BY:REGINAH QUEEN MANYATHELO 25-09-2017
Introduction: Botswana rainfall pattern is highly influenced by the position of the Inter Tropical Convergence Zone (ITCZ). Its movement and intensity determines the intensity of the seasonal rainfall, particularly from January March. also r/fall is indirectly influenced by the position of TCs in the SWIO and the passage of Easterly waves. dry conditions are occasionally experienced in association with such weather systems. The mid-level westerly waves moving over the country may create an unstable environment conducive to rainfall. The strength of the sub-tropical high pressure belt determines the lowlevel influx of tropical moisture into the country. Normally, during summer (October to February), extremely high temps are experienced over the country with frequent dry spells and heat waves causing a lot of evaporation and heat stresses. Concurrently, Botswana is highly dependent on the rain-fed subsistence agriculture, and its rainfall pattern is very erratic, hence continuous monitoring and early warning is vital for maximizing agricultural produce and disaster preparedness.
RAINFAL_-Month of October 2015 The season of 2015/2016 begins born dry, October 2015 received minimal rainfall. The highest rainfall (103.6mm on...) was recorded at Selibe- Phikwe synoptic station in the Central part. The rest of the country has >35.0mm or little/no rain. Daily maximum temperatures were above averages at all stations;(38 ⁰C and 40 ⁰C) were recorded in the northern parts of the country: Kasane 39.9; Sowa Town 39.5⁰C, Maun 39.2⁰C, Francistown& Letlhakane 39.0 ⁰C; Mahalapye 38.9⁰C. & Werda 39.9⁰C in the west. Graph : Shows the Maximum temperatures for the Month of October 2015
Figure : Total Rainfall for Oct 2015 Figure : Departure from Normal for Oct 2015 RAINFALL SITUATION - OCTOBER 2015:
NOVEMBER 2015 RAINFALL SITIUATION: In Novembe r 2015 very high temperatures continued with characteristic of stormy destructive rains; which caused damage to human property, including loss of livestock and horticultural produce. E.g. on19th November 2015 in the afternoon at around 1330hrs,severe hailstorm with heavy rains was experienced at Mathangwane village (see figure1(a) ; which is 30km to the northwest of the city of Francistown which is in the north-eastern part of Botswana. The synoptic features prevailing was a Very low pressure (475 to 458mb) at the surface; at 700mb medium level ; there was a secondary westerly trough which caused instability at the medium levels ; and there was a very dense clouds around that(of N/Eastern parts of Botswana) area.
Rainfall of 82.3 mm was recorded at Mathangwane Agricultural Research station on the 19 th Nov. The hail accumulated was about half a meter deep from the ground.(see fig 1(a)and fig 1(b) houses unroofed].
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Daily Maximum temps were well above the long term average, with daily extreme maximum temperatures ranging between 39ºC - 42ºC occurred during the second week the month. Francistown reached 41.5 C and 41.6ºC on two consecutive days (11th and 12th) and exceeded the highest ever recorded over that area,( See Graph1 below).
Temperature(ºC)e 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 Mean max Highest max Maximum Temperature for December 2015 Goo Letlh F/To Mau Shak Gha Tsab Tsha Kasa Jwan S.S.K Mah Leph Sow Pand d akan wn n awe nzi ong ne ne eng.a alap epe a a Hop e e Sele Wer bi da Phik we 34.9 35.3 35.4 35.2 37.4 36.1 32.7 35.5 35.7 35.0 35.7 36.4 35.5 33.3 34.3 37.7 35.3 40.2 38.5 40.2 39.2 41.8 39.3 34.9 39.4 40.2 39.9 38.9 40.4 39.2 37.2 38.6 41.9 39.7 LTM 31.0 32.9 32.4 33.3 34.4 33.8 31.1 31.9 31.8 31.3 30.3 31.6
Rainfall Accumulation(Oct. to Dec 2015, Fig1 below): shows Below normal rains still continued as attributed to Elno event. The first half of the rainfall season(october to December 2015) had experienced much below normal rainfall. The distribution for the period October to December 2015 was poor in both space and time. Much of rainfall was confined to the eastern parts(fig 1below).
