Due to climate change and human activities, the assumption of the stationarity of hydrological variables no longer hold, and increases the risk of water resources management. To analyze the risk of water allocation schemes under nonstationary conditions, a nonstationary stochastic simulation-based risk assessment method is proposed. This objective was achieved via the following five steps: probability distribution analysis, hydrological scenario setting, inflow stochastic simulation, allocation model optimization, and mathematical statistical analysis. This is the first time that the hydrological nonstationary has been considered in water allocation risk assessment. The methodology was applied to the Zhanghe Irrigation District to assess the risk of water allocation to the municipality, industry, hydropower, and agriculture. The Zhanghe reservoir annual inflow, which is the main hydrological variable in the district, was found to be nonstationary. The results showed that the risks of water allocation schemes are larger than 0.60, except for in the very low scenario. Moreover, through comparing with the results under the assumption of the stationarity, it is necessary to consider the nonstationarity of the Zhanghe reservoir annual inflow in the process of risk assessment.