REGIONAL IMPACT OF URBAN WATER USE ON IRRIGATED AGRICULTURE

John G. Lee,. Ronald D. Lacewell, Teofilo Ozuna, Jr., and Lonnie L. JonesAbstract tively large rates of recharge and rapidLinear programming and regional input- groundwater movement. A market in wateroutput models were applied to estimate the rights has not evolved due largely to theimpacts of increased pumping costs for ir- fugitive nature of groundwater in theserigated agriculture due to groundwater deple- aquifers. This means market development fortion principally caused by the expanding ur- the Edwards and similar aquifers has been im-ban area of San Antonio, Texas. A biophysical peded, in part, due to the lack of exclusion.simulator was used to estimate linear pro- The lack of exclusion coupled with highgramming coefficients of crop yield by irriga- rates of recharge and groundwater movementtion level and timing. The results indicate can lead to an externality. Lin defines an ex-significant local (county) economic impacts ternality as a situation in which the privatefrom groundwater mining but insignificant economy lacks sufficient incentive to create aregional impacts. A major improvement in ir- market in some good and the nonexistence ofrigation efficiency would be required to offset this market results in losses in Pareto effici-the increased pumping costs and reduced ency. Randall indicates that the cost of exclu-water availability associated with increased sion for certain groundwater pools could be solifts due to urban expansion. large as to prohibit the establishment of trans-ferable groundwater rights. In addition,Key words: biophysical simulation, ground- Randall points out that some peculiarities inwater, regional input-output. the physical nature of the resource itself (e.g.,large rates of groundwater movement) canlead to high transaction costs which inhibitConsiderable research efforts have focused trade. Specifically, the transaction cost ofon the conversion of prime agricultural land to monitoring recharge and withdrawals may beurban uses (Ramsey and Corty; Burnham; prohibitive under the current institutionalSchmid). Less attention has been given to structure. A potential externality can exist inother natural resources for which urban and the case of the Edwards Aquifer because onerural users simultaneously compete. One such user can reduce the static groundwater level,resource is groundwater. Groundwater in thus reducing well yield and increasing liftTexas may be purchased either in conjunction and pumping cost for other users.with surface rights or as a separable right. Uvalde County, commonly referred to asUnder the predominant conjunctive rights the Winter Garden, provides a unique area insystem, the overlying land provides an ease- which to examine this potential externality.ment for extraction whereby ownership to in- This county overlays the Edwards Aquifer.dividual units of groundwater is assigned as Irrigated agriculture is a major sector of thethe water is removed. In an unconfined county's economy. Urban expansion in Sanaquifer, however, groundwater may resemble Antonio affects availability and cost of watera fugitive resource if it moves rapidly beneath to the agricultural users in Uvalde County.the land surface. The objectives of this study were to estimateThere are aquifers in Texas, such as the how projected future groundwater with-Edwards, which are characterized by rela- drawal rates of San Antonio will impact irri-