Reports had shown that January was the hottest month on record during the 2015/2016. Extremely High temperatures continued observed throughout the month over the entire country. Daily Maximum temps were well above the long term averages. ( Temp-Graph ). Table(Jan2016) of Extrem. Daily Temps against previous records. RAINFALL IN JANUARY2016 The month of January experienced some moderate rains of more than 100mm in the second week over Ngamiland, Gantsi and parts of Kweneng districts recorded more than 60mm for the month.. Rainfall was low inchobe, Gantsi, N-Ngamiland, Kweneng; Northeast Districts. (Refer Figure 1) On avegin Jan2016, rainfall was still below normal despite some moderate rains over the north. Much below normal rains occurred over the south.
Figure : Accumulated rainfall for January 2016 in mm Figure : Departure from normal for January 2016
TEMP-Graph : Maximum temperatures for January 2016
Drought in Ngamiland: 15000 cattle already dead due to devastating drought (Mmegi newspaper) January 2016.
Month of FEBRUARY 2016: February _floods
A Cemetery in Ramotswa village(se) flooded 13 th Feb. 2016
Nb: rainfall season. RAINFALL SITUATION- Feb Accumulated Rainfall For February 2016 In Mm The eastern parts of the country received moderate to heavy rainfall ranging between 50.0 mm and 200.0 mm. the highest rainfall amounts were recorded over most parts of the central, chobe and northeast parts of the country.
Figure : RAINFALL SITUATION-FEB2016 The eastern parts of the country received moderate to heavy rainfall ranging between 50.0 mm and 200.0 mm. The highest rainfall amounts were recorded over most parts of the Central, Chobe and Northeast.
The good rains that occurred in February 2016 had improved Hydrological status in terms of recharging dams and rivers; Water availability for livestock; Malaria cases ; Temperatures had declined/decreasesd significantly due the weakening of the El-NINO status. In Feb, daily max temperatures have been well above normal over the entire country but lower than those of January. Extremes of 40⁰C were recorded in Gantsi, Mahalapye, Sir Seretse Khama Inter.Airport, &Tsabong.
250 Rainfall total (mm) for March 2016 & Longterm average 200 rainfall (>50mm) 150 100 50 0 Rainfall (> 50mm) LTM (1971-2000)
Month of March 2016;ITCZ moved down into the country and it was responsible for heavy rains which occurred during 1 st and 2 nd week parts of the country (Fig 1). The distribution of this rains was good in area coverage but temporaly fair because the rains declined in the third week. MAXIMUM TEMP FOR MARCH 2016 Temperature( C) 40.0 30.0 20.0 10.0 0.0 GANTS I SHAKA WE KASAN E MAUN FTOW N MAHAL APYE TSHAN E JWANE NG SSKA TSABO NG LETLH AKANE PANDA Highest max temp 34.5 33.69 32.6 36.3 33.4 32.7 35.4 35.5 34.4 36.7 36.0 33.1 Monthly mean temp 31.1 31.1 29.6 33.1 30.5 29.2 31.3 30.2 30.3 32.7 32.3 29.6 Long term average 31.1 30.8 30.9 31.9 30.1 29.7 31.3 29.9 30.2 31.9 31.0 30.1
SEASONAL RAINFALL SUMMARY ( OCTOBER 2015 TO MARCH 2016)
SUMMARY(of the Rainfall season 2015/2016 ) The whole season(2015/2016) was poor in both space and time. Although there was some significant rains in February and March 2016, the season performed poorly. The country was characterised by much below normal to normal rains. The late rains increased water levels in dams, water for animals and improve vegetation condition.
RAINFALL SEASON 2016/2017 MONTHLY SITUATIONS : OCTOBER 2016 In October 2016, Botswana continued to be hotter than the average conditions as reflected by all the stations in the graph below. Gantsi, Shakawe, Tsabong and Tshane recorded extremely hot temperatures of 41.4 0 C, 41.6 0 C, 40.7 0 C and 41.0 0 C respectively(see below).
