Evaluation of Satellite Rainfall Estimates Over Ethiopian River Basins T

Home , Awash River, Dawa River

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Sciences Discussions Earth System Hydrology and erent topographical fea- ff 7670 7669 erent spatial (mean annual total and number of rainy days) ff This discussion paper is/has beenSystem under Sciences review for (HESS). the Please journal refer to Hydrology the and corresponding Earth final paper in HESS if available. conventional rain gaugesmakes are them sparse. suitable for water The resource management near-real-time applications, availability however, an of over the SREs tions, PERSIANN consistently underestimated while theTMPA performance 3B42RT of varied. CMORPH and 1 Introduction High resolution satellite-based rainfall estimatesof (SREs) rainfall provide data an for alternative hydrological source applications especially in developing countries, where and temporal (monthly) totals. Whenout compared the to six ground regions, basedwere rain and gauges found for through- to the be yearsCMORPH season of and interest, independent. TMPA the 3B42RTwhile The performance performing PERSIANN of results provided better the varied more three than for accurate SREs lower PERSIANN results elevations, in in with the the southeast, northwest. At higher eleva- Basins surround the Ethiopiantures, Highlands, which as produces well di assix spatial regions and were temporal taken rainfall fromdiction patterns. three Center widely Precipitation morphing used estimates method high forSensed resolution (CMORPH), the Information SREs: Precipitation Using the Estimation Neural Climate from Networksthe Pre- Remotely (PERSIANN) Tropical and Rainfall the Measuring(TMPA) real-time 3B42RT. Mission version All of (TRMM) three Multisatellitegradient, SREs Precipitation but show Analysis exhibit the di natural northwest-southeast precipitation The objective of thisbased rainfall study estimates was (SREs) across to six(Kiremt) evaluate river and basins the minor within accuracy Ethiopia (Belg) duringthe of rainy the Awash, seasons high major Baro for resolution Akobo, the Blue satellite- years Nile, 2003 Genale to Dawa, 2007. Rift Valley The and six Wabi regions, Shebele River Abstract Hydrol. Earth Syst. Sci.www.hydrol-earth-syst-sci-discuss.net/7/7669/2010/ Discuss., 7, 7669–7694, 2010 doi:10.5194/hessd-7-7669-2010 © Author(s) 2010. CC Attribution 3.0 License. Evaluation of satellite rainfall estimates over Ethiopian river basins T. G. Romilly and M. Gebremichael Civil & Environmental Engineering, University of Connecticut, Connecticut,Received: CT, USA 25 August 2010 – Accepted: 25Correspondence September to: 2010 T. G. – Romilly Published: ([email protected]) 5 OctoberPublished 2010 by Copernicus Publications on behalf of the European Geosciences Union. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ected by the topogra- ff cult to physically locate or ffi 7672 7671 ect that topography has on the performance of SREs in particular is evidenced ff This study aims to evaluate the accuracy of three widely used SREs evaluated in Ta- The summarized results of Table 1 bring to light the idea that evaluation studies of The e The results of these studies indicate that the SREs performance varies with sea- Given that satellite rainfall estimates are contaminated by sources such as temporal vergence of tectonic plates. Thiswhich prominent are feature produces found the on Ethiopian Highlands, either side of the Great Rift Valley; the highest elevation along in the SREs on elevation. 2 Study region and data 2.1 Study region The Great Rift Valley highlightsand the splits complex the topography center found of within the Ethiopia country (Fig. in 1) the northeast and southwest direction by the di- routinely maintain, making their distributiontiveness, sparse. and To random address errors, the inherent spatialcomparing in representa- the rain SREs gauge to data, rainan gauge the intercomparison data methodology on of consists long the of term spatialthe averages. and spatial This seasonal study pattern patterns will of of perform the the SREs, SREs a bias, comparison as of well as evaluate the dependence on the bias SREs must be regional. (2009), specific, must and take into as consideration indicated the by elevation in Hong additionble et to 1 across the al. Ethiopia specific (2007) (CMORPH, region. PERSIANNregions and and (river Hirpa TMPA 3B42RT), basins). focusing et on Theare smaller SREs not are without compared error.lenge to This for ground ground is based based especially rain rain true gauges gauges, is in that which mountainous they regions, are often where di the chal- the Awash River Basin ofestimation Ethiopia at and higher found elevation-dependent elevationevaluated trends, the for with performance CMORPH under- of andtion CMORPH region TMPA and 3B42RT. of PERSIANN-CCS Bitew the Ethiopia in etCMORPH Highlands by a al. and 32% small (2009) and found high that PERSIANN-CCS by both eleva- 49%. underestimated total rainfall; al. (2009) performed an evaluation of CMORPH, PERSIANN and TMPA 3B42RT within elevations and that precipitation in the lower elevation were overestimated. Hirpa et a severe overestimation over themer central and spring CONUS months. and Zeweldi mountainfound et there west