The ecological security pattern plays a crucial role in maintaining ecosystem health and ensuring ecological security. The establishment of the ecological security pattern in Mudanjiang City can provide a scientific basis and effective support for stabilizing the ecological environment, mitigating regional human–land conflicts, and rational land- use planning. This paper utilizes the theory of constructing an ecological security pattern using a source-resistance plane-corridor node to grade the importance of source areas based on the connectivity index. It combines morphological spatial pattern analysis and PLUS model to generate and identify the present value of 2022 in Mudanjiang City, as well as predict eight land types and seven landscape types under three development scenarios by 2032. A transfer matrix and transfer-intensity map are introduced to explore the structural characteristics of landscape transfer, while four fragmentation indexes are combined with principal component analysis and the coefficient of variation method to form comprehensive fragmentation indexes for different classes. Finally, based on constructing the ecological security pattern of Mudanjiang City in 2022, an analysis method is developed that establishes logical connections between land-use structure, a comprehensive fragmentation of land types, landscape transformation mechanism, and the importance of ecological sources. The results are as follows: (1) In Mudanjiang City, 23 ecological source areas, 65 corridors, and 66 ecological nodes were extracted. The overall ecological security pattern shows a “U” shape with openings to the northeast. (2) The cumulative weight of economic and social factors on the ecological resistance surface in Mudanjiang City reached 51.36%. (3) The response between the comprehensive fragmentation degree of forest land and the importance of primary and tertiary source areas was highly significant, with R values reaching 0.9675 and −0.8746, respectively. The comparative study comprehensively showed that the best scenario for the sustainable development of the ecological security pattern in the future is an ecological priority scenario, where the tertiary source area with the smallest area proportion but strongest disturbance fluctuation becomes a key area affecting connectivity and overall ecological security pattern in Mudanjiang City.

Climate change has intensified extreme hydrological events in cold regions, threatening the stability of river ecosystems. The traditional monthly frequency method for calculating ecological flow assumes equal guarantee rates across all months, overlooking the complex nonlinear dependencies between interannual and intermonthly flows. This approach may result in flow values for certain months during low-flow years exceeding those of corresponding months in high-flow years, failing to align with actual hydrological patterns. This study integrates Copula functions with the monthly frequency method to establish an improved ecological flow calculation framework, accurately characterizing the statistical correlation between interannual and intermonthly flow variability. The Hailang River basin in Northeast China was selected as the study area. First, the SWAT model was employed to simulate natural runoff processes from 1956 to 1965. The calibration phase demonstrated excellent performance (R² = 0.84, NSE = 0.83), and the validation phase also met standards (R² = 0.82, NSE = 0.81). The improved method selected optimal Copula functions for each month through rigorous statistical tests (AIC, BIC, RMSE, and K-S test), establishing joint probability distributions for annual and monthly average flows. The results indicate that different Copula types better align with monthly hydrological seasonal characteristics: Gaussian Copula suits February, May, and July; t-Copula suits August; Clayton Copula from September to December; Gumbel Copula for January, March, April, and June. Through conditional probability relationships (P(X₀≥x₀, 90%) = 0.9), the monthly guarantee rate range determined by the improved method spans 81.83% to 90.08%, significantly outperforming the uniform 90% guarantee rate employed by traditional methods. Verification using the Tennant method confirmed that ecological flows throughout the year met “excellent” or higher standards. Ecological flows exhibited pronounced seasonal variation, ranging from 6.2 m³/s during winter to spring to 96.93 m³/s during summer to autumn, providing scientific basis for basin-scale ecological water management. This study establishes a reliable methodological framework for ecological flow management in cold-region rivers.