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American University of Beirut (2021)

EVALUATION OF CHIRPS AND GPM-IMERG PRECIPITATION ESTIMATES AGAINST GROUND RAIN GAUGE OBSERVATIONS OVER LEBANON

Sleiman Haidar, Aleel

Titre : EVALUATION OF CHIRPS AND GPM-IMERG PRECIPITATION ESTIMATES AGAINST GROUND RAIN GAUGE OBSERVATIONS OVER LEBANON

Auteur : Sleiman Haidar, Aleel

Université de soutenance  : American University of Beirut

Grade : Master of Science (MS) 2021

Résumé partiel
The objective of this paper is to assess two satellite precipitation products, Climate Hazards Center’s Infrared Precipitation with Stations (CHIRPS) and the product of the Global Precipitation Mission ; the Integrated Multi-satellitE Retrievals for GPM (GPM IMERG v4) against ground rain gauges over Lebanon. A network of around 84 rain gauge stations distributed over the area was used after extensive data quality control. This evaluation focuses on annual precipitation from hydrologic year 2000-2001 till 2016-2017, and on a monthly basis from January 2000 till April 2018 since this period was the common data available from CHIRPS and Ground stations. As for the common period between Ground data and IMERG, it was from 2014 till 2017. On a yearly basis CHIRPS recorded better results than IMERG (R2CHIRPS= 0.353 whereas R2IMERG= 0.084). Monthly analysis showed good performance by both satellite products with general underestimation by IMERG and slight overestimation by CHIRPS during wet months. January is the rainiest month in Lebanon with an average monthly precipitation of 163 mm. Moreover, the effects of longitude, latitude, elevation and location (topography) on precipitation readings were examined. Longitude values were categorized into 3 classes whereas Latitudes were divided into four due to the longitudinal geographical borders of Lebanon and based on a precipitation map. Results revealed that annually CHIRPS performed better at “Long2” (from 35.5 to 36) and “Long3” (from 36 to 36.6) than “Long1” (from 35.1 to 35.5). Also it overestimated rainfall at “Long1” and “Long2” when Ground-observed rainfall was below 800 mm and underestimated it when it reached above 800 mm. IMERG did not record a specific trend. As for the effect of Latitude, CHIRPS and IMERG performed better over the South at “Lat 4” (from 34.3 to 34.7) with R2CHIRPS= 0.515, RECHIRPS= 22% and R2IMERG= 0.688, REIMERG= 13.3%. On a monthly basis, neither latitude nor longitude had a noteworthy effect on the bias between remotely sensed and ground-observed precipitation.

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Page publiée le 20 mai 2021