al. to during (2008) be the evaluated a CMORPH sum- the positive over bias winter Oklahoma during months. and the summer months, but a negative biasby during several studies within Tableraphy 1. might have Hong on et the al.cidental performance (2007) (SMO) of in evaluated PERSIANN-CCS western the within Mexico impact thephy. and Their that Sierra found study Madre topog- that showed Oc- the that bias light was precipitation a events were underestimated in the high itation over the centralHowever, during CONUS the fall and and winterthe mountain months mountain west PERSIANN west underestimated during and precipitation TMPA in work the 3B42RT of overestimated. spring Gottschalck Tian et and et al.that summer. al. (2005) there (2007) by was furthered evaluating an the CMORPH underestimation over over the the CONUS northeast and during found the summer months, but (CMORPH), Precipitation Estimation from RemotelyNetworks Sensed (PERSIANN) Information and Using Tropical Neural RainfallPrecipitation Measuring Analysis Mission (TMPA) (TRMM) 3B42. Multisatellite son, region andal. elevation. (2005) evaluated the Fortinental performace of United instance, PERSIANN States within and (CONUS)sonal TMPA and the 3B42RT precipitation found over United patterns. the the States, performance Con- Their to study Gottschalck be found et influenced that by both sea- SREs overestimated precip- a false sense of security or a higher false alarmsampling, rate. instrument and algorithmto error assess (Gebremichael the etevaluations accuracy al., of of 2005), three these it widely is estimates. used important SREs: Table Climate 1 Prediction summarizes Center recent morphing studies method on or underestimation in the actual rainfall amount could lead to analysis results that give 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 2 . The river basin, lo- 2 . This river basin, which , Awulachew et al. (2007) 2 2 ) and the largest (202 697 km 2 ering precipitation totals. The Belg, ff 7674 7673 towards the border between Somalia and Ethiopia. ff river basin is the second largest river basin assessed in this study 2 The Genale Dawa and Wabiern Shebele Ethiopia, River rank Basin, as found the in thirdriver south largest and basins (171 south 042 in km east- this assessment. The two river basins have similar topography, the lowest elevations ofapproximately 160 41% m of and the 175 totaland m, approximately elevation respectively. 65% range of for The the the rain total Genale elevation gauges Dawa rangeThe cover River for Basin Wabi Rift Shebele. Valley Riversmallest Basin, river basin located inhas in numerous this the lakes, assessment has southern elevation atThe ranging region rain 52 from 739 gauges of approximately km available 455 Ethiopia, m forrange. to use is 4175 cover m. the approximately 25% of the total elevation 199 812 km and has elevation ranging fromcover approximately approximately 57% 480 of m the to total 4250 m; elevation range. the rain gauges with their highest elevationseastern (4375 m boundary and of 4240 the m,basin. Great respectively) The Rift found topography Valley along in gently the the decreases north moving to west the corner south of east each and river reaches The Awash River Basin, whichthe starts Great in Rift Valley the towards the highlands northeast.the of list Although Central this Ethiopia, in river follows basin drainagereported falls area fourth that on at the approximately 112 AwashThe 696 km range River of is elevation considered forelevation the the range. rain most gauges utilized covers approximately river 47% in ofThe Ethiopia. the Baro total Akobo River Basin is the second smallest river basin assessed by this elevation range. The Ethiopianriver Highlands basin, with are lower found lands on situated the to the easternThe west. Blue edge Nile of River Basin the is– found the within Ethiopian the most Highlands. mountainousBasin Awulachew region et as of al. the Ethiopia (2007) most important identifiedto the river land Blue basin in Nile area, Ethiopia, River total with a annual significant rainfall, contribution population and agricultural production. The paper with acated drainage in area western of Ethiopia, has3220 approximately m; an 76 the 203 elevation rain ranging km gauges from used approximately by 400 m this to study fall within the middle third of the total – – – – – The following is a short discussion focused on Table 2: Figure 1 shows the ground based rain gauges that were available for conducting rainfall during the Kiremtdry (Seleshi season et and al., is approximately 2004; defined Segele by October et through al., the 2008). end of The February. This Bega is the 2.2 Climate Ethiopia has three distinctapproximately seasons, defined by each March with to the di endfor of most May, is of considered the the minorthe river rainy Indian season basins, Ocean and (Seleshi is etthe generated al., end 2004). by of weather September, The is systems Kiremt,of considered approximately that the the defined originate Intertropical by major over June rainy Convergence to season. Zone The (ITCZ) seasonal is oscillation the predominant mechanism for the Dawa, Rift Valley and Wabi Shebeleat River Basins least were 10 chosen rain based gauges onof per topography, a seasonal river threshold precipitation of basin, and