A THREE-YEAR study has recently been carried out using a new technology (Dendrohydrology) at Laboratory of Dendrochronology and Plant Ecology of Pakistan Dept. of Botany Federal Urdu University of Arts, Science and Technology Karachi, Pakistan. This research was funded by Pak, US and Higher Education Commission of Pakistan and collaborated with Prof. Dr. Edward Cook from Lamont Doherty Earth Observatory Columbia University USA, Prof. Dr. Connie Wood House from Laboratory of Dendrochronology University of Arizona USA, Dr. Jonathan Palmer from Gondwana Tree ring Laboratory, New Zealand while from Pakistan Prof. Dr. Moinuddin Ahmed at FUUAST Ka
rachi, were the principal investigators of this project.
Water flow of Indus River at Partab Bridge for 500 years has been evaluated with the help of tree rings. As flow peaks in May-September time, therefore, five months were chosen for reconstruction. Average reconstructed flow is below the mean of gauge flow of Partab Bridge. Early period (1962-1987) of reconstructed flow is quite similar with the gauge data as compared to late period (1988-2000). It means that actual and reconstructed Partab flow is significantly correlated. High flow rate (mean= 3904 m3/s) was also observed during 1684-1700. Because results of actual and reconstructed mean flow have come closer to each other, we should use this reconstructed data for future prediction of River flow.
In this spirit, the long-term average reconstructed (3545 m3s-1) should be used as the best estimate of expected discharge from May to September at Partab Bridge in the future, but continued strong inter-decadal variability in the future, like in the past, would most likely to cause multi-departures from this expectation to occur. This statement assumes that climate change over the Upper Indus Basin (UIB) in the future do not affect the continuation of the interdecadal variabilty found. Past or significantly increase the melting of glaciers discharge component so far, it does not seem to be the case if the current stable state of Karakoram glaciers is an indication (Hewitt, 2005; Armstrong, 2010; Gardelle, 2012).
We found the most disturbing feature in the stream flow reconstruction during the prolonged period of 112 year low flow period from 1572 to 1683 where mean flow was 3377 m3/s which is 11% below the mean of gauge data. The driest period was 1637-1663 where mean reconstructed flow was 3271 m3/s and the flow was 8.1% below the average. This period, if repeat in the future will cause reduced Pakistans capacity for irrigation and hydroelectric power generation provided by Tarbela Dam which is the most worrying feature if happens in the future. Therefore we need more dams.
Finally, the May-September discharge reconstruction provides a signficant contribution to our understanding of the long-term streamflow dynamics of Upper Indus River, which is primarily controlled by meltwater contributions from seasonal snowfall and glaciers. It is a well-calibrated and validated reconstruction, both by comparison to the short instrumental record and back to 1452 when compared to independent tree-ring records of past hydroclimatic variability from the same UIB region.
The indicated presence of strong inter-decadal fluctuations in the reconstruction has emerged now as a common mode of hydroclimatic variability there, which could not have been deduced with any confidence from the short gaged record at Partab Bridge since 1962. This discovery further illustrates how short discharge records can severely limit our ability to statistically model hydrologic variability (Rodríguez-Iturbe, 1969). As such, the reconstruction helps fill the hydrological “data gap” for modeling the northern Pakistan part of the Hindu Kush-Karakoram-Himalayan region (Pellicciotti et al., 2012), and it should be useful to better plan for the future development of UIB water resources in an effort to close Pakistans “water gap” (World Bank, 2005).
Finally, the May-September discharge reconstruction provides the basis for comparing past, present, and future hydrologic changes, whichwill be crucial for detection and attributionof future hydroclimate change in the Upper Indus River Basin. At present, it appears that an observed persistant increase in UIB discharge from 1988 to 2008 is not statistically unprecedented and is more likely to be associated with increased meltwater from heavier prior winter snow accumulation than from enhanced summer glacier melting.
Bearing this in mind, the following conclusions are made
1. 550-year water flow data was obtained is the best long-term estimate
2. Hydroclimatic variability is not reliable on the basis of short term instrumental records
3. May-September flow reconstruction is a significantly contribution to understand the long term river flow dynamics of Upper Indus Basin
4. This flow is controlled by seasonal snow fall and glacier melt
5. This May-September reconstruction will provide the baseline for comparison of past, present and future hydrological changes
6. Increased flow from 1988-2008 (based on instrumental record) was due to previous heavy snowfall rather than summer glacier melting
7. Present study gave an additional support to the opinion that Upper Indus Basin glaciers are not retreating due to global warming