Risk assessment of water allocation on water scarcity period: the case of Jaguaribe-Metropolitan System

ABSTRACT The article evaluates the transfer of risk of a water allocation policy between two user sectors: urban supply and irrigation. The allocation between uses was performed using two methods: linear apportionment and assessment with priorities (adopted in periods of water scarcity). The amount available for allocation was obtained using two reservoir operation strategies: zero inflow in the second half of the year and forecast flow. Gains and losses of the user sectors were determined through benefits functions. The two allocation scenarios pointed to lower guarantees and benefits for user sector with less priority. The priority system revealed that the water transfer infrastructures provide gains for the higher priority sector when guaranteeing water security; however, cause losses when extinguishes the right to use the demand of lower priority, indicating that the allocation of water is also a distribution process risk. The transfer risk of this sector, volumetric and monetary, can be minimized with the use of climate information. Thus, an alternative to the allocation of water in environments with water transfer systems would be an acceptable risk in order to increase the current level of benefits of irrigation and the satisfaction of the urban supply. This risk can be established based on seasonal climate prediction models.

摘要 本文评估了城市供水（urban supply）与灌溉（irrigation）两大用户部门间水资源分配政策（water allocation policy）的风险转移问题。本次研究采用两种方法开展用水分配：线性分配法（linear apportionment）与优先级评估法（assessment with priorities，后者适用于水资源短缺（water scarcity）时段）。可分配水量通过两种水库调度策略（reservoir operation strategies）确定：下半年零入境径流情景与预报径流（forecast flow）情景。用户部门的损益通过效益函数（benefits functions）进行量化测算。两种分配情景（allocation scenarios）均表明，优先级较低的用户部门，其供水保障程度与收益均有所降低。优先级调度机制显示，在保障水安全（water security）的前提下，输水基础设施（water transfer infrastructures）可为高优先级部门带来收益；但当剥夺低优先级部门的用水需求使用权时，则会造成损失，这表明水资源分配同时也是一项风险分配过程。该部门在水量与货币层面的转移风险，可通过引入气候信息（climate information）得到有效缓解。因此，针对配备输水系统的水资源分配场景，为提升当前灌溉收益水平与城市供水满意度，可接受一定程度的可接受风险作为优化方案，该风险可基于季节气候预测模型（seasonal climate prediction models）进行量化设定。