Trend and variability of rainfall in Tigray, Northern Ethiopia: Analysis of meteorological data and farmers perception

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1 Academa Journal of Envronmental Scences 1(8): , October 2013 DOI: ISSN: X 2013 Academa Publshng Research Paper Trend and varablty of ranfall n Tgray, Northern Ethopa: Analyss of meteorologcal data and farmers percepton Accepted 17 th May, 2013 ABSTRACT Gebre Hadgu 1 *, Knde Tesfaye 2, Grma Mamo 3 and Belay Kassa 4 1Haramaya Unversty, College of Agrculture and Envronmental Scence, P. O. Box 138, Dre Dawa, Ethopa. 2Internatonal Maze and Wheat Improvement Center (CIMMYT), Adds Ababa, Ethopa. 3Ethopan Insttute of Agrcultural Research, Melkassa Agrcultural Research Center, Nazareth, Ethopa. 4Haramaya Unversty, College of Busness and Economcs, P. O. Box 138, Dre Dawa, Ethopa. *Correspondng author. E-mal: G.hadgu27@gmal.com. Tel: Ranfall s the most mportant but varable clmatc parameter n the sem-ard tropcs. In ths study, the trend and varablty of ranfall were compared wth the percepton of farmers n northern Ethopa. Daly ranfall data obtaned from fve meteorologcal statons located n dfferent agroecologcal zones were used to determne trends n annual and seasonal totals, onset and cessaton dates, length of growng perod (LGP) and dry spell length. Sen s estmator and Mann-Kendall's statstcal tests were used for trend detecton. Two hundred and ffty three farmers from three admnstratve areas (dstrcts) that are close to the meteorologcal statons were ntervewed n order to nvestgate farmers' percepton on ranfall trend and varablty n the study area. The results ndcate that ranfall n the regon s hghly varable wth a non-sgnfcant trend n both annual and seasonal totals for all statons. However, trends of ranfall events such as onset date, cessaton date, LGP, and dry spell length were changed sgnfcantly n most statons, whch agreed wth the farmers percepton. Moreover, most statons experenced drought condtons n the last decade. The results suggest the need for desgnng approprate agronomc and water management strateges to offset the negatve mpacts of ranfall varablty n the study area. Key words: Ranfall, ranfall trend, ranfall varablty, onset, length of growng perod. INTRODUCTION Agrculture plays a domnant role n the economy of Ethopa, contrbutng 41% GDP, 80% of the employment and the majorty of foregn exchange earnngs (Gebreegzabher et al., 2011). The success of agrcultural producton has, therefore, large mplcatons, rangng from the state of the countrywde economy to the survval of the subsstence farmers (Block and Rajagopalan, 2007). Natural ranfall s the man source of water for crop producton as rrgaton covers only 5% of the cultvated land n the country (Awulachew et al., 2010). Several studes (Hagos et al., 2009; Osman and Sauerborn, 2002) examned the mpact of ranfall varablty on the Ethopan economy, and found that ranfall varablty n the country led to a producton defct (20%) and ncrease n poverty rates(25%) whch cost the economy over one-thrd of ts growth potental. Assessng trends n ranfall characterstcs based on past records together wth the percepton of the local communty s essental to develop adaptaton strateges. Prevous studes dealng wth annual and seasonal ranfall trends n Ethopa revealed controversal results. Selesh and Demaree (1995); Osman and Sauerborn (2002) ndcated hgh ranfall varablty and ts negatve trend durng the man rany season (June to September).

2 Academa Journal of Envronmental Scences; Hadgu et al. 160 Table 1. Geographcal locatons and ranfall database of fve statons used n the study. Statons Alttude (m) Lattude ( N) Longtude ( E) Database perod Years wth mssng data Alamata , 1991 Adgudum Mekelle , 1990 Edagahamus Adgrat Usng data n the last half a century, NMSA (2001) reported a sgnfcant reducton n annual ranfall n the north, southwest part of the country whle there was an ncreasng trend of annual ranfall n the central part of Ethopa. Consderng ranfall data of the Amhara Regon (Northwest Ethopa), Bewket and Conway (2007) reported nconsstent results n the annual, kremt and Belg ranfall trends wthn the statons of the regon. The authors noted that for the perod of 1975 to 2003, kremt and annual ranfall shows sgnfcantly ncreasng trend at Desse and Lalbela whle Debre Tabor revealed sgnfcantly decreasng ranfall trend durng both seasons. On the other hand, Meze-Hausken (2004); Selesh and Camberln (2006) and Cheung et al. (2008) dd not fnd any sgnfcant trend over the northern and northeastern part of the country. Prevous studes on ranfall analyss concentrated on the central hghlands of the country (Selesh and Demar ee, 1995; Osman and Sauerborn, 2002; Cheung et al., 2008). Moreover, data obtaned from a sngle observatory staton have been used to study the spatal and temporal varablty of ranfall n the study regon (Meze-Hausken, 2004; Selesh and Zanke, 2004). However, as topography and elevaton of the regon s hghly varable, ths could easly mss localzed trends and varablty. Studes of ranfall varaton generally focusng on large areas would be of no use for local agrculture, partcularly n places where ranfall s hghly varable (Murugan et al., 2008). Although, nformaton on ranfall characterstcs n dry land areas s crtcal for agrcultural plannng, many studes (Meze-Hausken, 2004; Selesh and Zanke, 