November was hotter than normal, across the whole country. Tsabong recorded the highest temperature of 44.0 0 C on the 1 st followed by Werda at 41.0 0 C and Ghanzi at 40.4 0 C on the same day. So the 1 st of November was the hottest day of the month
During the month of November 2016, the Central District received a significant amount of rainfall; in which Orapa Police Station recorded an amount of 121.5mm on the 19th of November 2016. Motshegaletau Primary School on the other hand received the highest total rainfall of 213.9mm during this month.( Fig ) Most places recorded below normal rains except for three pockets with above normal rains.
DECEMBER 2016 Temperatures
RAINFALL SITUATION _DEC 2016: During the month of December 2016, much of the rainfall was confined to the northern parts of the Central district and Chobe; where a cumulative rainfall amounts of more than 200.0mm was recorded over the Northern Central. Nata vllge recorded the highest cumulated rainfall of 218.0mm, followed by Mmashoro with 171.0mm
RAINFALL SITUATION: OCTOBER TO DECMBER 2016: For the Season of October to December 2016, It is notable that indeed the Eastern half of the country had received more rainfall as compared to the Western parts.
RAINFALL SITUATION_JANUARY 2017 The month of January 2017 received above normal rainfall in many if not all parts of Botswana; that was due to weather systems, that included an easterly wave at upper levels (500mb), a low pressure at the surface (850mb) and negative vorticity (instability) in the atmosphere. Heavy rains were experienced in many places resulting in floods as well as damage to infrastructure and property and general inconvenience to people s daily activities. The Metsimotlhabe and Moshupa villages (in SE)floods were a few examples.
Fig : Cumulative rainfall for January 2017 :(shows that CKGR received the highest amounts of rainfall).
Fig : % departure from normal for January 2017 Fig shows that Rainfall was much above normal over the south (purple and blue) whilst being largely normal over the north (green).
Graph : Mean Maximum temperatures for January 2017 Mean monthly maximum temperatures were cooler than long-term average temperatures. This is because the month of January had significantly good rains and it was characterised by cloudy days which had the effect of cooling temperatures.
Cumulative rainfall for February 2017. RAINFALL SITUATION AND FLOODS _ MONTH OF FEBRUARY 2017 Generally normal to much above normal rainfall were received over most parts of the country during February 2017.
February like January was cooler than normal. The entire country enjoyed cooler temperatures mainly because of the rainfall received in February. Tsabong had the highest average maximum temperature of 30.5⁰C followed by Werda and Kasane with 30⁰C each
FLOODS IN FEBRUARY 2017 The month of February 2017 received normal to above normal rainfall almost over the entire country. Cumulative rainfall amounts of above 80mm were reported over Chobe, Ngamiland, Central, Kweneng, South East, Southern Districts and the southern parts of Gantsi. Rainfall less than 80mm was recorded over Kgalagadi, Bobirwa, northern and western parts of Gantsi and Ngamiland. The predominant phenomenon which influenced rainfall over Botswana was the effects of Tropical Cyclone Dineo, which by the time it reached Botswana on the 17th February; it was already downgraded to a Tropical Low., moved across northern Botswana into Ghanzi District and was absorbed into the westerlies, subsequently moving across southern Botswana by the 19th. This resulted in heavy downpours including over the Gaborone Dam catchment area. Gaborone Dam was filled to capacity for the first time in 16 years. On the 21st February, Sunnyside Ranch near Lobatse recorded 204.0mm in 24 hours. Flooding was experienced in many areas causing a lot of damage to infrastructure, property and general inconveniences to peoples livelihoods.
