Small water bodies are the only sources of water for the nomadic pastoral communities in East Africa. Severe shortages of water in the region have made these water resources of great importance to them (Fig. 1). As these resources are depleted during times of drought, they can become the reason for conflicts amongst rival communities in the region or for pastoralists seeking water from other regions. Satellite-based data has significantly transformed the way we track and estimate hydrological processes such as precipitation and evapotranspiration. Remote sensing offers a great advantage for improving hydrological monitoring, particularly in remote places where conventional station-based weather networks are scarce.

The waterholes (most of which have average surface area less than a hectare) were identified using Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) images with a spatial resolution of 15 m. Shuttle Radar Topography Mission (SRTM) elevation data with spatial resolution of 90m was used to delineate the watersheds of these small waterholes. Rainfall from the Tropical Rainfall Measuring Mission (TRMM) satellite data, having a resolution of 0.25 x 0.25 grid is extracted for the delineated watersheds in the study region. National Oceanic and Atmospheric Administration's (NOAA) Global Data Assimilation System (GDAS) data were used to extract the climatic parameters needed to calculate reference evapotranspiration. A simple hydrologic water balance model was developed that utilizes TRMM rainfall and modeled ET and runoff data to estimate daily waterhole depth variations.

Although there are no independent datasets to validate the results, the hydrologic water balance model captured both the seasonal and inter-annual variations, depicting known drought and flood years. As part of this research, water depth gauges have been installed in several waterholes and actual depth information is being gathered to perform periodic model calibration and validation. The simple water balance modeling approach demonstrated the effectiveness of integrating dynamic coarse resolution datasets such as TRMM with high resolution static datasets such as ASTER and SRTM DEM (Digital Elevation Model) to monitor water resources for drought early warning applications in these remote regions.

The water monitoring system webpage offers users the ability to monitor and download waterhole depth information from the year 1998. In phase II, Forty one representative waterholes in the region are being operationally monitored (with a day lag) for variations in waterhole depths. The site provides the current status of depth variations for each waterhole on a daily basis, which would enable decision makers to provide timely guidance and advisory in the pastoral regions.

Click here for a downloadable pdf describing some of the advantages and limitations of this project.

Acknowledgements

This research activity is a collaborative work between USGS/EROS and Texas A&M University, funded by NASA with a project title: "Enhancing the Livestock Early Warning System (LEWS) with NASA Earth-Science data, GPS and RANET technologies (05-DEC05-S2-73). Award # NNA06CH75I.

Hydrologic modeling work is conducted with graduate students at Geographic Information Science Center of Excellence (GIScCE), South Dakota State University by Manohar Velpuri and Henok Alemu along with their advisor Gabriel Senay.

The website is developed and maintained by Texas AgriLife Research, Texas A&M University System.