Abstract
Abstract. Accurate measurement of rainfall is vital to analyze the spatial and temporal
patterns of precipitation at various scales. However, the conventional rain
gauge observations in many parts of the world such as Ethiopia are sparse and
unevenly distributed. An alternative to traditional rain gauge observations
could be satellite-based rainfall estimates. Satellite rainfall estimates
could be used as a sole product (e.g., in areas with no (or poor) ground
observations) or through integrating with rain gauge measurements. In this
study, the potential of a newly available Climate Hazards Group Infrared
Precipitation with Stations (CHIRPS) rainfall product has been evaluated in
comparison to rain gauge data over the Upper Blue Nile basin in Ethiopia for
the period of 2000 to 2015. In addition, the Tropical Applications of Meteorology
using SATellite and ground-based observations (TAMSAT 3) and the African
Rainfall Climatology (ARC 2) products have been used as a benchmark and
compared with CHIRPS. From the overall analysis at dekadal (10 days) and monthly
temporal scale, CHIRPS exhibited better performance in comparison to
TAMSAT 3 and ARC 2 products. An evaluation based on categorical/volumetric
and continuous statistics indicated that CHIRPS has the greatest skills in
detecting rainfall events (POD = 0.99, 1.00) and measure of volumetric
rainfall (VHI = 1.00, 1.00), the highest correlation coefficients (r= 0.81, 0.88), better bias values (0.96, 0.96), and the lowest RMSE
(28.45 mm dekad−1, 59.03 mm month−1) than TAMSAT 3 and ARC 2 products at dekadal and
monthly analysis, respectively. CHIRPS overestimates the frequency of
rainfall occurrence (up to 31 % at dekadal scale), although the volume of
rainfall recorded during those events was very small. Indeed, TAMSAT 3 has
shown a comparable performance with that of the CHIRPS product, mainly with
regard to bias. The ARC 2 product was found to have the weakest performance
underestimating rain gauge observed rainfall by about 24 %. In addition,
the skill of CHIRPS is less affected by variation in elevation in comparison
to TAMSAT 3 and ARC 2 products. CHIRPS resulted in average biases of 1.11,
0.99, and 1.00 at lower (< 1000 m a.s.l.), medium (1000 to 2000 m a.s.l.), and higher elevation (> 2000 m a.s.l.), respectively.
Overall, the finding of this validation study shows the potentials of the CHIRPS
product to be used for various operational applications such as rainfall
pattern and variability study in the Upper Blue Nile basin in Ethiopia.