climate. andAwulachew Table provides 2 et six provides al., drainage unique 2007), area study the (from regions approximatethe in elevation elevation range range terms for for the the river rain basin, gauges as within well the as given river basin. highlands descends and levels o The most mountainous terrain ishighlighted found by to the the Blue Nile northwest River. of the Great Riftthis Valley study and along is with the six study regions. The Awash, Baro Akobo, Blue Nile, Genale these highlands is in excess of 4200 m. The topography on the southeast side of the 5 5 20 25 15 10 15 10 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erence ff pixel for comparison with ◦ by 0.25 ◦ 7676 7675 ) and temporal (3-hourly) resolution, but achieve ◦ by 0.25 ◦ erent means. The morphing method, developed by the Cli- ff erence of 63 m. The 16 rain gauges within the Awash River Basin cover ff It is acknowledged here that rain gauges are merely point measurements and it is Figure 1 shows that the location of the gauges provided varied spatial representation The temporal resolution of the provided rain gauge data was monthly and in assess- Genale Dawa and Wabi Shebele River Basins, found in the south east, receive the The Awash and Rift Valley River Basins fall in the middle, when ranking the mean Table 3 provides the mean annual precipitation for each of the river basins, along data, however, due todata at the a limited temporal space-time resolution resolution of and 3-h, the gaps in desire the to MW generate data need to be estimated. In satellite data. However,period, we by have averaging minimized the the spatial representative rain error gauge in2.4 the observations rain gauge over estimates. a Satellite data five-year The three high resolutiontion satellite at products the evaluated same in spatial thisthe (0.25 paper estimates estimate using precipita- mate di Prediction Center (CPC), estimates precipitation using only microwave (MW) desired to have aestimates. densely populated Although network several of inrepresent the order a river to large basins compare majority containtypically them of a only with the network one satellite elevation of range rain rain within gauge gauges the within that given a river given basin, 0.25 there is of) gauges within eachdata of rich the of river theriver basin basins. river that basins cover The an evaluatedbetween elevation with Blue range any 37 of Nile, given 2138 rain rain for m. gaugeelevation gauges The example, station di maximum scattered is within elevation throughout di this the river the most an basin elevation is of 192 m, 1 978River with m. Basin an cover average In an stark elevationrange. contrast, range of the only 11 850 rain m, gauges or only within 30% the of Baro the Akobo total elevation approach chosen was to assess thethe data random using errors a in five-year average, the(Hirpa, thereby data, minimizing et making al., a 2009). qualitative assessment of the results possible of the individual river basins. This is evident by comparing the distribution (and number then it, along with the corresponding satellite data, was excluded from the study. The 70% of the datato (69% fill and in 68%, the respectively) missing for data the points, Kiremt. and There if was monthly no data attempt for a specific year was missing Rain gauge data, provided118 by stations the throughout Ethiopian Ethiopia. Meteorologicalare More Agency, defined than was as 75% a available principle for of (ortaken the first by rain class) trained rain gauges observers” gauge, in (Dinku which any is et one one al., that basin 2008). has “observations ing the rain gauges with recordedthere data between were 2003 missing and months. 2007 it Moreto became than 2007 apparent that 70% Belg of for the the data 8 was basins available evaluated; during only the Genale 2003 Dawa and Awash had less than annual precipitation, with 585 mmthirds and of 650 the mm, precipitation respectively. tothe The the annual Kiremt Awash precipitation River delivers to Basin two- and the the Rift Belg Valley River delivers Basin. almost2.3 half of Rain gauge data annual precipitation to theBasin. Baro Akobo River Basin, and 75%lowest to precipitation the totals Blue of Niletioned the river River six basins, river these basinsBelg. two assessed. The receive Unlike Kiremt more the providesas than two Wabi the half Shebele aforemen- least of receives amount the their least of precipitation amount precipitation during during for the the Genale Bega. Dawa, where mean annual precipitation. with the seasonal contributionern delivered river by basins, the Baro1465 Akobo Belg mm and and and Blue the 1305 Nile, mm, Kiremt. receive respectively. the The highest The two precipitation Kiremt west- totals contributes at more than half of the season was excluded from the analysis because of the overall low contribution to the 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 592 mm 1578 mm = = erent spatial pattern com- ff 28%). The Wabi Shebele and ∼ man et al., 2007). ff 7678 7677 erent spatial pattern compared to the other SREs (cor- ff 65%) followed by Belg ( ∼ 706 mm from CMORPH, 437 mm from PERSIANN, 806 mm from 1370 mm from CMORPH, 911 mm from PERSIANN, 1630 mm from = = As indicated in Fig. 2d–f, the three SREs show the northwest-southeast