**1. Introduction**

66 Current Issues of Water Management

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All humans need basic things or products for their material and physical well-being: air, water, food, shelter and others, all over the World, but in arid zones the prevailing condition is water scarcity. Besides the huge necessity of water for human consumption, agriculture and livestock demand large volumes of water. But sustainability for these activities is a highly fragile and complicated concept, difficult to be reached. Biomass production of a cash crop grown under drought will be lower than that grown under optimal soil moisture conditions; therefore in practical terms, it is not possible to obtain immunity against the effects of drought. In arid and semiarid zones, the environmental and agricultural issues depend on the availability of water and on its use efficiency, which is affected by high temperatures and elevated evapotranspiration rates. As a production dedicated activity, agriculture has changed dramatically especially since the end of the World War II. Food and fiber productivity were improved due to new technologies, mechanization, increased chemical use, specialization and government policies that favored maximizing production. These changes allowed fewer farmers with reduced labor demands to produce the majority of the food and fiber. But in this framework, one of the highest costs is the water extraction.

The objectives of this paper are to present a review about a method to assess the environmental and social dimensions of water issues through sustainability indicators in arid and semiarid zones, and to discuss the challenges for sustainability in terrestrial and agricultural ecosystems in a Mexican arid zone.

Assessing Environmental and Social Dimensions of

m. Hardening of subsurface horizon, and n. High temperature on the soil surface.

l. Physical loss of soil,

Water Issues Through Sustainability Indicators in Arid and Semiarid Zones 69

In arid soils, dryness and salinity, and their interaction under mismanaged irrigation, are the main causes of soil degradation. Effluent irrigation results in increased soil sodicity, because of the medium-to-high salinity and sodium concentration (Balks et al., 1998).

Bare soils exposed to rainfall are subjected to physical and chemical processes that change the hydraulic properties of the soil near the surface (Arie and Resnick, 1996). When the soil is dry, a hard layer is formed in the soil surface that is often called "desert crust", commonly enriched with calcite or silica. Desert crust decreases the infiltration rate of soils, thereby increasing runoff and soil erosion, reducing the availability of water through the root zone, and impeding seedling and plant growth (Figure 1.A). Other kind of crusts are formed in agricultural plots, irrigated with saline waters (Figure 1.B). Understanding the formation and properties of such crusts, as well as developing engineering methods to break it, are essential to control the runoff-infiltration (groundwater recharge) ratio and to maintain successful and sustainable agricultural activities. When desert crusts are a result of microbial activity, these kinds of crusts could help to protect the soil surface (Campbell et al., 2009). Besides, arid soils typically possess within a predominant sandy soil, a very low organic matter content with a consequent low fertility. In this sense, crop productivity under dryland conditions is largely limited by soil water availability. Soil organic matter (SOM) contents have been found to be a reliable index of crop productivity in semiarid regions

because it positively affects soil water-holding capacity (Diaz-Zorita, et al., 1999).

(a) (b)

**2.2 Vegetation and livestock control** 

soil because of salt accumulation in Chametla Baja California Sur, México

Fig. 1. Soil salinity symptoms and consequences. A: Photograph of soil fines and saline crusts; Wyoming, USA (http://www.powderriverbasin.org/assets/). B: Degraded unfertile

Vegetation may be the most important control on water movement in arid soils. Because vegetation in arid regions is opportunistic, when the water application rate is increased, plant growth increases as it uses up the excess water. The opportunistic nature of desert vegetation is shown by a significantly higher concentration of vegetation in areas of increased water flow, such as in ephemeral streams and in fissured sediments or rock-beds.