2004) used seasonal or annual totals for trend analyss. Nevertheless, farmers evaluate ranfall varablty n relaton to ther agrcultural practces based on ts amount, onset and cessaton at ntervals of days or even hours whch do not match wth results of ranfall analyss based on annual or monthly totals. As a result, there s a gap n relatng ranfall analyss wth the local farmers observaton who s the ultmate user of the fndng. Understandng farmers vews could offer mportant nsghts on the nature of envronmental processes that the analyss of scentfc data alone cannot capture (West et al., 2008). However, studes that nvolve both the analyss of hstorcal records and the percepton of the local farmers are not avalable n Ethopa. Therefore, the objectves of ths study were to analyze trends and varablty of ranfall parameters and to explore the relaton between the results of the hstorcal ranfall analyses and the percepton of farmers n northern Ethopa. METHODOLOGY Background of the study area The study was conducted n the northern escarpment of Ethopa located between 36 to 40 E longtude and 12.5 to 15 N lattude. It borders wth Eretra n the north, Sudan n the west, Amhara Regonal State n the southwest and Afar Regonal State n the east. The landform s complex composed of hghlands (n the range of 2300 to 3200 m.a.s.l) and lowland plans (wth an alttude n the range 500 to 1500 m.a.s.l). It has dversfed agro-ecologcal zones and nches each wth dstnct sol, geology, vegetaton cover and other natural resources. The clmate s manly sem-ard and for most of the regon, the man rany season (locally called kremt) lasts for 3 to 4 months, between June and md-september (Araya et al., 2010; Gebrehwot and van der Veen, 2013). Moreover, some part of the regon also gets a small ran shower (locally known as Belg) from February to May. There s great nter-annual spatal and temporal ranfall varaton. In all months, except the month of August, the decadal reference evapotranspraton (ET 0) exceeds the mean decadal ranfall (Araya et al., 2010). The area was chosen for the study because of recurrent drought and crop falures that are common n ths part of Ethopa (Gebrehwot and van der Veen, 2013). As the farmers n ths area have been experencng drought frequently, ther perceptons on drought are valuable. Daly ranfall data of fve statons, whch le wthn the dfferent agroecologcal zones of the regon were used for ths study. The statons together wth ther geographcal descrptons and length of database consdered are shown n Table 1 and Fgure 1. Data source Daly ranfall data of dfferent statons wth varous

3 Academa Journal of Envronmental Scences; Hadgu et al. 161 Fgure 1. Locaton of study statons. duraton were obtaned from the Natonal Meteorologcal Servce Agency (NMSA) of Ethopa, Mekelle Unversty, Tgray Agrcultural Research Insttute (TARI) and Bureau of Agrculture and Natural Resource n the respectve dstrcts. The statons were selected based on the length of a record perod and the relatve completeness of the data. The world meteorologcal organzaton has recommended 30 years as a mnmum data requred for searchng evdence of clmatc change n hydroclmatc tme seres (IPCC-TGCIA, 1999). Based on ths crteron, eght statons were dentfed. However, contnuous and long term database s hardly found n the study regon as t was a ste of conflct durng the past regme. Thus, consderng the maxmum flexble thresholds of 10% mssng values adopted by Ngongondo et al. (2011), only fve observatory statons remaned. On the other hand, to reconstruct the gap and to fll the mssng values, data were generated followng the frst order Markov chan model usng INSTAT plus (v3. 6) Software (Stern et al., 2006). Then, the generated data were checked for ther physcal representatve of the respectve ste. INSTAT plus was also used to summarze the daly data nto annual, monthly and seasonal totals and to analyze the onset and cessaton of the rany season and length of growng perod (LGP). Data qualty control Outler detecton Identfcaton of outlers (suspcous data) has been the prmary emphass to the clmate database development (Gonzalez-Rouco et al., 2001). Outlers are values greater than a threshold value of a specfc tme seres data that can affect the detecton of nhomogenety (Gonzalez-Hdalgo et al., 2009). For non-normally dstrbuted data lke ranfall, the Turkey fence s recommended for trmmng the outler (Ngongondo et al., 2011). The prmary objectve of outlers trmmng s to reduce the sze of the dstrbuton tals n order to make a safer use of the non-resstant homogenzaton technques used later (Gonzalez-Rouco et al., 2001). In ths partcular study, the Turkey fence outlned n the study of Ngongondo et al. (2011) was used to screen the outlers. The data range s represented as: Q.5* IQR, Q 1.5* IQR Where Q 1 and Q 3 are respectvely the lower and upper

