This study analyzes long-term changes in minimal streamflow in the Zhaiyk-Caspian Water Management Basin (WMB), Western Kazakhstan, under climate variability. Using extensive hydrometeorological datasets (monthly discharge and daily meteorological records) from 1940 to 2021, the research assesses trends in low-flow characteristics across 18 hydrological posts. The analysis distinguishes two climatic periods: climate stabilization (pre-1973) and climate change (1974–2021). The methodology integrates hydrological and statistical analyses, including minimal monthly discharges, low-flow durations, soil freezing depths, and thaw frequencies. Findings reveal a widespread increase in winter low flows—up to 5.2 times—due to reduced frost depths and more frequent thaw events, enhancing groundwater contributions. Conversely, summer-autumn flows declined in several rivers, with drying trends linked to rising air temperatures and precipitation deficits. This study offers a novel, regionally adapted methodology for characterizing minimal streamflow under climate change, providing critical insights for hydrological drought assessment and water resource planning in arid and semi-arid environments.

This study presents a scenario-based assessment of the future sensitivity of minimal low-water runoff to climate change in Western Kazakhstan. An ensemble of global climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), combined with dynamically downscaled projections for Central Asia, was applied to estimate minimal monthly runoff during the summer–autumn and winter low-water periods for the rivers of the Zhaiyk–Caspian water management basin. The analysis covers three future time horizons: 2040 (2031–2050), 2060 (2051–2070), and 2080 (2071–2090), under two greenhouse gas concentration scenarios: SSP3-7.0 (moderately high emissions) and SSP5-8.5 (high emissions). The results reveal a pronounced seasonal contrast in the projected hydrological response. During the winter low-water period, a steady increase in minimal runoff is projected for all rivers, with the most significant changes observed for the Or, Zhem, Temir, and Shagan rivers. This increase is primarily driven by higher winter precipitation, increased thaw frequency, and enhanced infiltration recharge. Conversely, despite modest increases in summer–autumn precipitation, minimal runoff during the summer–autumn low-water period is projected to decline significantly, particularly in the southern basins, due to elevated evapotranspiration rates and soil moisture deficits associated with rising air temperatures. These findings emphasize the importance of developing seasonally differentiated, climate-resilient water management strategies to mitigate low-flow risks and ensure water security under future climate conditions in arid and semi-arid regions.

Droughts represent a major threat to water security and agricultural sustainability in the arid regions of Central Asia. The Balkhash–Alakol water management basin is particularly vulnerable due to its complex runoff formation, dependence on surface water resources, and the transboundary nature of the Ile River, the main inflow to Lake Balkhash. This study analyzes hydrometeorological data for 1950–2023 using the Standardized Precipitation Evapotranspiration Index (SPEI), Streamflow Drought Index (SDI), and Surface Water Supply Index (SWSI). Satellite-based indicators, including the Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST), were used to derive the Vegetation Condition Index (VCI), Temperature Condition Index (TCI), and Vegetation Health Index (VHI) for 2002–2023. Results indicate a significant increase in drought frequency and duration since the 1990s, with SPEI values reaching −2.6 during extreme events. Satellite observations revealed widespread vegetation degradation, with drought-affected areas (VHI < 30) exceeding 60% of the basin in severe years. Strong correlations between meteorological and hydrological drought indices (r up to 0.9) highlight the importance of cumulative moisture deficits. The results indicate an increase in the region’s aridity and the manifestation of drought in climatic, hydrological, and ecosystem changes. The practical significance of this study lies in the potential to use these results to improve drought monitoring and early warning systems, assess water risks, and develop measures for adapting to climate change and making decisions regarding water resource management in the Balkash–Alakol water management basin.

