and unique dataset of high density and frequency rainfall measurements is presented, from the Fowlers Gap Arid Zone Research Station in western New South Wales (Australia). The dataset confirms extreme spatial and temporal variability in rainfall distribution which has been observed in other dryland areas and is generally explained by the dominance of individual storm cells. Contrary to previous observations, however, this dataset contains only a few localised storm cells despite the variability. The implications of spatiotemporal rainfall variability on the estimation of groundwater recharge is assessed and show that the most likely recharge mechanism is through indirect and localised, rather than direct, recharge. Examples of rainfall and stream gauge height illustrate runoff generation when a spatially averaged threshold of 15–25 mm (depending on the antecedent moisture conditions) is exceeded. Preliminary assessment of groundwater levels illustrates that the regional water table is much deeper than anticipated, especially considering the expected magnitude of indirect and localised recharge. A possible explanation is that pathways for indirect and localised recharge are inhibited by the large quantities of Aeolian dust observed at the site. Runoff readily occurs with water collecting in surface lakes which slowly dry and disappear. Assuming direct groundwater recharge under these conditions will significantly overestimate actual recharge.

In drylands, groundwater is often the sole source of freshwater for industrial, domestic and agricultural uses, while concurrently supporting ecosystems. Many dryland aquifers are becoming depleted due to over-pumping and a lack of natural recharge, resulting in loss of storage and future water supplies, water-level declines that reduce access to freshwater, water quality problems, and, in extreme cases, geologic hazards. Conservation is often proposed as a strategy for managing groundwater to reduce or reverse the depletion, although there is a need to better understand its potential effectiveness and benefits at the local scale. This study assesses the impact of water-conservation planning strategies on groundwater resources in the Wadi El Natrun (WEN) area of northern Egypt. WEN has been subjected to groundwater depletion and quality degradation since the 1990s, attributed to agricultural and industrial groundwater usage. Initiatives have been proposed to increase the sustainability of the groundwater resource in the study area, but they have yet to be evaluated. Simultaneously, there are also proposals to increase the extent of arable land and thus demand for freshwater. In this study, three water management scenarios are developed and assessed to the 2060s for their impact on groundwater resources using a hydrogeologic model. Results demonstrate that demand management implemented through an optimized irrigation and crop rotation strategy has the greatest potential to significantly reduce risk of groundwater depletion compared to the other two scenarios—“business as usual” and “30% water-use reduction”—that were evaluated.