4 Academa Journal of Envronmental Scences; Hadgu et al. 162 quartle ponts, 1.5 are standard devatons from the mean, and IQR s the nterquartle range. Values outsde the Turkey fence are consdered as outlers. In ths study, such outlers were set to a lmt value correspondng to ±1.5 IQR. Homogenety test The second step of the qualty control process nvolved a homogenety analyss. There are dfferent methodologes used to analyze homogenety. In ths partcular study, due to ts lower demands n applcaton and nterpretaton as well as, the poor correlaton between statons, cumulatve devaton test was used for absolute testng (usng statons own data). Ths method was commonly used n the clmatology to detect nhomogenetes n the meteorologcal tme seres (Sahn and Kerem, 2010; Ngongondo et al., 2011; Kang and Yusof, 2012). Bushand (1982) noted that tests for homogenety can be based on the adjusted partal sums or cumulatve devatons from the mean and t s gven as follows: 0 S 0 and Sk k 1 ( y y), k= 1,,n The term S k s the partal sum of the gven seres. If there s no sgnfcant change n the mean, the dfference between Y and Y wll fluctuate around zero. The sgnfcance of the change n the mean s calculated wth rescaled adjusted range R, whch s the dfference between the maxmum and the mnmum of the S values scaled by the sample standard devaton as: k R (max S k mn Sk ) / SD 0kn 0kn R / n s calculated by Then, the crtcal value for Bushand (1982) and for n=30, ts value s 1.5 and 1.4, respectvely for 5 and 10% probablty levels. Test of randomness and persstence It s well known that the tme seres data requred for trend analyss should be random and/or non-persstent (Ngongondo et al., 2011). Portal and Kahya (2006) noted that one of the problems n the analyss and nterpretaton of trends n hydrologcal data s the confoundng effect of seral dependence. Furthermore, n the presence of postve seral correlaton, the non-parametrc test could sgnfy a sgnfcant trend due to random effects of the data seres (Kulkarn and Van Storch, 1995). In ths study, before proceedng to trend analyss, the tme seres data was tested for randomness and ndependence usng the autocorrelaton functon (r 1) as descrbed n Box and Jenkns (1976) n the followng manner: r 1 n1 x xx 1 x 1 n x x 1 2 Where x s an observaton, x 1 s the followng observaton, x s the mean of the tme seres, and n s the number of data. In addton, Dahmen and Hall (1989) defned the crtcal regon at 5% probablty as follows: 1.96 ( n 2) /( n 1), ( n 2) 1 /( n 1) Seral correlaton of lag-1 (the correlaton of two consecutve observatons n the tme seres data) was employed n ths study. Whenever sgnfcant correlaton appeared n the data seres, the data seres has been prewhtened followng the procedure descrbed n Partal and Kahya (2006). The pre-whtened data seres may be obtaned as: ( x r x x r x,..., x r x ) 2 1 1, 3 1, 2 n 1 n1 Trend analyss Several tests are avalable for the detecton and estmaton of trends. In ths partcular study, Mann-Kendall s test was employed. Mann-Kendall s test s a non-parametrc method, whch s less senstve to outlers and test for a trend n a tme seres wthout specfyng whether the trend s lnear or non-lnear (Partal and Kahya, 2006; Yengun et al., 2008). The Mann-Kendall s test statstc s gven as: S N 1 N 1 j1 sgn x j x Where S s the Mann-Kendal s test statstcs; x and x j are the sequental data values of the tme seres n the years and j ( j > ) and N s the length of the tme seres. A postve S value ndcates an ncreasng trend and a negatve value ndcates a decreasng trend n the data seres. The sgn functon s gven as: sgn x x j 1 f 0 f 1 f ( x ( x j ( x j j x ) 0 x ) 0 x ) 0

5 Academa Journal of Envronmental Scences; Hadgu et al. 163 The varance of S, for the stuaton where there may be tes (that s, equal values) n the x values s gven by: Var ( S) 1 18 N( N 1) (2N 5) m 1 t ( t 1) (2t 5) Where m s the number of ted groups n the data set and t s the number of data ponts n the th ted group. For n larger than 10, Z MK approxmates the standard normal dstrbuton (Partal and Kahya, 2006; Yengun et al., 2008) and computed as follows: Z MK S 1 Var ( S) f 0 f S 1 Var ( S) f S 0 S 0 S 0 The presence of a statstcally sgnfcant trend s evaluated usng the Z MK value. In a two-sded test for trend, the null hypothess H o should be accepted f Z MK Z1 / 2 at a gven level of sgnfcance. Z 1- α/2 s the crtcal value of Z MK from the standard normal table. For example, for 5% sgnfcance level, the value of Z 1- α/2 s Sen s estmator of slope Ths test s appled n cases where the trend s assumed to be lnear, depctng the quantfcaton of changes per unt tme. Ths method could be used wth mssng data and reman unaffected by outlers or gross errors (Karpouzos et al., 2010). The slope (change per unt tme) was estmated followng the procedure of Sen (1968). A detaled outlne of the procedure s gven n Partal and Kahya (2006) and Karpouzos et al. (2010). Based on the aforementoned procedure trends of annual, seasonal (kremt and belg) and monthly (June to September) totals as well as, ranfall characterstcs such as onset date, cessaton date, LGP, number of rany days and dry spell length were determned. Therefore, the ranfall characterstcs of each staton were frst set as: Onset and cessaton date: Dfferent authors use dfferent threshold values to determne the onset of the ran. The crteron used n ths study was a ranfall of 20 mm or more accumulated over three consecutve rany days after a specfed date (n ths case July frst) wth no dry spell greater than 7 days n the next 30 days (Tesfaye and Walker, 2004). Moreover, the end of the season was defned as the date when the avalable sol water content dropped to 10 mm m -1 of avalable water (Tesfaye and Walker, 2004) after September 11. Ths date was set based on farmers nformaton obtaned durng prelmnary survey. The length of growng perod was calculated as a dfference between the onset date