Muddied waters: The climate of High Mountain Asia is becoming warmer and wetter. Li et al . present data showing that rivers originating in this region have experienced large increases in runoff and sediment fluxes over the past six decades, most dramatically since the mid-1990s. The authors project that sediment flux from those rivers could more than double by 2050 in the case of extreme climate change, with potentially serious impacts on the region’s hydropower capacity, food security, and environment. —HJS

Climate change affects cryosphere-fed rivers and alters seasonal sediment dynamics, affecting cyclical fluvial material supply and year-round water-food-energy provisions to downstream communities. Here, we demonstrate seasonal sediment-transport regime shifts from the 1960s to 2000s in four cryosphere-fed rivers characterized by glacial, nival, pluvial, and mixed regimes, respectively. Spring sees a shift toward pluvial-dominated sediment transport due to less snowmelt and more erosive rainfall. Summer is characterized by intensified glacier meltwater pulses and pluvial events that exceptionally increase sediment fluxes. Our study highlights that the increases in hydroclimatic extremes and cryosphere degradation lead to amplified variability in fluvial fluxes and higher summer sediment peaks, which can threaten downstream river infrastructure safety and ecosystems and worsen glacial/pluvial floods. We further offer a monthly-scale sediment-availability-transport model that can reproduce such regime shifts and thus help facilitate sustainable reservoir operation and river management in wider cryospheric regions under future climate and hydrological change.

Accelerated glacier‐snow‐permafrost erosion due to global warming amplifies the sediment availability in cold environments and affects the time‐varying suspended sediment concentration (SSC) and discharge (Q) relationship. Here, the sediment‐availability‐transport (SAT) model is proposed to simulate dynamic SSC‐Q relationships by integrating the sediment availability coupled by thermal processes, fluvial processes and long‐term storage exhaustion into a sediment rating curve (SSC = a × Q^b with a and b as fitting parameters). In the SAT‐model, increased sediment sources from glacier‐snow‐permafrost erosion are captured by changes in basin temperature, showing an exponential amplification of SSC when basin temperature increases. Enhanced fluvial erosion by the elevated water supply from rainfall and meltwater is captured by the factor of runoff surge, which results in a linear amplification of SSC. The SAT‐model is validated for the permafrost‐dominated Tuotuohe basin on Tibetan Plateau utilizing multi‐decadal daily SSC/Q in‐situ observations (1985–2017). Results show that sediment rating curves for Tuotuohe display significant inter‐annual variations. The higher parameter‐b in a warmer and wetter climate confirms the increased sediment availability due to the expanded erodible landscapes and gullying‐enhanced connectivity between channels and slopes. Through capturing such time‐varying sediment availability, the SAT‐model can robustly reproduce the long‐term evolution, seasonality, and various event‐scale hysteresis of SSC, including clockwise, counter‐clockwise, figure‐eight, counter‐figure‐eight, and more complex hysteresis loops. Overall, the SAT‐model can explain over 75% of long‐term SSC variance with stable performance under hydroclimate abrupt changes, outperforming the conventional and static sediment rating curve approach by 20%. The SAT‐model not only advances understanding of sediment transport mechanisms by integrating thermal‐ and fluvial‐erosion processes, but also provides a model framework to simulate and project future sediment loads in other cold basins.