Irrigation requirement estimation using MODIS vegetation indices and inverse biophysical modeling; A Case Study for Oran, Algeria
Marc
L..
Imhoff, NASA-GSFC, marc.l.imhoff@nasa.gov
(Presenting)
Lahouari
Bounoua, NASA-GSFC, lahouari..bounoua@nasa.gov
Shannon
S.
Franks, UMD, shannon.franks@nasa.gov
We explore an inverse modeling process using the Simple Biosphere model-SiB2 forced by satellite observed biophysical data and climatological data to quantify water demand in a semi-arid agricultural area by constraining the carbon and water cycles modeled under both equilibrium, balance between vegetation and prevailing local climate, and non-equilibrium, water added through irrigation, conditions. We postulate that the degree to which irrigated dry lands vary from equilibrium climate conditions is related to the amount of irrigation water used. The amount of water required over and above precipitation is considered as an irrigation requirement.
We added water using two distribution methods: The first method adds water on top of the canopy and simulates the traditional spray irrigation. The second method allows water to be applied directly into the soil layer and serves as proxy for drip irrigation.
Results show that for the month of July, spray irrigation resulted in an additional amount of water of about 1.4 mm per occurrence with an average frequency of occurrence of 24.6 hours. The simulated monthly irrigation for July was 34.85 mm. In contrast, the drip irrigation resulted in less frequent irrigation events, about every 48 hours, with an average water requirement amount of 0.6 mm per occurrence or about 43% of that simulated during the spray irrigation case. The simulated total monthly irrigation under this method for July is 8.8 mm; a remarkable 26.05 mm less than the spray irrigation method. When compared to a country-wide average estimate of irrigation water use, our numbers are quite low. According to our results, we would have to revise the reported country level estimates downward to 17% or less.
The numbers estimated from this work reflect an ideal physiologically-based target for efficient irrigation practices and could provide an objective basis for irrigation water use, especially in regions where water is already scarce
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