and date of the end of the season. Number of rany days and dry spell length: Based on the defnton of Natonal Meteorologcal Servce Agency of Ethopa, a day s consdered as a rany day f t accumulates 1 mm or more ranfall (NMSA, 2001). The number of rany days was, therefore, counted startng from the frst day of June to September 31 (kremt season) n each year. Moreover, maxmum number of consecutve dry days (a day that accumulate ranfall <1 mm) were counted to determne dry spell length n kremt season. Varablty analyss Standardzed anomaly ndex, precptaton concentraton ndex and coeffcent of varaton were used as descrptors of ranfall varablty (Bewket and Conway, 2007; Ayalew et al., 2012). Standardzed Anomaly Index (SAI) was calculated as the dfference between the annual total of a partcular year and the long term average ranfall records dvded by the standard devaton of the long term data. Ths ndex used to examne the nature of the trends also makes possble the determnaton of the dry and wet years n the record. Its formula s gven as: ( x ) Where, Z s standardzed ranfall anomaly; x s the annual ranfall total of a partcular year; µ s mean annual ranfall over a perod of observaton and s the standard devaton of annual ranfall over the perod of observaton. Precptaton Concentraton Index (PCI) was analyzed usng De Luı s et al. (1999), whch s the modfed verson of Olver s (1980). It was computed as: PCI 12 1 P 2 / 12 1 P 2 x100 Where, P s the ranfall amount of the th month. PCI values below 10 ndcate unform monthly ranfall dstrbuton; values between 11 and 20 ndcate hgh concentratons of monthly ranfall dstrbuton; and values of 21 and above ndcate very hgh concentraton of monthly ranfall dstrbuton. Coeffcent of varaton (CV) was calculated to evaluate the varablty of the ranfall and ts characterstcs by dvdng the standard devaton of the event to ts mean. Farmers percepton To compare meteorologcal data wth the percepton of farmers at the ground, survey was conducted n three

6 Academa Journal of Envronmental Scences; Hadgu et al. 164 Table 2. Average seasonal ranfall contrbutons to annual ranfall totals n Northern Ethopa, 1980 to Statons Annual ranfall (mm) Kremt ranfall (mm) Belg ranfall (mm) Alamata (50%) 270 (36%) Adgudum (89%) 46 (09%) Mekelle (81%) 97 (16%) Edagahamus (62%) 216 (31%) Adgrat (62%) 171 (29%) Percentage contrbuton to annual ranfall s gven n parentheses. Table 3. Coeffcent of varaton for annual, kremt and belg ranfall and mean PCI values for the perod 1980 to 2009 n Northern Ethopa. Statons Annual Man ran season Small ran season PCI (%) Alamata Adgudum Mekelle Edagahamus Adgrat PCI s precptaton concentraton ndex. dfferent dstrcts (admnstratve unt equvalent to dstrct) of Tgray regon. Durng the study, three dstrcts havng long term meteorologcal data records were selected purposvely. Smlarly, two peasant assocatons (the smallest admnstratve unt) neghborng the meteorologcal statons, from each dstrct were agan purposvely selected. In the thrd stage, a total of 253 farm households was sampled randomly proportonal to the sample szes of each peasant assocaton. Structured and sem-structured ntervew schedules were used to collect the prmary data on the perceptons of the household on ranfall trends and varablty. Fnally, data obtaned from the sample households were subjected to statstcal analyss. Descrptve statstcs such as percentage and frequency of occurrence were used to assess farmers percepton on the ranfall trend and varablty. RESULTS AND DISCUSSION Annual and seasonal ranfall regmes Ranfall n the study area s generally low that vares slghtly from 509 mm at Adgudum to 752 mm at Alamata (Table 2). The man rany season (kremt ranfall) contrbutes largely to the annual ranfall totals n all statons. However, ts contrbuton vares from 50 to 90% dependng on the ste of the locaton. Belg ranfall also makes a consderable contrbuton to the annual ranfall totals n some areas such as Adgrat (29%), Edagahamus (31%) and Alamata (36%). Smlarly, n the Amhara regonal state of Ethopa, kremt and belg ranfall had contrbuted 55 to 85% and 8 to 24%, respectvely to the annual ranfall totals (Bewket and Conway, 2007; Ayalew et al., 2012). The coeffcent of varaton n most statons revealed that ranfall n the regon has hgh nter-annual varablty (Table 3). The result ndcated that annual ranfall at Adgudum (CV>40%) and at Edagahamus (CV>70%) was extremely varable. Moreover, kremt ranfall varablty for most statons was also hgh (CV nearly >30%). In contrast, Bewket and Conway (2007) reported moderate nter annual varablty of kremt ranfall n the Amhara regonal state of Ethopa. Consderng the drect effect of kremt ranfall on agrcultural producton, hgh varablty could tremendously affect the lvelhood of the farmng communty n the regon. Lkewse, belg ranfall n the regon showed hgh nter annual varablty (CV>50%). Comparng the seasonal varablty of ranfall n the regon, belg ranfall s more varable than the kremt ranfall. Selesh and Zanke (2004) and Bewket and Conway (2007) reported smlar results. Selesh and Zanke (2004) noted that the ranfall varablty over the central hghland of Ethopa durng the kremt season was assocated wth the equatoral eastern Pacfc sea level pressure, the southern oscllaton ndex and the sea surface temperature (SST) over the tropcal eastern Pacfc Ocean. These authors further noted that the SST over the tropcal eastern Pacfc Ocean s negatvely correlated wth kremt ranfall. Moreover, analyss of PCI value revealed that all statons have greater than 20% (Table 3). Based on the scale