gradi- northeast, receives also moderatefrom CMORPH, amount 439 of mm from rainfall PERSIANN,majority (mean 717 falling mm annual from in rainfall TMPA 3B42RT), KiremtGenale with ( the Dawa vast Riverfalling basins in receive the theexhibit Belg smallest similar season. rainfall shapes amounts, of Forrainfall estimates with seasonal all are the rainfall consistently the higher pattern, majority sixthan than PERSIANN. CMORPH, however, river which TMPA are basins 3B42RT consistently considered, monthly higher the three SREs from CMORPH, 1059 mmover from most PERSIANN, of the 1762Valley mm River months, from basin, with located TMPA Kiremtannual in 3B42RT) contributing southwest, spread rainfall half receives moderate ofTMPA amount the 3B42RT), of with total rainfall more rainfall. (mean evenly rain distributed falling The across the in Rify rest the of the Belg months. season The (March–May) Awash River and basin, the located in rest the Figure 3 presents basin-averagedbasin monthly considered mean in (2003–2007) thisvariations rainfall study, in for as their each derivedNile river from seasonal River SREs. basin, rainfall locatedannual patterns The in rainfall river and the basins total northwest,TMPA show rainfall 3B42RT), receives large large amounts. with amounts(June–September), the peaking of vast The in rainfall July majority Blue (mean andin (74% August. the The to west, Baro 78%) also Akobo River receives falling basin, large in located amounts the of Kiremt rainfall (mean season annual rainfall relation of 0.936). PERSIANNtainous gives northwest slightly region compared lower to number the of other rainy SREs. days3.2 in the moun- Seasonal rainfall patterns PERSIANN exhibits slightly di ent in thehibit number similar of spatial rainy pattern days in in the the number region. of rainy days TMPA (correlation 3B42RT of and 0.999), CMORPH while ex- ber of rainy daysthree for SREs Ethiopia, show according the to largeTMPA 3B42RT each natural northwest-southeast and SRE. rainfall CMORPH As gradient(correlation indicated exhibit in of similar in the 0.995), Fig. spatial region. while 2a–c, patternspared PERSIANN the of to exhibits mean slightly the annual di hibit other rainfall similar SREs spatial (correlationthe mean of mountainous values, northwest 0.912). whereas region compared PERSIANN TMPA to underestimates 3B42RT the other especially and SREs. in CMORPH ex- 3 Results and discussion 3.1 Spatial precipitation patterns Figure 2 shows the spatial patterns of annual mean (2003–2007) rainfall and num- Rainfall Measuring Mission (TRMM) MultisatelliteReal Precipitation Time Analysis (RT) (TMPA) product 3B42 TRMM produces precipitation Microwave Imager estimates by (TMI),real converting Special time data Sensor data from Microwave/Sensor from the biting (SSM/I) the System and Advanced the (AMSR-E) Microwave Scanning using3-hourly Radiometer precipitation the for estimates, Goddard the IR Profiling data EarthCalibration is Algorithm. is Or- used performed to using In fill the order TMI in sensor the to (Hu gaps provide left by the MW data. vectors for which timeal., 2004). weighted averages Precipitation Estimation ofNeural from the Networks Remotely MW Sensed (PERSIANN) Information datato was using estimate are developed Artificial rainfall generated by by (Joyce the usingwhen available, IR et ground University based data of data as to Arizona input update the to in ANNs artificial (Hsu 1997 neural et al., networks 1997). (ANNs), The and Tropical order to fill the gaps in the MW data, infrared (IR) data is used to generate motion 5 5 25 15 20 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | grid cells ◦ by 0.25 ◦ erent pattern (correlation ff erences in elevation (Blue Nile and ff 7680 7679 SRE grid cells that contain rain gauges, and calculated ◦ by 0.25 ◦ ) measuring the strength of the fitted lines. The dependence of R erent river basins and two rainy seasons. ff In general, at elevations exceeding 1500 m, PERSIANN tends to underestimate in Figure 5 displays the bias ratio of SREs as a function of elevation for the main rainy the performance of theTMPA 3B42RT SREs; in the for Blue example,form Nile PERSIANN River PERSIANN in basin, outperforms the but Genale CMORPH CMORPHresults Dawa and are and River obtained TMPA basin 3B42RT for for outper- the a Belg similar season elevation (see range. Fig. Similar 6). all river basins, whileal. CMORPH (2009) and came TMPA to 3B42RT aal. outperform similar (2009) PERSIANN. found conclusion Hirpa a for slight et the(bias overestimation Awash for River CMORPH of Basin (bias 1.13) of alone, 1.11)in and in and Dinku excess TMPA their 3B42RT et of assessment 1500 m. for a At region elevations of lower the than 1500 Ethiopia m, Highlands there that is was a large variation in dominated by complex topography,Awash), and the large Bias di ratiomore of accurate estimates SREs at decreases lower as elevations,estimate. while elevation At CMORPH higher increases. and elevations, TMPA PERSIANN 3B42RT PERSIANN underestimates over- TMPA rainfall 3B42RT gives while give CMORPH and more accuratecomplex topography estimates. (Rift Valley and In Baroa the Akobo pronounced River river impact basins) basins on elevation does dominate the not Bias with have ratio less of SREs. for di season (Kiremt), for each riverand basin. correlation Also ( shownthe are Bias the fitted ratio lines of with SREs their on slopes elevation depends on the river basin. In regions that are relationship between the Bias ratio at each grid cell and the elevation of the grid cell, indicates overestimation by SRE, aby bias SRE, ratio and less a than bias one ratio indicates of one underestimation indicates no bias in the SRE. Fourth, we examine the Here, we quantify the biasOur in the procedure SREs consists as of asonal function the mean of following rainfall elevation steps. in at the eachwe First, six rain extracted river we the gauge basins. 