Hydrological responses to climate change conditioned by historic alterations of land-use and water-use

摘要

This paper quantifies and conditions expected hydrological responses in theAral Sea Drainage Basin (ASDB; occupying 1.3% of the earth's landsurface), Central Asia, to multi-model projections of climate change in theregion from 20 general circulation models (GCMs). The aim is to investigatehow uncertainties of future climate change interact with the effects ofhistoric human re-distributions of water for land irrigation to influencefuture water fluxes and water resources. So far, historic irrigation changeshave greatly amplified water losses by evapotranspiration (ET) in the ASDB,whereas 20th century climate change has not much affected theregional net water loss to the atmosphere. Results show that errors intemperature (T) and precipitation (P) from single GCMs have large influenceon projected change trends (for the period 2010–2039) of river runoff (R),even though the ASDB is spatially well resolved by current GCMs. Bycontrast, observed biases in GCM ensemble mean results have relatively smallinfluence on projected R change trends. Ensemble mean results show thatprojected future climate change will considerably increase the net waterloss to the atmosphere. Furthermore, the ET response strength to any futureT change will be further increased by maintained (or increased) irrigationpractices, which shows how climate change and water use change can interactin modifying ET (and R). With maintained irrigation practices, R is likelyto decrease to near-total depletion, with risk for cascading ecologicalregime shifts in aquatic ecosystems downstream of irrigated land areas.Without irrigation, the agricultural areas of the principal Syr Darya riverbasin could sustain a 50% higher T increase (of 2.3 °C instead of theprojected 1.5 °C until 2010–2039) before yielding the same consumptive ETincrease and associated R decrease as with the present irrigation practices.