7 Academa Journal of Envronmental Scences; Hadgu et al. 165 defned n De Luı s et al. (1999), the statons are grouped under hgh and very hgh concentraton whch ndcates poor monthly dstrbuton of the ranfall. A smlar result was also ndcated n Bewket and Conway (2007) and Ayalew et al. (2012) wheren the ranfall n the Amhara regon of Ethopa s characterzed by hgh to very hgh monthly concentraton. Standardze anomaly ndex (SAI) Analyss of the standard anomaly ndex for the statons s depcted n Fgure 2. The ranfall pattern n the studed statons exhbts certan characterstcs that a dry year s followed by another two or three dry years and vs-à-vs for the wet years. The study revealed that many of the statons have experenced drought durng 1980s and 2000s. Generally, for the perod 1980 to 2009, the number of years recorded below the long term average at Alamata, Adgudum, Mekelle, Edagahamus and Adgrat were 43, 47, 50, 43 and 57%, respectvely. However, frequency occurrence of below normal ranfall ncreased n the last decade. In ths regard, 60% of the years n the recent decade had recorded below long term average n all statons. Moreover, durng the last 30 years, 1984 was the drest years at Alamata, Adgudum and Mekelle whle for Edagahamus and Adgrat t was 1990 and 1999, respectvely. Bewket and Conway (2007) and Ayalew et al. (2012) had used SAI to demonstrate the ntensty and frequency of drought at varous tme scales and reported as helpful to ndcate the drought characterstcs. Trend analyss of ranfall elements Annual and seasonal ranfall trends The Mann Kendall trend test shows a decreasng trend of annual ranfall n most of the statons (Table 4). In the last three decades, at the statons of Alamata, Adgudum, Mekelle and Edagahamus, annual ranfall had decreased by 43.8, 141.9, and mm, respectvely. The staton of Adgrat, on the other hand, had ndcated an ncreasng trend of annual ranfall. However, both ncreasng and decreasng trends of annual ranfall totals were not statstcally sgnfcant. Ths mght be due to large nterannual fluctuaton of ranfall n the regon. For nstance, at Alamata and Adgrat, the 1980s were generally a dry perod relatve to the precedng decade and ranfall recovered to more humd condtons durng the 1990s that agan decreased to below long term average n the 2000s (Fgure 2). Thus, analyss that ends durng the late 1980s or early 1990s mght show a declnng trend, whereas, f the perod s extended, the trend n annual ranfall totals could reduce and/or removed. On the other hand, ranfall at Mekelle, Adgudum and Edagahamus showed consecutve 2 to 3 year perods wth wet and dry years alternatvely wth no apparent trend. Ths result agrees wth the fndngs of Conway (2000), Selesh and Zanke (2004), Cheung et al. (2008) and Vste et al. (2012) that ndcates non-sgnfcant trend of annual and seasonal ranfall totals n northern Ethopa. Lkewse, statons of Adgudum, Mekelle and Adgrat had revealed a decreasng trend of kremt ranfall totals whle Alamata and Edagahamus had shown an ncreasng trend. Moreover, all statons durng belg season showed decreasng trend (Table 4). The negatve trend at Alamata and Edagahamus was statstcally sgnfcant at 10% probablty level. Overall, the drecton and magntude of the seasonal ranfall trend was not unform. Bewket and Conway (2007) and Ayalew et al. (2012) had also reported smlar results, wheren the drecton and magntude of the trend n seasonal ranfall n Amhara regonal state of Ethopa vares from staton to staton. The major drvng factors that nfluence ranfall patterns n Ethopa are the equatoral eastern Pacfc sea level pressure, the southern oscllaton ndex and the sea surface temperature (SST) over the tropcal eastern Pacfc Ocean (Selesh and Zanke, 2004). However, wthn the regons of Ethopa, ranfall s governed wth elevaton (Conway, 2000). Ths nconsstent trend of the stuatons mght also be the man reason for these studes that reported non-sgnfcant trend of annual and season ranfall over the country n general and n the regon n partcular. Monthly ranfall trends Consderng ranfall durng months of the man growng season (June to September), decreasng trends had observed at Adgudum n all growng months (Table 5). Lkewse, except the month of June, ranfall at Mekelle also revealed a decreasng trend n all months of the growng season. On the other hand, despte the varablty of the statons wth regard to the magntude and drecton of trends, a negatve trend had observed n all statons durng the month of September. Ths ndcates contracton of the LGP and ncrease n termnal drought. However, nether of the trends was statstcally sgnfcant. Trends n long term characterstcs of kremt ranfall Onset date The medan for onset of kremt ranfall s smlar n all statons and t begns on the frst week of July (Table 6). It was also characterzed wth hgh standard devaton (> 10 days). Ths hgh standard devaton, partcularly at Alamata and Edagahamus, mples that patterns could not be easly understood and consequently, decsons pertanng to crop

8 Academa Journal of Envronmental Scences; Hadgu et al. 166 Fgure 2. Standardzed tme seres plot of annual ranfall totals of fve satons n northern Ethopa over the perod 1980 to 2009.

