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Abstract:The high mountains of Central and South Asia provide irrigation water for their adjacent lowlands. The Indus Irrigation Scheme depends on approximately 50% of its runoff originating from snowmelt and glacier melt from the eastern Hindukush, Karakorum and western Himalaya. The Atlas of Pakistan indicates that these mountains gain a total annual rainfall of between 200 and 500 mm, amounts that are generally derived from valley-based stations and not representative for elevated zones. High-altitude snowfall seems to be neglected and is obviously still rather unknown. Estimates derived from accumulation pits runoff above 4000 m range from 1000 mm to more than 3000 mm, depending on the site and time of investigation, as well as on the method applied.To assess the vertical spatio-temporal distribution of total annual precipitation, a combined approach is presented. This approach links in situ measurements of snow depth and water equivalent (10-year time series derived from automatic weather stations at elevations between 1500 and 4700 m a.s.l.), the spatial distribution and period of snow coverage (remotely sensed data and digital elevation models), and the runoff characteristics of streams originating from snow or snow/ice-covered watersheds (modified snowmelt runoff model, including intermediate snowfall and glacier runoff).Based on conservative assumptions, the vertically changing seasonal ratio between liquid and solid precipitation is calculated. Using a combined snow cover and ablation model, total annual amounts of precipitation are derived for different altitudinal zones. Amounts of modelled and measured runoff complement the investigation. Horizontal gradients along the Indus-Gilgit-Hunza transect indicate the varying dominance of seasonal precipitation regimes (monsoonal, Mediterranean and continental disturbances) south of Nanga Parbat, between Nanga Parbat and Batura Wall (DWest Karakorum rainfall regime: 1500-1800 mm year 1 at 5000 m) and areas north of Batura (DCentral Asian rainfall regime: ¾600 mm year 1 at 5000 m).

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More than 200 000 ring-width measurements from 384 trees were obtained for 20 individual sites ranging from the lower to upper local timber-lines in the Northwest Karakorum of Pakistan and the Southern Tien Shan of Kirghizia. Samples were obtained predominantly from juniper species (Juniperus) and were analysed to reconstruct regional climatic variation patterns in Western Central Asia since ad 618. Site distribution represents diverse ecological conditions (e.g., combinations of temperature and moisture stress) within the Karakorum and Tien Shan mountains, permitting both intra-montane and inter-montane comparisons of chronologies. Three different types of chronologies re ecting interannual-, decadal-and centennial-scale ringwidth variations were calculated: a statistic skeleton-plotting technique was used to identify ring-width pointer years (interannual); a 101-year kernel lter was used to identify decadal-scale variations; and, for a subset of long-lived trees, the mean ring-width of the entire single series was used to identify centennial trends. After extracting and calibrating each of these three distinct wavelengths in ring-width variation, the results were combined into a comprehensive reconstruction re ecting primarily temperature uctuations in Western Central Asia since ad 618. The nature and the temporally changing strength of the climatic signals of this reconstruction are discussed in detail. A maximum latewood density record of Pinus tienschanica from Central Tien Shan was used as a predictor series to calibrate and validate tree-ring-width variation. In so doing, we link our results to the circumpolar maximum latewood-density network (Briffa et al., 1998a;1998b;Schweingruber and Briffa, 1996).

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