0.25 calculated station based thethe on five-year five-year the sea- seasonal rain mean gauge rainfalldata. data. at each Second, grid Third, cell based weratio on calculated statistic, the corresponding the which SRE bias iscorresponding seasonal defined in mean as the rainfall of the SREs rain seasonal gauge at data. mean each A rainfall bias grid of ratio cell greater SRE than through divided one the by Bias the the country. Similar to the otherthe SREs, northwest. PERSIANNs best performance is found towards 3.4 Dependence of bias ratio in SREs on elevation of 0.895 and 0.878, respectively). CMORPH,performs with better a in country averaged the bias northwestto ratio of portion underestimate 0.89, of in the the countrycountry (0.75 central averaged to and bias 1.25), southeast withdeviation ratio a (0.50 when closer tendency to compared to to 1.00).northwest the the (1.00 ground TMPA other to 3B42RT truth SREs. 1.25) has1.00). (1.05) and There a PERSIANN but a is exhibits slight a severe a underestimation, underestimationof higher slight with 0.57. towards overestimation standard a the The in country highest southeast the averaged degree (0.75 bias of ratio to underestimation is found throughout the central part of Figure 4 presents thethe spatial three pattern SREs with ofthat the the contain bias a mean rain ratio gauge. annual presented(correlation CMORPH bias for of and ratio each TMPA 0.978), 3B42RT while (2003–2007) of exhibit similar PERSIANN the for spatial exhibits 0.25 patterns a slightly di 3.3 Spatial pattern of bias ratio 5 5 15 20 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Business + Business Media + man, G., and Adler, R.: A detailed ff 7682 7681 erences. The goal was to obtain a better understand- ff Support for this study came from two NASA Grants (Award #: cient when compared to the two MW products. When comparing the ffi Ababa, Ethiopia, 2003–2007. evaluation of GPCP one-degreeAppl. daily Meteorol., rainfall 44(5), estimates 665–681, over 2005. the Mississippi River Basin, J. high-resolution satellite rainfall products4097–4110, over complex doi:10.1080/01431160701772526, terrain, 2008. Int. J. Remote Sens., 29(14), Mountainous Regions of Africa andface South Hydrology, America, edited in: by: Satellite Gebremichael, RainfallMedia M. Applications B. for and V., Sur- 193–204, Hossaim, 2010. F., Springer Science and seasonal rainfall in Ethiopia,2008. Int. J. Climatol., 28(13), 1723–1734, doi:10.1002/joc.1623, Water Resources and IrrigationInstitute, Development Colombo, in Sri Ethiopia, Lanka, International 2007. Water Management Terrain and Humid Tropical RegionHydrology, in edited by: Ethiopia, Gebremichael in: M., Satellite andB. Hossain, Rainfall V., F., 2009. Applications Springer Science for Surface The three products, regardless of the estimation technique (MW or IR), capture the In our assessment we found that both the MW and IR products were season inde- This study has found that all three products capture the varied spatial precipitation Ethiopian Meteorological Agency (EMA): Monthly RainGebremichael, Gauge M., Data Krajewski, (2003 W. to F., Morrissey, 2007), M., Addis Hu Dinku, T., Connor, S. J., and Ceccato, P.: Comparison of CMORPH and TRMM-3B42 over Dinku, T., Chidzambwa, S., Ceccato, P., Connor, S. J., and Ropelewski, C. F.: Validation of Cheung, W., Gabriel, H., Senay, B., and Singh, A.: Trends and spatial distribution of annual Bitew, M. M. and Gebremichael, M.: Evaluation Through Independent Measurements: Complex Awulachew, S. B., Yilma, A. D., Loulseged, M., Loiskandl, W., Ayana, M., and Alamirew, T.: Acknowledgements. NNX08AR31G and NNX10AG77G) to the University of Connecticut. References curate seasonal totals in theBaro three Akobo), river basins while to CMORPHtotals the and in northwest the (Awash, TMPA river Blue 3B42RT basins Nile provided to and more the southeast. accurate seasonal 1500 m) there was a large variation in the performance – PERSIANN provided more ac- precipitation at higher elevations (greater than 1500 m). At lower elevations (less than temporal patterns reported by studies suchconsistently as Seleshi reporting et higher al. (2004), monthly withhigher TMPA totals monthly 3B42RT totals than when CMORPH, compared and to PERSIANN. CMORPH reporting pendent in their performance withboth respect the to Kiremt elevation, with and similaraverages the of results Belg the reported three within for SREs eachwe were of compared found the to that those six of in river the general basins. ground PERSIANN based When rain has the gauges, a long-term tendency to underestimate the seasonal spatial pattern of the twototal; MW products, the TMPA 3B42RT number records