9 Academa Journal of Envronmental Scences; Hadgu et al. 167 Table 4. Trends of annual and seasonal ranfall totals n northern Ethopa for the perod 1980 to Statons Annual Kremt season Belg season ZMK slope ZMK Slope ZMK Slope Alamata ns ns * Adgudum ns ns ns Mekelle ns ns ns Edagahamus ns ns * Adgrat 0.07 ns ns ns ZMK s Mann Kendall trend test, Slope (Sen s slope) s the change (mm)/annual; ns s non-sgnfcant trend at 0.05 and 0.1 and * ndcates sgnfcant trend at 0.1 sgnfcant level Table 5. Trends of monthly (June-September) ranfall totals n northern Ethopa for the perod Statons June July August September ZMK Slope ZMK Slope ZMK Slope ZMK Slope Alamata 0.51 ns ns ns ns Adgudum ns ns ns ns Mekelle 0.87 ns ns ns ns Edagahamus ns ns ns ns Adgrat 0.05 ns ns ns ns ZMK s Mann Kendall trend test, Slope (Sen s slope) s the change (mm)/annual; ns s non-sgnfcant trend at 0.05 and 0.1. plantng and related actvtes should be taken wth great care. Furthermore, the result also ndcated that the onset date n the last 30 years was sgnfcantly changed n most statons. In ths regard, the ran at Alamata, Adgudum, Mekelle, Edagahamus and Adgrat has come on average 3 to 7 days per decade. On the other hand, Araya and Stroosnjder (2011) had presented smlar result that the onset of Kremt ranfall at Alamata, Adgudum, Machew and Mekelle was the frst decade of July. Cessaton date Kremt ranfall n the studed statons ceased startng from the frst week of September (at Edagahamus) to frst week of October (at Mekelle) (Table 6). Araya and Stroosnjder (2011) had also reported smlar fndngs n northern Ethopa. The result further ndcated that kremt ranfall had ceased early n the northeast part of the regon as compared to the south and southeast parts. The medan date of the end of the kremt season was characterzed by low standard devaton (<10 days) at Adgudum, Mekelle and Adgrat and hence, the end of rany season n these statons s relatvely stable. In contrast, end of the kremt season at Alamata and Edagahamus showed hgh standard devaton (about 20 days), whch mples dffculty n understandng the pattern of end of the rany season. Hence, decsons related to termnal drought management practces and crop harvestng actvtes requres great care. Moreover, a decreasng trend has been observed n cessaton of kremt ranfall n most statons. Partcularly, the trend at Adgudum and Mekelle was statstcally sgnfcant. In contrast, an ncreasng trend of Kremt ranfall cessaton has been observed at Edagahamus. Length of growng perod (LGP) Average length of growng perod n the study regon vares from 66 to 85 days dependng on the locaton of the staton (Table 6). Mekelle and Alamata had respectvely, 85 and 79 days of LGP as compared to Edagahamus, whch had only 66 days. The coeffcent of varaton at Alamata (28%) and Edagahamus (29%) also showed hgh year to year varablty of LGP. In contrast, Adgudum, Mekelle and Adgrat had recorded low coeffcent of varaton (<20%) n LGP, whch can help to plan the type of crops grown based on ther maturty perod. On the other hand, all statons revealed that LGP has become reduced n the last three decades. The decreasng trend n LGP at Alamata, Adgudum, Mekelle and Adgrat was statstcally sgnfcant. Based on the present result for the perod (1980 to 2009), LGP decreased by 27.6, 25.8, 24.3 and 13.2 days, respectvely for Alamata, Adgudum, Mekelle and Adgrat. Correlaton analyss of LGP wth onset date and end of rany date showed a strong relatonshp n all statons (data not showed). The short LGP at Edagahamus

10 Academa Journal of Envronmental Scences; Hadgu et al. 168 Table 6. Statstcal characterstcs and trends of onset date, cessaton date and LGP at fve statons over the perod 1980 to 2009 n Northern Ethopa. Ranfall characterstcs Onset date Statons statstcs Alamata Adgudum Mekelle Edagahamus Adgrat Medan July 4 July 12 July 11 July 3 July 5 ZMK 2.52** 2.11** 2.81** 0.78 ns 2.13** Slope SD Cessaton date Medan Sept-21 Sept-20 Oct-4 Sept-8 Sept-16 ZMK ns -2.19** -1.80* 0.75 ns ns Slope SD LGP (days) Medan ZMK -2.57** -2.59** -3.07** ns -1.78* Slope CV (%) ZMK s Mann Kendall trend test, Slope (Sen s slope) s the change (mm)/annual; **,* s statstcally sgnfcant at 0.05 and 0.1 probablty level; ns s non-sgnfcant trend at 0.1; SD s standard devaton; CV s coeffcent of varaton Edagahamus therefore, resulted due to early cessaton of ranfall n the area. Number of rany days Average number of annual rany days and maxmum dry spell length observed n kremt season at fve statons over the perod 1980 to 2009 s depcted n Table 7. The number of annual rany