Instream ecological flow is an essential determinant of river health. Intra- and interannual distribution characteristics of runoff have been altered to different degrees by dam construction. Historical runoff series with alterations, as basic data for ecological flow calculation, provide minimal instream hydrological process information, which affects the credibility of calculation results. Considering the influence of the alterations in runoff series on ecological flow calculation, the Gini coefficient (GI) is introduced to study the evenness degrees of the intra-annual runoff distribution of four hydrological stations located in the Naolihe basin of the Sanjiang Plain. The hydrological alteration diagnosis system is used to examine the alteration points in the GI series of each hydrological station for selecting reasonable subsequences. Based on the selected subsequences, the ecological flow of each station is calculated using three hydrological methods, and the comprehensive ecological flow is calculated using weighted calculation results from the three hydrological methods. The study results show that ecological flow and natural flow have similar processes with two peaks occurring in the process in May and August, respectively. Also, dams decrease the ecological water requirement damage frequency in dry seasons, but overuse of water resources increases the ecological water requirement damage frequency in flood seasons.

Mosquitoes pose a significant threat to global health, impacting over 40% of the world’s population. Currently, a dearth of large-scale and long-term data on mosquito populations in China hinders related research and public health endeavors. In response, we meticulously compiled and analyzed existing studies to construct a comprehensive dataset illustrating the spatial variation of mosquito populations, density, and composition across mainland China. This dataset furnishes invaluable information to support further research on mosquitoes and mosquito-borne diseases on broader spatial and temporal scales. The primary aim of this research is to contribute to efforts aimed at controlling mosquito transmission and mosquito-borne diseases, ultimately enhancing human well-being.

In spring, rivers at middle and high latitudes in the Northern Hemisphere are prone to ice jams, which threaten the safety of hydraulic structures in rivers. Heilongjiang Province is located on the highest latitude in China, starting at 43°26′ N and reaching 53°33′ N. Rivers in Heilongjiang Province freeze in winter and break up in spring. Forecasting the break-up date of river ice accurately can provide an important reference for the command, dispatch, and decision-making of ice flood preventing and shipping. Based on the observed break-up date series of river ice from seven representative hydrological stations in Heilongjiang Province, the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) was used to decompose the observed break-up date series of river ice into several subsequences, and the long-short term memory neural network (LSTM) was used to forecast the subsequences decomposed by CEEDMAN. Then, the forecast results of each subsequence were summed to obtain the forecasting value for the break-up date of river ice proceeded by CEEMDAN-LSTM. Compared with the LSTM, the forecast accuracy of CEEMDAN-LSTM for the break-up date of river ice had been significantly improved, with the mean absolute error reduced from 0.80–6.40 to 0.75–3.40, the qualification rate increased from 60–100% to 80–100%, the root-mean-square difference reduced from 1.37–5.97 to 0.95–1.69, the correlation coefficient increased from 0.51–0.97 to 0.97–0.98, and the Taylor skill score increased from 0.87–0.99 to 0.99. CEEMDAN-LSTM performed well in forecasting the break-up date of river ice in the Heilongjiang Province, which can provide important information for command, dispatch, and decision-making of ice flood control.

This study aimed to determine the influence of time and precipitation as covariates on the flood frequency distribution in the Songhua River tributaries under the nonstationarity assumption and to investigate the possibility of nonstationary models’ application in river management scope demarcation work. Nonstationary flood frequency analysis (NS-FFA) was conducted in three typical basins of the Songhua River (in Northeastern China) based on the generalized additive models for location, scale, and shape (GAMLSS), and stationary flood frequency analysis was used as a comparison. Under the stationarity assumption, the Pearson type Ⅲ (P-Ⅲ) distribution is the main theoretical distribution for the flood extremum at hydrological stations, followed by a lognormal (LN) distribution. Under the nonstationarity assumption, when time is considered a covariate, the optimal theoretical distribution of the flood extremum is mainly LN (with 63.75%), followed by the Weibull distribution (with 18.75%). When precipitation is considered as a covariate, the optimal theoretical distribution of the flood extremum is mainly LN (with 57.5%). We attempted to apply several FFA methods to calculate the design frequency in this study, referring to the work requirements for river management scope demarcation in three typical basins, and came to the following conclusions. From the simulation results of the p = 10% flood at the export stations of typical basins, it can be seen that time-covariate NS-FFA obtained the best simulation results. Two cases of the simulation under the stationarity assumption are positive, which will lead to a high design scale. The time-covariate GAMLSS in NS-FFA has the advantages of higher calculation accuracy and simpler processes. To better balance construction costs and disaster protection requirements, NS-FFA can be used to determine the design scale of water conservation projects; additionally, it can be used to demarcate the scope of river management. The accuracy of GAMLSS for FFA is also influenced by the complexity of the terrain, with basins with relatively simple terrain having higher calculation accuracy.

Wetlands have powerful runoff regulation functions, which can effectively store and retain surface runoff. The runoff regulation function of wetlands is affected by wetland areas, which affect the capacity of flood control. To explore the law of the area change of the main wetlands of the Naolihe River Basin (MWNRB), the visual interpretation method was used to extract wetlands. To identify the reasons for area changes in the MWNRB, the maximum likelihood method, minimum distance method, and neural network method were used to classify land use types from remote sensing images; the M-K variation point test and Theil-Sen trend analysis were used to test the variation point and calculate the trend of precipitation and temperature series. To clarify the influence of wetland areas on runoff, the Gini coefficient and SRI of runoff were used to calculate runoff temporal inhomogeneity. The results showed that the area of the MWNRB obviously decreased, with 74.5 × 10⁶ m²/year from 1993 to 2008, and increased slowly from 2008 to 2015, with 27.7 × 10⁶ m²/year. From 1993 to 2008, 50.74% and 38.87% of wetlands were transformed into paddy fields and dry fields, respectively. From 2008 to 2015, 61.69% and 7.76% of wetlands were transformed from paddy fields and dry fields, respectively. The temperature of the MWNRB increased slowly by 0.04 °C/year from 1993 to 2008 and increased obviously by 0.16 °C/year from 2008 to 2015. The precipitation decreased by 5.6–8.1 mm/year and increased by 16.6–41.2 mm/year in 1993–2008 and 2008–2015, respectively. Compared with precipitation and temperature, land use change caused by human activities is the main cause of wetland area change. The area change of the MWNRB has a certain influence on the runoff regulation and storage capacity. The Gini coefficient and SRI index increased from 0.002/year (0.008) to 0.023/year from 1993 to 2008 and decreased from 0.046/year (0.045) to 0.161/year from 2008 to 2015, respectively.