Estimating Freshwater Discharge From The Greenland Ice Sheet With MODIS
Hudson, Benjamin 1 ; Overeem , Irina 2 ; Syvitski , James P.M. 3 ; Mikkelsen, Andreas 4
1 University of Colorado, Community Surface Dyamics Modeling System
2 University of Colorado, Community Surface Dyamics Modeling System
3 University of Colorado, Community Surface Dyamics Modeling System
4 University of Copenhagen
The Greenland Ice Sheet (GrIS) is the largest land bound ice mass in the northern hemisphere (Serreze and Barry, 2005). For the recent past (1992 to 2011) it is estimated the GrIS lost approximately 142 +/- 49 gigatons of mass (Shepherd et al., 2012) contributing 0.46 mm per year to sea level rise (Van den Broeke et al., 2009).
Despite its importance to global sea level, very few measurements of freshwater discharge from the GrIS exist. There are over 460 outlets of the GrIS of which 300 are land terminating river outlets (Lewis and Smith, 2009). Currently, only one river fed by the ice sheet has a published discharge record (Mernild & Hasholt, 2009). Two others were gauged as part of this work.
Given the lack of infrastructure in Greenland, efforts to gauge rivers via direct observations will likely remain ad hoc. Instead, remote sensing techniques must be developed to understand the discharge of liquid water from the GrIS and its role as a term in the surface mass balance of the GrIS.
We present work developing one such technique using the inundated area of a rivers braidplain as a proxy for river discharge. We used MODIS surface reflectance for pixels partially or entirely containing portions of the rivers braidplain.
We find that the technique shows promise, and that we can build an empirical relationship between MODIS surface reflectance for river pixels and discharge. We find that these relationships remain stable over at least five years (the longest record we have available). This also means that the technique is suitable for reconstructing river discharge histories back to the beginning of the MODIS record in the year 2000.
Despite the techniques promise, each river has its own relationship, and therefore in-situ information must be collected before the method can be applied to other rivers.
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Mernild, S.H., and Hasholt, B., 2009, Observed jokulhlaups and suspended sediment load from the Greenland ice sheet at Kangerlussuaq, West Greenland, 2007 and 2008: Journal of Glaciology, v. 55, no. 193, p. 855–858.
Serreze, M., and Barry, R., 2005, The Arctic climate System: Cambridge University Press.
Shepherd, A., et al., 2012, A Reconciled Estimate of Ice-Sheet Mass Balance: Science, v. 338, no. 6111, p. 1183–1189
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