Ninth International Conference on Permafrost ... - IARC Research

Impact of Frozen Ground Change on Streamflow Hydrology Over the LenaWatershed in Siberia: A Preliminary AnalysisDaqing Yang, Ipshita Majhi, Doug KaneWater and Environmental Research Center, University of Alaska FairbanksTingjun ZhangNational Snow and Ice Data Center, University of ColoradoPermafrost limits the amount of subsurface water storageand infiltration that can occur, leading to wet soils andponded surface waters, unusual for a region with such limitedprecipitation. Changes in climatic conditions significantlyaffect the thermal regimes of active layer and permafrost(Pavlov 1994, Kane 1997, Frauenfeld et al. 2004, Zhang et al.2005). Warming of high latitude regions results in an increaseof active layer and permafrost temperatures, a deeper activelayer and talik development, lateral thawing of permafrost indiscontinuous and sporadic permafrost regions, and finallynorthward movement of the permafrost boundaries (Serrezeet al. 2000, Woo 1986, Zhang et al. 2005).Studies show that near-surface permafrost temperature innorthern Russia has increased by 0.6–0.7°C during the period1970–1990 owing to higher air temperature and deepersnow cover over Siberia (Pavlov 1994). In some regions ofSiberia, permafrost temperature has warmed more than 2°C(Zhang et al. 2005, Pavlov 1996), active layer thickness hasincreased by up to 20 to 30 cm, and talik over permafrostmay have developed over the past several decades. It hasbeen predicted that, under a moderate climatic warmingscenario, changes in permafrost temperature and activelayer thickness will become more significant in the next fewdecades in the Russian Arctic and Subarctic (Pavlov 1996,Lawrence & Slater 2005, Saito et al. 2007).Changes in timing, duration, and thickness of seasonalfreeze and thaw, talik development, and permafrostconditions have a significant impact on surface runoffand ground hydrology. Changes in active layer thicknessdirectly affect groundwater storage and river dischargethrough partitioning surface runoff (Kane 1997). A deeperactive layer delays the freeze-up dates of the active layerand allows drainage to occur later in the winter. Analysisof soil moisture data in the upper (1 m) layer in the formerSoviet Union over recent decades reveals a long-termincreasing trend of soil moisture north of 50°N, mainlydue to precipitation increases of 10–30 mm every 10 years(Vinikov & Yeserkepova 1991). Observation records showthat the absolute amount of water content increases 10–30mm in the 1 m soil layer, and groundwater level rose by 50–100 cm in Siberia. This increased groundwater storage mayresult in underground water recharge to the river system, andconsequently, a significant increase of runoff in the wintermonths.Recent assessments of the large rivers in the Arctic(i.e., the Lena, Ob, and Yenisei—drainage areas between2,400,000 and 3,000,000 km 2 , and contributing more than45% of the total freshwater inflow to the Arctic Ocean)identify significant changes in streamflow seasonal cycle(Yang et al. 2002, 2004a,b, Ye et al. 2003). For example,since the mid-1930s, the Lena River summer runoff hasnot changed significantly, but winter runoff has increased25–80%. In the Yenisei River basin, summer runoff hasdecreased by 20–30%, and winter discharge has gone upby 35–110%. The Ob River has also experienced a winterrunoff increase of 30–40%, and summer runoff has risen inJuly by 10%. Base (low) flow increases have been reportedover Siberian regions and watersheds. This may indicatehydrologic response to climate and permafrost changes. Thelinkage between streamflow and permafrost changes is notwell understood.This study applies comprehensive statistical methodsto examine the linkage between frozen ground and riverstreamflow changes. Statistical analyses include thecombinations of multiple-correlation, stepwise regression,and linear correlation and regression techniques. Thesemethods have been applied to data of river streamflow,temperature, precipitation, soil moisture, and active layerdepth. This allows us to establish statistical relationshipsuseful for identifying important climatic and permafrostfactors to regional streamflow changes. Further, it helpsto quantify lengths of memory of different variables(temperature, precipitation, snow cover, etc.) and theirimpact on interannual variation of river discharge.More specifically, this study examines the relation amongground temperature, active layer depth and base flowchanges. The focus of the analysis is placed on the regions/basins with significant changes, such as the Aldan tributary inthe upper Lena basin, where ground temperatures and winterflows have increased significantly in the last 40–50 years.The results of this work are useful in assessing the impact ofpermafrost changes on long-term streamflow variations overlarge watersheds, and they improve our understanding of theprocesses and interactions among climate, permafrost, andhydrology systems in the arctic regions.ReferencesFrauenfeld, O., Zhang, T., Barry, R.G. & Gilichinsky, D.G.2004. Interdecadal changes in seasonal freeze andthaw depths in Russia. J. Geophys. Res. 109: D05101,doi:10.1029/2003JD004245.Kane, D.L. 1997. The impact of Arctic hydrologicperturbations on Arctic ecosystems induced byclimate change. In: W.C. Oechel (ed.), Global Changeand Arctic Terrestrial Ecosystems. Springer-VerlagEcological Studies 124, 63-81.355