Research in the Zarafshon River Basin shows how modest changes in annual runoff can mask substantial shifts in seasonal water availability, with implications for agriculture in Tajikistan and Uzbekistan.

Climate change could alter when water reaches irrigation districts and farms in Central Asia, even where the total amount flowing through rivers each year changes relatively little. A study published this month in the Journal of Hydrology projects earlier peak flows and reduced summer water availability in the transboundary Zarafshon River Basin.

Led by researchers from FutureWater, the research examines how changes in snow, glaciers and rainfall could reshape the basin’s hydrology through the end of the century. Across the scenarios assessed, annual runoff declines by less than 7%, as increases in rainfall-runoff and baseflow largely offset declining snow and glacier melt. However, the annual discharge peak shifts 22–38 days earlier. For irrigation-dependent communities, that distinction matters: water arriving earlier in the year may be less available during critical summer growing periods.

Annual totals conceal seasonal pressures

The researchers used the SPHY glacio-hydrological model, calibrated against river discharge, satellite observations of snow cover and glacier mass balance data. Improvements to the representation of snowmelt and its infiltration into the soil helped capture how some meltwater is stored and released later. For the historical period of 1991–2020, the model estimates that snowmelt supplied around 52% of basin-wide runoff. Baseflow contributed approximately 23%, rainfall-runoff 21% and glacier melt 3%.

Although glacier melt makes a relatively small contribution to annual runoff across the basin, it plays an important role in sustaining late-summer low flows. The findings highlight the importance of assessing water availability by season and location, alongside annual totals. For agriculture, the timing of supply relative to crop-water demand is central to understanding future irrigation pressures.

The research is also relevant to initiatives such as ADB’s Glaciers to Farms regional programme, which connects climate science with adaptation planning, resilient agriculture and regional cooperation. A practical implication is that investment assessments should consider changing seasonal flows and downstream water needs, alongside glacier loss.

Read the paper: Khanal et al. (2026), “Climate change induced hydrological regime shifts in the transboundary Zarafshon River Basin in Central Asia,” Journal of Hydrology, 681, 136676.

Related programme: Glaciers to Farms — ADB regional programme summary.