Validation of Satellite Precipitation Estimates using High-Resolution Surface Rainfall Observations in West Africa Paul A. Kucera and Andrew J. Newman NCAR/RAL Workshop on the Evaluation of High Resolution Precipitation Products 3-5 December 2007 12/1/2018

Operational Summary for NAMMA Location: Western Senegal, Cape Verde Islands and adjacent ocean. Time Period: 21 August – 30 September 2006. A total of 20 precipitation events were observed during the experiment. A variety of instruments were deployed in Senegal to measure precipitation: NPOL 10 cm Polarimetric Doppler Radar A network of high resolution rain gauges (38) Two video disdrometers 12/1/2018

NPOL Radar NASA 10 cm (S-Band) Polarimetric Doppler Weather Radar. Deployed in Kawsara, Senegal (40 km SE of Dakar). Scanned with a 15 min temporal and 200 m spatial res to a max range of 150 km. 12/1/2018

Rain Gauge Network in Senegal Large Scale Network 18 gauge sites were deployed to provide areal and range dependent coverage for NPOL. Provide ground verification data for evaluation of satellite and radar rainfall estimates. Deployed in June 2005. 12/1/2018

Rain Gauge Network in Senegal Dense Scale Network 20 rain gauge sites were deployed to examine small-scale rainfall variability. Deployed in August 2006. Both networks continue to be deployed. 12/1/2018

Seasonal Rainfall Variation for 2006 12/1/2018

Precipitation Events Observed by NPOL Event 1: 24-25 Aug 2006 Event 2: 25 Aug 2006 Event 3: 26 Aug 2006 Event 4: 27-28 Aug 2006 Event 5: 29 Aug 2006 Event 6: 30-31 Aug 2006 Event 7: 01-02 Sep 2006 Event 8: 02 Sep 2006 Event 9: 03 Sep 2006 Event 10: 05-06 Sep 2006 Event 11: 07-08 Sep 2006 Event 12: 11 Sep 2006 Event 13: 13-14 Sep 2006 Event 14: 14-15 Sep 2006 Event 15: 19 Sep 2006 Event 16: 22 Sep 2006 Event 17: 26 Sep 2006 Event 18: 27 Sep 2006 Event 19: 28 Sep 2006 Event 20: 29 Sep 2006 12/1/2018

Time Series of Precipitation Area Observed by NPOL 12/1/2018

Radar Rainfall Products NPOL data were QC’ed to remove ground clutter, second trip, side lobes and other non-meteorological echo. A + 2 dB bias correction (based on TRMM PR comparison) along with a ZDR correction was applied to NPOL data Radar rainfall maps were created using NPOL reflectivity mapped to a 5 km horizontal grid at an altitude of 2 km. Rainfall maps had a temporal resolution of 15 min. Reflectivity data were converted to rainfall rates using a Z-R derived from co-located disdrometer data: Z = 148 R1.4 Polarimetric-based algorithm is currently being developed. 12/1/2018

Satellite-Rainfall Comparisons Radar rainfall estimates were averaged to the 0.25 x 0.25 deg grids and accumulated to 3 h resolution. Comparisons were made with the following algorithms: TRMM Multi-satellite Precipitation Analysis (TMPA) CPC Morphing technique (CMORPH) NRL-Blended (NRLB) Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) HydroEstimator (HE) (Was not analyzed because of problems with the product files) The high resolution products (0.10 deg x 1 h) were not analyzed in the present study, but is planned for future analysis. 12/1/2018

Results 12/1/2018

Time Series: RMSE Algorithms tended to perform slightly better over ocean. CMORPH had the lowest RMSE on average. 12/1/2018

Time Series: POD POD is low for the TMPA algorithm. There is little difference between ocean and land. 12/1/2018

Time Series: HSS The TMPA algorithm had the lowest HSS. All algorithms are very similar for ocean and land. 12/1/2018

Daily Rainfall Comparison 12/1/2018

Case Study: 14 September 2006 Large, organized squall line with trailing stratiform. 0000 UTC 0200 UTC 0400 UTC 0600 UTC 12/1/2018

Case Study: 14 September 2006 12/1/2018

Case Study: 03 September 2006 Isolated Convection Case 1000 UTC 12/1/2018

Case Study: 03 September 2006 12/1/2018

Statistical Analysis Summary NRLB TMPA CMORPH PERSIANN Corr: 0.41 0.19 0.47 0.44 Bias: 1.34 0.78 1.18 2.21 POD: 0.63 0.28 0.58 0.64 FAR: 0.23 0.15 0.17 0.21 Cond RMSE: 6.95 7.68 6.77 6.93 Equitable TS: 0.28 0.10 0.27 0.26 Hedike SS: 0.43 0.19 0.43 0.41 12/1/2018

Summary During the field phase of NAMMA, the observed precipitation was episodic. A disturbance passed over Senegal every 1-3 days, larger systems every 3-5 days. Events ranged from unorganized, isolated convective systems to long-lived, organized MCS’s. Stratification of statistics indicated that algorithms performed similarly over ocean and land except for a few cases. Results indicate that the CMORPH algorithm performed the best overall. However, the PERSIANN and NRLB performed very similar. The TRMM 3B42 algorithm had the lowest performance. The CMORPH algorithm had the lowest bias of 1.18 and PERSIANN had the largest bias with a value of 2.19. More investigation is needed to better understand the large differences seen in some of the events. 12/1/2018

Future Work Short-term: Long-term: Continue to develop and evaluate NPOL radar rainfall products. Validation of high(er) resolution precipitation products. Spatial validation analysis. Long-term: Regional validation analysis in West Africa. 12/1/2018

Spatial Validation Spatial validation techniques aim to: Account for uncertainties in timing and location Account for field spatial structure Provide information of the errors in physical terms Provide information that is: diagnostic meaningful to users 12/1/2018

Radar Network in West Africa Current Radars Burkina Faso Ouagadougou Bobo Dioulasso Mali Bamako Planned Radars 2 installations in Mali Upgrade in Senegal Drawback Limited rain gauge network for error estimation 12/1/2018

Thank You 12/1/2018