Localisation and temporal variability of groundwater discharge into the Dead Sea using thermal satellite data

U Mallast,R Merz,S Geyer,C Siebert,B Wagner,R Gloaguen,M Sauter

doi:10.1007/s12665-013-2371-6

Abstract

The semi-arid region of the Dead Sea heavily relies on groundwater resources. This dependence is exacerbated by both population growth and agricultural activities and demands a sustainable groundwater management. Yet, information on groundwater discharge as one main component for a sustainable management varies significantly in this area. Moreover, discharge locations, volume and temporal variability are still only partly known. A multi-temporal thermal satellite approach is applied to localise and semi-quantitatively assess groundwater discharge along the entire coastline. The authors use 100 Landsat ETM + band 6.2 data, spanning the years between 2000 and 2011. In the first instance, raw data are transformed to sea surface temperature (SST). To account for groundwater intermittency and to provide a seasonally independent data set ∆T (maximum SST range) per-pixel within biennial periods is calculated subsequently. Groundwater affected areas (GAA) are characterised by ∆T 10 °C. This allows the exact identification of 37 discharge locations (clusters) along the entire Dead Sea coast, which spatially correspond to available in situ discharge observations. Tracking the GAA extents as a direct indicator of groundwater discharge volume over time reveals (1) a temporal variability correspondence between GAA extents and recharge amounts, (2) the reported rigid ratios of discharge volumes between different spring areas not to be valid for all years considering the total discharge, (3) a certain variability in discharge locations as a consequence of the Dead Sea level drop, and finally (4) the assumed flushing effect of old Dead Sea brines from the sedimentary body to have occurred at least during the two series of 2000–2001 and 2010–2011.

Highlights

The water level of the hypersaline Dead Sea (DS) has been decreasing significantly for several decades
Those discharge areas are indicated in a previous study during which Mallast et al (2011) derived groundwater flow-paths
As the surface-runoff was excluded during the pre-processing step, all thermal anomalies with low DT values are assumed to reflect groundwater affected areas (GAA)

Summary

Introduction

The water level of the hypersaline Dead Sea (DS) has been decreasing significantly for several decades. Main reasons relate to the high evapotranspiration rates and a decreased groundwater/surface water contribution (Salameh and ElNaser 1999). Increased anthropogenic water abstraction from groundwater, the main freshwater resource in the region (Feitelson 2005), followed by the Jordan River—the only perennial surface water contribution to the DS have led to the reduction in water level. Groundwater quantity is the most difficult to assess (Al-Weshah 2000; Grabe et al 2012; Schulz et al 2013), which has resulted in numerous and discrepant estimates of groundwater discharge into the DS (Table 1). The significant discrepancies in the estimates can be attributed to the differences in the approaches employed by Environ Earth Sci (2013) 69:587–603 Author Q.

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Conclusion