ofof a rainy greater the mean days three annual recorded SREssimilar are to spatial nearly the patterns identical. rain of gaugeswhile the Comparing the spatially, Bias the IR we ratio, product results found with underestimated that each over performing MW nearly better the products in entire exhibited country. the northwest, ing of how thesecompared SREs, to CMORPH, ground PERSIANN based rain and gauges TMPA in 3B42RT, performed mountainous regions. when pattern over the mountainousitation northwest, and and the rainy homogeneous days(CMORPH mean in and annual the TMPA precip- lower 3B42RT), elevation arecipitation of and well rainy the correlated days, southeast. with in thecorrelation both only The coe spatial IR two product mean MW (PERSIANN), annual showing products pre- a decrease in The characteristics of precipitationprovided (mean by three annual high total resolutionterns, and SREs number for has of six been presented, rainy regionsand along days) temporal that with similarities as surround temporal and pat- the di Ethiopian Highlands so as to identify spatial 4 Conclusions 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 7684 7683 , D. 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V.: Precipitation Estimation from Remotely Hong, Y., Gochis, D., Cheng, J., Hsu, K., and Sorooshian, S.: Evaluation of PERSIANN-CCS Hirpa, F. A., Gebremichael, M., and Hopson, T.: Evaluation of High Resolution Satellite Pre- Gottschalck, J., Meng, J., Rodell, M., and Houser, P.: Analysis of Multiple Precipitation Products 5 5 30 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 mm/day to Tian et al. − 7686 7685 CMORPH (11%) CMORPH (9%) PERSIANN-CCS (49%) PERSIANN significantly underestimates at higher elevations. Does not exhibit elevation-dependent trends central CONUS; underestimates over theduring northeast the summer. Severe underestimationwestern over and north east during winter months. CONUS and mountain west duringmonths. fall and winter TMPA 3B42RT overestimate total precipitation over central CONUS and mountain westsummer during months. spring Overestimation and over mountainduring west fall and winter. United States,North America in winterNorth AmericaSouth America network. Occidental,Northwest Mexico, assessed, except one, whichNorth underestimated America by 1%. exhibits elevation-dependant bias (2008) underestimates light precipitation at higher elevations; (2007) (2008) North America CMORPH severely overestimates precipitation over North America summer months. Underestimation over central Evaluations on high resolution satellite product. Continued. Rainfall productEvaluated RegionCMORPHTMPA 3B42 V6 States (CONUS), Continental United Main results 1 TMPA mm/day) 3B42 for has both near summer zero and biases winter ( months.PERSIANNTMPA 3B42RT States Continental (CONUS), (2007) United PERSIANN overestimate central total CONUS precipitation and over mountain west during spring and (2005) Gottschalck et al. Reference Rainfall productEvaluated RegionCMORPHTMPA 3B42RTTMPA 3B42 Ethiopia, Africa Western HighlandsCMORPHTMPA 3B42RT Main Occurrence results of rainTMPA underestimated Total 3B42 amount by underestimated all by products TMPA Columbia, 3B42 (14%); Highlands,CMORPH (2010) South DinkuPERSIANN-CCS America et al. Ethiopia, AfricaCMORPH Berressa Total Watershed, amount underestimated OccurrencePERSIANN by TMPA of 3B42RT all rain (17%), products; Both underestimated TMPA underestimate 3B42 byTMPA heavy (16%) all overestimated 3B42RT Both rainfall and by products underestimate by TMPA 50% total 3B42RT (13%) rainfall; CMORPH and (32%), Great Rift Ethiopia, Valley, Africa Dinku et al. (2009) (2010) TMPA 3B42 TMPA V.6 3B42RT and CMORPHCMORPH show dependent elevation- trends, with Mainland underestimation Bitew China, at etCMORPH higher al. Reference Asia Overestimate rainfall Hirpa (2009) less et thanCMORPH al. 1 mm/day Oklahoma,PERSIANN elevations TRMM 3B42 Sierra Madre Occidental,TMPA 3B42 V.6 Northwest Mexico, Positively biased in summer, negatively La biased Yu Plata Underestimate etPERSIANN-CCS Basin, rainfall al. greater than TRMM 1 3B42 mm/day. Sierra closely Madre agrees CMORPH with and the PERSIANN rain overestimate gauge precipitation the rate and frequency. Overestimation Zeweldi by et 3%–13% al. for all sub basins (2009) Overestimates precipitation at low elevations, Nesbitt et al. Su et al. Hong et al. (2008) Table 1. Table 1. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 2 7688 7687 Elevation (m) Elevation (m) ) Min Max Min Max 1 2 of rain precipitation (km Area gauges (mm) Belg Kiremt River basin Number Mean annualAwash SeasonalBaro contribution AkoboBlue NileGenale DawaRift 11 Valley 16Wabi Shebele 11 37 1465 13 12 585 340 1305 29% 365 28% 650 56% 16% 52% 51% 47% 66% 12% 75% 31% 29% River basin Drainage Range of riverAwash basinBaro Range Akobo of rain gauge Blue NileGenale Dawa 75Rift 912 112 Valley 696 171 042Wabi 400 Shebele 199 812 160 0 480 202 697 52 3220 739 175 4375 455 4175 4250 1460 4240 1066 4175 376 902 2310 295 2840 1260 2354 3040 2940 2480 River basin precipitation characteristics. River basin drainage area and topography. Average of CMORPH, PERSIANN and TMPA 3B42RT estimates. Drainage area from Awulachew et al. (2007). 2 Table 3. 1 Table 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

