A multi-source satellite data approach for modelling Lake Turkana water level: calibration and validation using satellite altimetry data

摘要

Lake Turkana is one of the largest desert lakes in the world and ischaracterized by high degrees of inter- and intra-annual fluctuations. Thehydrology and water balance of this lake have not been well understood dueto its remote location and unavailability of reliable ground truth datasets.Managing surface water resources is a great challenge in areas where in-situdata are either limited or unavailable. In this study, multi-sourcesatellite-driven data such as satellite-based rainfall estimates, modelledrunoff, evapotranspiration, and a digital elevation dataset were used tomodel Lake Turkana water levels from 1998 to 2009. Due to the unavailabilityof reliable lake level data, an approach is presented to calibrate andvalidate the water balance model of Lake Turkana using a composite lakelevel product of TOPEX/Poseidon, Jason-1, and ENVISAT satellite altimetrydata. Model validation results showed that the satellite-driven waterbalance model can satisfactorily capture the patterns and seasonalvariations of the Lake Turkana water level fluctuations with a Pearson'scorrelation coefficient of 0.90 and a Nash-Sutcliffe Coefficient ofEfficiency (NSCE) of 0.80 during the validation period (2004–2009). Modelerror estimates were within 10% of the natural variability of the lake.Our analysis indicated that fluctuations in Lake Turkana water levels aremainly driven by lake inflows and over-the-lake evaporation. Over-the-lakerainfall contributes only up to 30% of lake evaporative demand. Duringthe modelling time period, Lake Turkana showed seasonal variations of 1–2 m.The lake level fluctuated in the range up to 4 m between the years1998–2009. This study demonstrated the usefulness of satellite altimetrydata to calibrate and validate the satellite-driven hydrological model forLake Turkana without using any in-situ data. Furthermore, for Lake Turkana,we identified and outlined opportunities and challenges of using acalibrated satellite-driven water balance model for (i) quantitativeassessment of the impact of basin developmental activities on lake levelsand for (ii) forecasting lake level changes and their impact on fisheries.From this study, we suggest that globally available satellite altimetry dataprovide a unique opportunity for calibration and validation of hydrologicmodels in ungauged basins.