The review followed the PRISMA 2020 framework, screening records published between January 2021 and December 2025 in Scopus and Google Scholar. After removing duplicates and applying eligibility criteria focused on climate-driven hydrological change, flood hazards, snowmelt, and extreme precipitation, the team narrowed roughly 600 records down to 42 studies for final synthesis. Each study was then appraised across six dimensions: geographic relevance, hazard relevance, data quality, methodological rigor, future relevance, and decision relevance. This structured appraisal allowed the authors to distinguish conclusions supported by strong, consistent evidence from those requiring more cautious interpretation.

What emerges is a picture of a region already transformed. Central Asia has warmed by approximately 1.2 degrees Celsius over the past 70 years, and snow depth has declined by roughly 20 percent during the same period. Under the high-emission SSP5-8.5 scenario, warming could reach approximately 6.1 degrees Celsius by the end of the 21st century, implying substantial changes to snow storage, runoff formation, and flood-generating conditions across the region’s major river systems. Attribution analyses further indicate that anthropogenic forcing has already increased the likelihood and intensity of extreme temperature and precipitation events, particularly in mountain regions vulnerable to landslides, floods, and glacier-related hydrological change.

Extreme precipitation stands out as one of the most consistently reported and quantitatively supported drivers of flood-related hazards. Observational analyses covering 1936 to 2005 show that annual precipitation from wet days increased by 9.78 millimeters per decade, while the annual maximum one-day precipitation rose by 0.45 millimeters per decade. The proportion of precipitation falling on very wet days also increased, signaling a shift toward heavier rainfall events. Under the RCP4.5 scenario, projections indicate that total wet-day precipitation and maximum one-day precipitation would increase by 4.95 and 5.79 percent per degree of warming, respectively, implying thermodynamically strengthened rainfall extremes under continued warming.

Attribution evidence from vulnerable upstream regions of Kyrgyzstan and Tajikistan is particularly striking. Anthropogenic forcing has increased the frequency of extreme precipitation events by around 20 percent and their intensity by more than 100 percent in these mountain headwaters. Event-based analyses show that high-altitude parts of Central Asia experienced up to 698 extreme precipitation events between 1979 and 2023. These findings suggest that precipitation intensification is not uniform across the region but is becoming more spatially structured and process-dependent, with flood response varying considerably from one basin to another depending on elevation, catchment characteristics, and interactions with snow and glacier processes.

Snowmelt timing emerges as a second critical control on hydrological extremes. A large proportion of regional runoff is seasonally concentrated and influenced by snow accumulation, melt timing, and high-elevation hydro-climatic processes. In the Naryn basin, future warming is associated with a roughly 17 percent decline in maximum snow water equivalent, an advance of peak snow water equivalent timing by about one month, and runoff declines exceeding 40 percent in some upper-basin areas under high-emission scenarios. In the wider Tianshan-Pamir system, modeling suggests that by mid-century the frequency of rain-on-snow events will rise by approximately 49 percent, maximum daily intensity by roughly 43 to 45 percent, and annual total rain-on-snow intensity by approximately 66 percent, while the contribution of snowmelt to runoff may decrease by roughly 11 to 12 percentage points under SSP2-4.5 and SSP5-8.5 conditions.

Seasonal redistribution of runoff is perhaps the most consistent hydro-climatic feature reported across the reviewed literature. In the Sarykan River, summer runoff declined by 5.3 percent while runoff in the remaining months increased by 6.4 percent, indicating clear intra-annual redistribution. In western Kazakhstan, winter low flow increased by up to 5.2 times in parts of the Zhaiyk-Caspian system. Regional attribution analyses confirm that earlier spring streamflow peaks are widespread across Central Asian catchments. In the Kofarnihon River Basin of Tajikistan, climate change accounted for 87.96 percent of runoff change upstream, while anthropogenic activities accounted for 92.47 percent downstream, illustrating how the hydrological signal generated in mountain headwaters can be substantially modified as water moves through intensively managed lower reaches.

The review also highlights compound processes and interacting controls that defy simple attribution. The unprecedented flooding along the Tarim River in August 2022 was not generated uniformly across the basin: high temperatures and heat-related processes dominated some river systems, rainfall dominated others, and a combination of heat and rainfall affected still others. In the Amu Darya River Basin, long-term runoff reductions between 1960 and 2017 were mainly attributed to human activities including reservoir construction, cropland expansion, and irrigation demand, with the estimated contribution of human activities exceeding 100 percent at analyzed stations because anthropogenic effects counteracted an opposing climatic contribution. These findings underscore why future assessments must integrate climatic forcing with land-use change, urbanization, irrigation, and reservoir operation rather than treating them as separate categories.

Despite growing research attention, the evidence base remains geographically and thematically imbalanced. Region-wide Central Asian studies and Kazakhstan-specific analyses together account for more than half of the reviewed sample, while other single-country studies represent only 9.5 percent. Turkmenistan is particularly underrepresented, and conclusions for that setting should be regarded as especially cautious and provisional. Methodologically, observational trend and attribution analysis dominates at 54.8 percent of studies, followed by climate scenario modeling at 33.3 percent, while remote sensing, terrain-based hazard mapping, and dataset evaluation remain less developed. The literature is strongest in diagnosing hydro-climatic change but comparatively weaker in translating that understanding into operational flood risk tools, infrastructure criteria, or decision-ready adaptation frameworks.

The review identifies several priorities for future research: integrated multi-driver assessments that explicitly separate climatic and anthropogenic contributions; improved hydro-climatic observations and validation in mountain headwaters and transboundary basins; multidimensional flood characterization that accounts for frequency, duration, timing, and antecedent wetness; better integration of catchment and regulation effects including land-use change and urbanization; stronger country-specific and cross-basin synthesis; enhanced integration of transboundary systems into climate-risk research; and a decisive shift from hydro-climatic diagnosis toward adaptation-relevant risk assessment. Machine learning approaches, including sequence-based deep learning methods, could help capture non-linear dynamics among precipitation, snowpack evolution, temperature anomalies, and runoff timing in data-sparse basins. As Central Asia’s water authorities, river basin managers, and policymakers confront intensifying flood hazards alongside growing water stress, the review provides both a roadmap for future research and a structured evidence base for climate adaptation decisions across the region.

Subject of Research: Hydrological extremes and flood-related hazards in Central Asia under climate change

Article Title: Hydrological extremes and flood-related hazards across Central Asia: a systematic review and evidence-based synthesis of drivers, regional patterns, and research gaps

Article References: Sabitova, S., Broomandi, P., Bagheri, M., Arkhangelsky, E., Leuchner, M., & Kim, J. R. (2026). Hydrological extremes and flood-related hazards across Central Asia: a systematic review and evidence-based synthesis of drivers, regional patterns, and research gaps. Frontiers in Water, 8, Article 1890812. https://doi.org/10.3389/frwa.2026.1890812

Image Credits: AI Generated

DOI: 10.3389/frwa.2026.1890812

Keywords: Central Asia, flood hazards, hydrological extremes, snowmelt, rain-on-snow, extreme precipitation, climate change, runoff redistribution, transboundary basins, systematic review, water stress, climate adaptation