= 733 mm/733 = yr mm/631 = yr days 70 =yr / days 54 =yr / 196 m 196 Rainy Days Rainy 4,517 m 4,517 - TMPA 3B42RT TMPA E Mean Std Mean Std 2,800

ual ual (f) (c) 240 44 2,400 Rain Gauges Rain 200 Shebele 2,000 E f) Mean Ann Mean f)

mean annual rainy days (precipitation – 160 42 1,600 = 499 mm/499 = yr mm/401 = yr days 56 =yr / days 39 =yr / Wabi Associated Associated (d–f) 120 Awash Dawa PERSIANN and and 1,200 Mean Std Mean Std E

(b) (e) 80 7690 7689 40 (mm / (mm year), (d

800 Mean Mean Annual Precipitation (mm/ year) 40 Mean Mean Annual Rainy Days (days year) / Genale (precipitation (precipitation greater 1 mm than day) / < Evaluated Evaluated < 400 < E

38 Precipitation = 68 days days 68 =yr / days 52 =yr / = 637 mm/637 = yr mm/540 = yr CMORPH Annual Annual Mean Std Mean Std E

(d) (a) 36 Mean Mean c) c)

– (precipitation greater than 1 mm / day) 1 greaterthan (precipitation mm (a (a

Rift Valley Rift E – Blue Nile Blue

Mean annual precipitation (mm/year), River Basins of Ethiopia Ethiopia of River Basins 2 34 Baro Akobo Six Six 1 mm / day) / mm 1 Rainy DaysRainy Precipitation

(greater than (greater Mean Annual Annual Mean Mean Annual Annual Mean – Six river basins of Ethiopia evaluated and associated rain gauges. Figure Figure

2 N N N N N N N N N N N N N

9 7 6 4 3 8 5 15 14 13 12 10 11 Fig. 2. (a–c) greater than 1 mm/day). Fig. 1. Figure Figure

717 445 414 65.9 26.9 33.4 47.8 13.5 55.5 3B42RT 3B42RT 3B42RT 1.50 1.25 0.50 1.75 1.00 0.75 - - - 9.3 – – – 439 229 65.8 28.4 256 24.9 56.2 57.7

PERSIANN PERSIANN PERSIANN 1.50 1.50 0.75 0.50 1.25 1.25 1.00 0.25 River Basin River Mean Mean Annual River BasinRiver

2007)

Precipitation Bias – 592 65.2 27.5 394 372 33.1 48.0 13.7 55.5 2007)

Dawa CMORPH CMORPH CMORPH – Shebele Awash River BasinAwashRiver TMPA 3B42RT TMPA Genale Wabi (%) (%) (%) (%) (%) (%) = 1.05 = 0.21 = = 0.57 = 0.15 = (f) = 0.89 = 0.18 = (b) (d) Mean Annual (mm) Annual Mean Kiremt Belg Mean Annual (mm) Annual Mean Kiremt Belg (mm) Annual Mean Kiremt Belg Mean Std Mean Std Mean Std CMORPH PERSIANN PERSIANN TMPA 3B42RT TMPA 7692 7691 73.6 17.4 806 29.2 45.9 53.2 28.3 1,630 1,762 3B42RT 3B42RT 3B42RT 911 437 77.6 14.2 27.3 50.3 50.0 29.3 1,059 CMORPH PERSIANN PERSIANN PERSIANN RiverBasin 706 73.8 17.0 30.1 45.2 53.0 28.1 1,370 1,578 CMORPH CMORPH CMORPH Akobo Blue Nile River BasinBlueRiverNile Rift Valley River BasinRiver ValleyRift Baro Mean Annual Precipitation Bias, 5 Year Average (2003 Bias, Precipitation Average 5 Annual Year Mean

(%) (%) (%) –

(%) (%) (%) (c) (e) (a) 4 Temporal Precipitation Pattern, 5 Year Monthly (2003 Pattern, Precipitation Monthly Average 5 Year Temporal Mean Annual (mm) Annual Mean Kiremt Belg Mean Annual (mm) Annual Mean Kiremt Belg Mean Annual (mm) Annual Mean Kiremt Belg – (c) (b) (a)