Wed 15 Feb 2017, 12:38 pm (GMT +2) (Mmegi News Paper ) GABORONE DAM(100% FULL) OVERFLOWS_FEBRUARY2017 (DAM IN THE CAPITAL CITY OF BOTSWANA) Ironically Gaborone Dam was declared officially dry in 2016(previous season) around the same month of february. Accroding to WUC s spokesperson, 2015 was the worst year on dam levels records since it was commissioned. By February 2015, only 1.3 per cent was left of the dam with a carrying capacity of 141.4 million cubic metres which loosely translates to over 141 billion litres of water. Technically a dam fails at five per cent capacity. Back in the years between 1981 and 1985 severe droughts were experienced in the south resulting in the raising of the dam wall. In 2000, an over spill was recorded and the period between 2000 and 2006 resulted in levels dropping to 16 per cent. The last full capacity record was in 2007. On Saturday afternoon, hope was finally restored to many Batswana after the majestic dam finally hit the 100 per cent mark. The good news was all dams up north that feed into the NSC pipeline are all above their full capacities. However, while the rain has been a blessing, WUC has urged communities living within the vicinity of the dam to be on high alert as disaster management teams remain on standby. Only roads and property were reportedly swept away by heavy rains of mid-february2017.
FLOODS IN BOTSWANA DURING FEBRUARY 2017 - Pic: Gaborone Dam- February 2017.
Floods Wreak Havoc In Botswana Staff Reporter Feb 27, 2017
Other effects of FLOODS TO BOTSWANA: A bridge that links Lobatse with Gaborone also collapsed while Ramotswe village, about 30 kilometres from Gaborone, was submerged. Roads linking major settlements to the capital were closed and the department of roads advised the public across the country to cancel trips as other bridges continued to collapse. The heavy rains, which affected most parts of the country, also led to the temporary closure of some border posts linking Botswana with South Africa. Minister of Transport and Communications Kitso Mokaila described the situation as a catastrophe. This is not only destruction to government s assets but a tragedy. Cyclone Dineo leaves P572 Billion for roads The downpours flooded most areas in Botswana destroying public infrastructure, homes and fields while leaving thousands of families in dire straits. At the Public Accounts Committee (PAC) yesterday, Ministry of Transport and Communications permanent secretary- Kabelo Ebineng said a budget of P572m had been reserved to repair roads damaged by the tropical cyclone.
RAINFALL SITUATION _ MONTH OF MARCH 2017. For most of March 2017 a dry spell was experienced over of the country. The first week received most of the rainfall but the 2nd and 3rd weeks were mostly dry. Generally rainfall was much below normal for March 2017, except over the extreme north
Graph : Maximum temperatures for March 2017 For maximum temperatures, monthly means were generally cooler than expected except at Tsabong and Werda which were warmer than normal (see graph below). Tsabong had the highest monthly mean of 32.4 C followed by Werda with 32.2 C.
Gaborone : Floods caused destruction in Botswana as bridges collapsed while roads and railway lines were washed away. A goods train belonging to Botswana Railways that was travelling from Mafikeng in South Africa derailed in Lobatse, about 70 kilometres from Gaborone, because of the floods caused by Cyclone Dineo which hit most parts of Mozambique and South Africa. A bridge that links Lobatse with Gaborone also collapsed while Ramotswe village, about 30 kilometres from Gaborone, was submerged. Roads linking major settlements to the capital were closed and the department of roads advised the public across the country to cancel trips as other bridges continued to collapse. The heavy rains, which affected most parts of the country, also led to the temporary closure of some border posts linking Botswana with South Africa. Minister of Transport and Communications Kitso Mokaila described the situation as a catastrophe. This is not only destruction to government s assets but a tragedy.
Seasonal Rainfall summary: OCTOBER 2016 TO MARCH 2017 RAINFALL Fig : Cumulative rainfall for October 2016 to March 2017
Fig(Seasonal r/fall summary2016/2017: shows cumulative rainfall for the rainfall season October 2016 to March 2017. Rainfall amounts of between 200.0mm and 800.0mm were received over the country. Baipidi Primary School (Makalamabedi) in the northerncentral had the highest rainfall of 803.1mm for the season followed by Ramogotsi Primary School (Morwa) in kgatleng district and Sua CJSS (N-central) at 802.0mm and 720.4mm respectively. It should be noted that the season(2016/2017) the effects of Tropical cyclone Dineo played a significant role in the rains received and caused havoc to Botswana like TC Eline in 2000.
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