There is a global increase in the frequency and intensity of extreme floods driven by climate change, enhanced hydrological variability, and transformations in seasonal moisture accumulation and runoff formation processes. In recent decades, shifts in the temporal and spatial characteristics of spring floods have led to more frequent exceedances of design water levels and increased damage to water management systems, infrastructure, and agriculture. Regions dominated by snow-fed rivers are particularly vulnerable, as imbalances between winter moisture accumulation and spring snowmelt create favorable conditions for extreme flooding. This study presents a comprehensive assessment of the factors controlling high spring floods using the Esil River basin as a case study. The analysis is based on long-term hydrometeorological observations combined with climate projections from the Coupled Model Intercomparison Projects Phase 6 ensemble. Key flood-forming drivers considered include autumn soil moisture conditions, soil freezing depth, snow accumulation, spring precipitation, and the synchronicity and intensity of snowmelt processes. To identify critical combinations of climatic and hydrological factors, statistical and factor analyses were applied to construct a matrix of factor interactions reflecting historical patterns of joint influence on extreme flood formation. The results indicate that the most hazardous floods occur when increased autumn soil moisture coincides with deep soil freezing, significant snow accumulation, and rapid spring warming accompanied by intense precipitation. Even under average snow storage conditions, the probability of extreme flooding remains high when soil waterlogging is present and heavy spring precipitation occurs, confirming the nonlinear and multivariate nature of spring flood generation. Based on the identified interaction patterns, a set of baseline flood scenarios was developed. Scenario analysis under the SSP3—7.0 climate pathway suggests an increase in spring air temperatures by 1.5—2.0 °C and precipitation by 10—15% by the mid-twenty-first century, leading to higher flood magnitude and frequency. The results highlight increasing climate variability and cyclical water availability, emphasizing the need to adapt water management systems, enhance early warning capabilities, and implement proactive flood risk mitigation measures in snow-fed river basins of northern and central Kazakhstan. Graphical Abstract The graphical abstract illustrates an integrated system for assessing and forecasting spring flood risks in the Esil River basin in conditions of increasing climate variability and growing extremes in hydrological processes. The approach presented is aimed at a comprehensive analysis of the factors contributing to flooding and is based on the combination of diverse data and methods, which improves the reliability of flood risk assessment and forecasting accuracy. The methodological basis of the study includes the use of long-term hydrometeorological observations, snow cover characteristics, temperature regimes during the cold and transitional seasons, data on atmospheric precipitation, as well as information on land use patterns and anthropogenic transformation of the basin territory. The abstract presents a comparison of historically recorded floods and modelled scenarios reflecting possible changes in the flood regime under different climatic conditions. The results obtained emphasise the multifactorial and nonlinear nature of extreme spring floods in basins dominated by snowmelt. The graphic abstract demonstrates the potential of modern monitoring, analysis and modelling methods for improving early warning systems, flood risk management and the development of climate change adaptation measures in river basins fed by meltwater.

Гидрологиялық тұрғыдан қарағанда, Жайық-Каспий су шаруашылығы алабы аз зерттелген аудандар катарына жатады. Зерттеу ауданы гидрологиялық бекеттердегі бақылаулардың қысқа мерзімділігі мен олардың аумақ бойынша біркелкі орналаспауымен сипатталады. Гидробекеттердің жартысында бақылау деректері 10 жылға дейін құраса, үштен бір бөлігінде 5 жылдан аспайды. Сонымен қатар, алапта зерттелмеген шағын өзендер мен зерттелген өзендердің салалары болып табылмайтын сайлар көптеп кездеседі. Бұл жағдайда, өзендер режимі туралы ақпарат тек екі-үш жылдық бақылаулар арқылы берілген немесе мүлдем болмағандықтан, аз зерттелген және зерттелмеген өзендердің ағынды нормасын есептеу - гидрологиялық есептеулер тәжірибесіндегі ең күрделі жұмыстардың бірі болып табылады. Жайық-Каспий алабының аз зерттелген және мүлдем зерттелмеген өзендерінің ағынды нормасын анықтау үшін мақалада ағынды модулінің су жинау ауданына байланысты аймақтық тәуелділігі M0=f(F) пайдаланылды. Нәтижесінде, су шаруашылығы алабының гидрологиялық біртекті аудандарын сипаттайтын сегіз аймақтық қисықтары тұрғызылды. Өзен ағынды ресурстарының аумақтық таралу заңдылықтарын зерттеу нәтижелері алаптың ағынды модулі картасын құрастыруға мүмкіндік берді. Ағынды картасының изосызықтары 0,1-3,0 л/с×км² аралығында жүргізілді. Жалпы, ағынды модулінің таралуы климаттық сипаттамалардың солтүстіктен оңтүстікке қарай аймақтық өзгеруіне сәйкес келеді, сонымен қатар жергілікті жер бедерінің ерекшеліктерін ескереді. Алынған нәтижелер бақылаулармен қамтылмаған өзендер үшін ағынды нормасын есептеуге, суды пайдалануды жоспарлауға, экологиялық стандарттарды әзірлеуге және өзгермелі климат жағдайында су шаруашылығы іс-шараларын жүргізуге негіз болады. Зерттеу нәтижелері жоғары практикалық маңыздылыққа ие және гидрологиялық есептеулерде, су объектілерін жобалауда және аймақтық су саясатын қалыптастыруда қолдануға ұсынылуы мүмкін.

This study investigates the transformation of river runoff and its sensitivity to changes in large-scale atmospheric circulation in the Zhaiyk–Caspian water management basin during the period of 1951–2023. The analysis is based on hydrometeorological observations data, the Vangengeim–Girs classification of macro-circulation patterns, and the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) indices. Correlation analysis, the Mann–Kendall test, Sen’s slope estimator, and the Pettitt test were applied to identify trends, structural shifts, and the spatial coherence of hydroclimatic changes. The results show that interannual variability in river runoff is characterized by a degree of spatial coherence, with correlation coefficients between annual streamflow records at most gauging stations reaching up to 0.95. It is demonstrated that the most pronounced changes in the hydrological regime occur during the cold season and are expressed in a statistically significant increase in winter runoff, while no significant long-term trend in annual runoff is observed. Structural shifts in winter runoff are predominantly associated with the late 1990s, whereas changes in the temperature regime are detected earlier and exhibit spatial coherence. The findings indicate that the contemporary transformation of river runoff is primarily driven by rising air temperatures and the associated intra-annual redistribution of flow.