days observed n the study regon vares from 50 days (at Adgudum) to 66 days (at Alamata). In lne wth ths, the number of annual rany days at Mekelle was 61 days and ts trend was non-sgnfcant over the perod 1965 to 2002 (Selesh and Zanke, 2004). In regard to the nter-annual varablty, number of rany days recorded at Alamata, Adgudum and Edagahamus had observed hgher varablty (CV=20%) as compared to other statons. On the other hand, the Mann-Kendall s trend test n the number of rany days ndcated that most statons revealed decreasng trend. The trend at Alamata was sgnfcant, whch decreased by 6.8 days per decade. However, the number of rany days at Mekell ncreased by 1.5 days per decade. Selesh and Zanke (2004) had also reported non-sgnfcant trend of rany days from ten statons n Ethopa. Dry spell length The average length of dry spell durng the kremt season over the regon was generally long that ranged from 21 days at Mekelle to 26 days at Alamata and Edagahamus (Table 7). It ndcated that the average length of dry spell durng kremt season had a low standard devaton (<10 days) n most of the statons studed (Table 7). Ths mples that the occurrence of a dry spell length ndcated at each staton durng the kremt season at least once s certan. The result further revealed that the dry spell length durng kremt season showed an ncreasng trend n all statons. The trend was statstcally sgnfcant for most statons. Hence, t could be helpful to devse agronomc practces that retan mosture at the plant root zone and reduce crop falure due to extended dry spell. Selesh and Camberln (2006) also reported smlar results that longer dry spell was observed n the northern (Mekelle, 20.3 days) and eastern (Jjga, 16.2 days) part of the country. Under dry land condtons where nter-annual and nter-seasonal varablty of ranfall s hgh, analyss of trends n ranfall events such as onset, cessaton, LGP, dry spell length and number of rany days mght be more mportant than annual and seasonal totals. Percepton of farmers on annual and seasonal ranfall trends Percepton of farmers on trends and varablty of seasonal and annual ranfall totals and ts dstrbuton s presented n Table 8. The results showed that more than 92% of the farmers at Adgrat perceved a decreasng trend of annual, kremt and belg ranfall totals. Lkewse, about 73.4% of the farmers at Mekelle notced a decrease n annual and kremt

11 Academa Journal of Envronmental Scences; Hadgu et al. 169 Table 7. Statstcal characterstcs and trends of dry spell length and rany days at fve statons over the perod 1980 to 2009 n Northern Ethopa. Ranfall characterstcs Rany days Statons Statstcs Alamata Adgudum Mekelle Edagahamus Adgrat Mean ZMK -1.8* ns 0.52 ns ns ns Slope CV (%) Dry spell length (days) Mean ZMK 2.84* 1.82* 1.38 ns 2.29** 1.93* Slope SD ZMK s Mann Kendall trend test, Slope (Sen s slope) s the change (mm)/annual; **,* s statstcally sgnfcant at 0.05 and 0.1 probabl ty level; ns s non-sgnfcant trend at 0.1; SD s standard devaton; CV s coeffcent of varaton. Table 8. Farmers percepton on the trends and varablty of seasonal and annual ranfall n the study area. Ranfall characterstcs Farmers percepton on ranfall varablty (%) Staton Meteorologcal Increased Decreased No change name trend Annual ranfall NST Kremt ranfall NST Belg ranfall NST Late onset of ranfall Adgrat IST Early cessaton of ranfall NST Length of growng perod DST Number of respondents Annual ranfall NST Kremt ranfall NST Belg ranfall NST Late onset of ranfall Mekelle IST Early cessaton of ranfall IST Length of growng perod DST Number of respondents Annual ranfall NST Kremt ranfall NST Belg ranfall DST Late onset of ranfall Alamata IST Early cessaton of ranfall NST Length of growng perod DST Number of respondents Total N=253; NST s non-sgnfcant trend; DST s decreasng sgnfcant trend and IST s ncreasng sgnfcant trend. ranfall whle 71.3% perceved a declnng trend of belg ranfall totals. Moreover, about 69.5, 67.1 and 70.1% of the contacted farmers at Alamata had perceved a reducng trend of annual, kremt and belg ranfall totals, respectvely. On the other hand, 25% of the farmers at Alamata perceved no change n the annual, kremt and belg ranfall n the last 30 years. Ths result s n lne wth the fndngs of Deressa et al. (2009) and Mengstu (2011) who reported that farmers n northern Ethopa perceved changes n the amount and

