Satellite based Assessment of Groundwater Depletion by the Invasive Tree Species- Prosopis juliflora in a Semi-Arid Region of Gujarat, India

Gando Bawal (Mad Tree) as it is called by the people of Kutch, Gujarat is the non-native species originally known as Prosopis juliflora which was introduced in this semi-arid region in the year 1960 for rehabilitation of sodic lands and to prevent the encroachment of Rann desert onto the Banni grassland. Studies by Pasha et al. 2014 have suggested that there was an increase of 42.9% of area under Prosopis cover in Kutch during 1977 to 2011. Due to its invasive nature it has spread over large areas and invaded the pastoral grasslands of Banni region of Kutch, Gujarat. There is an increase in frequency of droughts and the people of Banni are blaming Prosopis juliflora as the culprit. Prosopis juliflora has depleted the ground water sources by accessing it through its long roots. To evaluate this and to assess the rate of groundwater depletion in this region here we used terrestrial water storage-change observations from NASA's Gravity Recovery and Climate Experiment satellites (GRACE) and simulated soil-water variations from a data-integrating hydrological model to show that groundwater is being depleted. The data set was prepared by collecting the measured precipitation, remote sensing evaporation and ground water table from the period of 2002 to 2017. During this period, the other terrestrial water storage components i.e. soil moisture, surface waters and biomass did not contribute significantly to the observed decline in total water levels. The study provided valuable information in understanding the net groundwater depletion rate by the tree species. Although our observational record is brief, the available evidence suggests that the consumption of groundwater by the tree species Prosopis juliflora is the cause why the region is going through shortages of potable water, leading to extensive socio economic stresses.