3 Figure Figure Precipitation (mm) Precipitation Figure Figure

0.76 0.78 0.71 0.69 0.87 0.68 0.58 0.63 0.57 0.02 ------No. of Gauges = 11 Gauges ofNo.= No. of Gauges = 11 Gauges ofNo.= No. of Gauges = 13 Gaugesof No.= No. of Gauges = 16 Gaugesof No.= No. of Gauges = 16 Gauges ofNo.= 13 Gaugesof No.= 0.17, R = 0.13 R= 0.17, 0.11, R = 0.59 R= 0.11, 0.12 R= 0.24, 0.38, R = = R 0.38, 0.20, R = 0.21 = R 0.20, 0.29, R = = R 0.29, 0.09, R = 0.89 = R 0.09, 0.63 = R 0.21, 0.14, R = 0.21 = R 0.14, 0.36, R = = R 0.36, 0.20, R = = R 0.20, 0.18, R = 0.67 = R 0.18, 0.38, R = = R 0.38, 0.12, R = = R 0.12, 0.28, R = R= 0.28, 0.39, R = R= 0.39, 0.17, R = = R 0.17, 0.13, R = R= 0.13, ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± River BasinRiver River BasinRiver River BasinRiver River Basin River 0.47 0.47 0.61 0.61 0.56 0.16 0.16 0.34 0.34 0.53 0.53 0.52 0.32 0.32 0.18 ------Dawa Dawa Shebele Shebele Awash River BasinAwashRiver Awash River BasinAwashRiver TMPA 3B42RT TMPA TMPA 3B42RT TMPA Genale Genale Wabi Wabi PERSIANN Slope = 0.10 0.10 = Slope PERSIANN 0.05 = Slope 3B42RT PERSIANN Slope = 0.13 0.13 = Slope PERSIANN 0.21 = Slope 3B42RT CMORPH Slope = 0.07 0.07 = Slope CMORPH CMORPH Slope = 0.20 0.20 = Slope CMORPH CMORPH Slope = 0.06 0.06 = Slope CMORPH 3B42RT Slope = 0.04 0.04 = Slope 3B42RT PERSIANN Slope = 0.00 0.00 = Slope PERSIANN PERSIANN Slope = = Slope PERSIANN = Slope 3B42RT PERSIANN Slope = = Slope PERSIANN = Slope 3B42RT PERSIANN Slope = = Slope PERSIANN = Slope 3B42RT CMORPH Slope = = Slope CMORPH CMORPH Slope = = Slope CMORPH CMORPH Slope = = Slope CMORPH (f) (f) (d) (b) (b) (d) Season (Belg). Based on river basins with basins Season on (Belg). river Based

PERSIANN PERSIANN 7694 7693

Elevation (m) Elevation (m) 0.65 0.61 0.15 0.53 0.61 0.04 0.06 0.28 0.40 0.13 0.52 0.56 0.08 0.04 0.41 0.05 ------R = = R R = = R R = = R No. of Gauges = 12 Gauges= ofNo. No. of Gauges = 12 Gaugesof= No. No. of Gauges = 37 Gauges= ofNo. 11 Gaugesof= No. No. of Gauges = 11 Gaugesof= No. No. of Gauges = 37 Gaugesof= No. 0.69, R = 0.02 = R 0.69, 0.22, 0.22, 0.26, R = = R 0.26, 0.61, R = 0.01 = R 0.61, 0.12, R = = R 0.12, 0.35, 0.35, 0.31, R = = R 0.31, 0.42, R = = R 0.42, 0.15, R = = R 0.15, 0.17, R = = R 0.17, 0.26, R = = R 0.26, 0.43, 0.43, 0.39, R = = R 0.39, 0.57, R = = R 0.57, 0.17, R = = R 0.17, 0.52, R = = R 0.52, 0.30, R = = R 0.30, 0.70, R = R= 0.70, ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± CMORPH CMORPH RiverBasin RiverBasin 0.65 0.65 0.03 0.03 0.33 0.33 0.51 0.51 0.79 0.18 0.18 0.07 0.07 0.06 0.12 0.12 0.26 0.26 0.34 0.03 0.03 0.09 0.09 0.22 0.06 0.06 0.04 0.04 ------Akobo Akobo Blue Nile River BasinBlueRiverNile Blue Nile River BasinBlueRiverNile Rift Valley River BasinRiver ValleyRift Rift Valley River BasinRiver Valley Rift Baro Baro 3B42RT Slope = 0.02 0.02 = Slope 3B42RT PERSIANN Slope = = Slope PERSIANN = Slope 3B42RT PERSIANN Slope = = Slope PERSIANN = Slope 3B42RT CMORPH Slope = 0.01 0.01 = Slope CMORPH PERSIANN Slope = = Slope PERSIANN PERSIANN Slope = = Slope PERSIANN = Slope 3B42RT PERSIANN Slope = = Slope PERSIANN = Slope 3B42RT 3B42RT Slope = = Slope 3B42RT CMORPH Slope = = Slope CMORPH CMORPH Slope = = Slope CMORPH PERSIANN Slope = = Slope PERSIANN CMORPH Slope = = Slope CMORPH CMORPH Slope = = Slope CMORPH CMORPH Slope = = Slope CMORPH (c) (e) (a) (c) (e) (a) Bias Bias Ratio vs. Elevation for the Major Rainy Season (Kiremt). Based on river basins with at least 10 or more rain gauges. at orwith rain 10 more least at least 10 or more rain gauges or rain at10 more least Bias Ratio vs. Elevation for the Minor Rainy the Minor Rainy Ratio for Elevation vs. Bias

–

6 5

Bias Ratio Bias Bias Ratio Bias Figure Figure Figure Figure Bias ratio vs. elevation for the major rainy season (Kiremt). Based on river basins with Bias ratio vs. elevation for the minor rainy season (Belg). Based on river basins with at least 10 or more rain gauges. Fig. 6. Fig. 5. at least 10 or more rain gauges.