Verification of Satellite Derived Precipitation Estimates Over Complex Terrain: A Ground Truth Analysis for Nepal

Satellite precipitation estimates are essential to the way we perceive the amount of rain that fell over a specific area when no weather station or rain gauge data is available. The TRMM satellite precipitation estimates play a key role in flood analysis and water resource management issues across many regions of the world where rain gauge data is unavailable. The southern Asian country of Nepal has some of the most extreme terrain gradients in the world, and the Nepalese government has a dense rain gauge network, both of which prove extremely useful for verifying TRMM estimations over a wide range of elevations. TRMM satellite precipitation estimates were used in comparison to the dense rain gauge network across Nepal. The time period of interest is from January 1998 - December 2011 because of the availability of the weather station precipitation measurements from the Nepalese government. Comparisons were made between daily, 3-day, 5-day, 7-day, 9-day, 11-day, and 13-day running means in order to find the optimum time span for which TRMM was most accurate across Nepal as compared to the weather station data. The TRMM satellite gridded precipitation values were then compared on a grid-by-grid basis to identify grid cells that are least accurate. After identifying these grid cells other environmental factors were taken into consideration to attempt to explain the lack of accuracy. Some of these factors include elevation, land cover, and slope.