12 Academa Journal of Envronmental Scences; Hadgu et al. 170 tmng of precptaton. However, the percepton of farmers that ndcate decreased trend of annual and seasonal ranfall totals dd not agree wth observed meteorologcal data of the area, whch shows non-sgnfcant trend n all statons (Table 8). Ths contradcts the report of Ovuka and Lndqvst (2000). Ths dscrepancy could have evolved due to the fact that ranfall amount receved durng the recent years was below the long term average (Fgure 2). These years are fresh to remember by the farmng communty and hence, nfluence ther percepton. In addton, as mentoned earler, the year to year varablty of the annual and seasonal ranfall s very hgh at all statons studed. Ths could remove the sgnfcant trend n meteorologcal data but leads to recurrent drought and producton loss, whch mght n turn affect the farmers percepton. Smlar to the result of the present study, Meze- Hausken (2004) and Deressa et al. (2009) reported that most farmers notced changes n the amount and occurrence of ranfall n ther localty; yet, the observed clmate data dd not ndcate a sgnfcant trend n Northern Ethopa. Although, most farmers n the regon perceved change n annual and seasonal ranfall totals, there was consderable dfference among the statons. In ths aspect, more than 90% of the farmers at Adgrat had perceved decrease n annual and seasonal ranfall totals whle less than 70% perceved at Alamata. As ndcated n Fgure 2, the relatve frequency of negatve ranfall anomales at Adgrat was hgher than at Alamata and Mekelle. Ths mght be the reason for the dfference n farmers percepton on changes n annual ranfall totals n these statons. Percepton of farmers on trends of onset, cessaton dates and the LGP Farmers n the study area perceved that ranfall events such as onset date, cessaton date and LGP have been changed (Table 8). It ndcated that more than 97% of the farmers at Adgrat had perceved ncreasng late onset and early cessaton of kremt ranfall and consequently, 100% beleved n decreased LGP. Moreover, about 91.5 and 71.8% of farmers at Mekelle had notced an ncrease n frequency of late onset and early cessaton n kremt ranfall, respectvely whle more than 87% perceved decrease n LGP. About 75 and 68% of the contacted farmers at Alamata perceved the ncreased rate of late comng and early wthdrawal of kremt ranfall, respectvely and about 68% of the farmers perceved decreased LGP. The percepton of farmers on kremt ranfall characterstc events such as onset date, cessaton date and LGP has been supported wth observed meteorologcal data of the statons. In ths regard, percepton of farmers on ncrease n frequency of late onset of kremt ranfall and subsequent reducton n LGP agreed wth the observed data at Adgrat, Alamata and Mekelle. However, the percepton of farmers on early wthdrawal of kremt ranfall agreed wth the observed data only at Mekelle. Kemausuor et al. (2011) and Nyanga et al. (2011) reported that farmers n Ghana and Zamba respectvely perceved ranfall tmng had changed, resultng n ncreased frequency of drought. Concluson Detecton of trends usng non-parametrc methods, ncludng Sen's method and the Mann-Kendall test, showed a declne n annual and seasonal ranfall amounts, but these trends were found to be statstcally non-sgnfcant (P>0.05) at most of the statons studed. Ths dsagrees wth the percepton of the local people, whch confrms changes n the form of reducton n annual, kremt and belg ranfall amounts. On the other hand, ranfall events such as onset and cessaton date, length of growng perod and dry spell length have shown sgnfcant trends. Lkewse, the local people also notced an ncrease n the frequency of late onset and early cessaton of the ran and shortenng of the LGP. In concluson, clmate change s apparent n the regon, whch s domnantly expressed n terms of kremt ranfall onset, cessaton date, LGP, dry spell length and number of rany days. Furthermore, most statons were experenced mosture defct and drought condtons n the last decades. If the same trend contnues n the future, more chances of drought are expected. Therefore, some form of copng mechansm both at communty and government levels should be mplemented to reduce the mpact whch mght arse from t. ACKNOWLEDGEMENTS Support for ths study was provded by the Tgray Agrcultural Research Insttute (TARI) and the Ethopan Insttute of Agrcultural Research (EIAR) through the Rural Capacty Buldng Project (RCBP). The authors are also grateful to the Ethopan Natonal Meteorologcal Servce Agency for kndly provdng the daly ranfall data. REFERENCES Araya A, Stroosnjder L (2011). Assessng drought rsk and rrgaton need n northern Ethopa. Agrc. Forest Meteorol. 151: Araya A, Keesstra SD, Stroosnjder L (2010). 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