@MISC{Ward_3.water, author = {George H. Ward}, title = {3. Water Resources and Water Supply}, year = {} }
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Abstract
Of all of the elements of the Texas economy, society, and environment considered in this book, water is most closely coupled with climate. It is also the quintessential limiting factor for human development of the state. Simply put, “…the dominant feature of Texas is water, or rather, its scarcity ” (Fehrenbach, 1983). The present chapter focuses on availability of fresh water, i.e., water with sufficiently low dissolved solids that it can be used for human and animal consumption, for various agricultural and industrial enterprises, and for the wide suite of biological processes that require water of this quality. Specifically, this chapter addresses the question of whether there is a realistic potential for global warming, and associated climatological changes, to impact the availability of water in the state, and seeks an answer by a rudimentary accounting of the sources and uses of water and their responses to meteorological variables. Texas hydrology The ultimate source of fresh water in the state is precipitation, almost entirely rainfall. To understand the challenge of water management in the state, and to anticipate the effect that a greenhouse-warmed climate may have, it is necessary to trace the disposition of water after its delivery as rainfall onto the landscape of the state. This disposition is illustrated schematically in Figure 1. Rainfall impingent upon the surface immediately begins infiltrating into the soil. If the rainfall rate exceeds the infiltration rate, the excess ponds on the surface. Once this ponding suffices to establish continuity across the surface, the excess water can flow downslope. This downslope flow is runoff, and becomes organized into the network of drainageways incised into the landscape surface that collect and convey water, viz. streams and rivers. On a longer time period, some of the water infiltrated into the near-surface layer of the soil is evaporated, some is 1