page 3 (MCM) per year, and Sudan just 4 MCM. Thirty years later, renegotiation produced the 1959 Nile Treaty, in which Egypt was allocated 55.5 MCM per year, and Sudan 18.3 MCM. In turn, this agreement has recently been challenged by other riparian countries, who are interested in their own shares of Nile water (Whittington _et al.,_ 1994).

But political instability over water supplies, including possibly war, is always possible. Renegotiation of water-sharing agreements typically takes place in a tense atmosphere, sometimes exacerbated by threats and hostile actions. Two of the river basins in which riparians have recently objected to current water allocations--the Nile (Whittington _et al.,_ 1994) and the Jordan (Wolf, 1992)--lie in a politically volatile region--the Middle East.

Another aspect of water-sharing agreements that can lead to acrimony is enforcement. A state may have agreed to limit itself to a certain fixed volume of river water, but who or what is to stop it from increasing its consumption? Such unilateral violations of an agreement could take place openly or clandestinely. In fact, actual violations may be less damaging than the fear that other states are secretly engaging in routine violations.

In general, enforcement--comprising activities and structures designed to prevent or deter individual decisionmakers from acting in their immediate interests rather than complying with a specific regime--can be difficult and expensive. This is particularly true for environmental enforcement in an international context, where the prerequisites for domestic success, reliable information about behavior and credible threats of sanctions or penalties, are especially difficult to attain (Kilgour _et al.,_ 1992; Kilgour, 1994).

Fortunately, new technology will soon alleviate information problems for international agreements about the sharing of river water. Data on water levels gathered by satellite will be made available publically, permitting flow volumes and withdrawal rates to be calculated. (SADC, WB, and WMO, 1993) In addition, much more accurate forecasts of annual flow volumes will become available to all riparians.

Considerable political stability may be achieved simply through this sharp increase in the volume and accuracy of flow information. One likely consequence is much simpler and more effective enforcement. Furthermore, the availability of accurate one-year forecasts will play a fundamental role, permitting questions related to the stochastic nature of the flow to be sidestepped. There is no need to ensure that allocations are "on average" fair or welfaremaximizing if they can be modified annually so that they possess these properties every year.

Annual adjustment of allocations is certainly a new and promising idea. Studies by the UN Food and Agriculture Organization (1978, 1984) indicate that most water allocation agreements include static descriptions of both the supply of and the demand for water. For example, the 1959 Nile Agreement, predicated on the construction of the Aswan Dam, explicitly incorporates the assumption that "there will be an annual mean flow at Aswan of 84 MCM." Losses were estimated at 10 MCM, and the entire balance was confidently allocated to Egypt and Sudan with little or no explicit provision for years of below-normal flow.