short rains
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2021 ◽  
Author(s):  
Erik W Kolstad ◽  
David MacLeod

Abstract The East African ‘short rains’ in October–December (OND) exhibit large interannual variability. Drought and flooding are not unusual, and long-range rainfall forecasts can guide planning and preparedness. Although seasonal forecasts based on dynamical models are making inroads, statistical models based on sea surface temperature (SST) precursors are still widely used. It is important to better understand the sources of skill of statistical models and why they sometimes fail. Here, we define a linear regression model, where the August states of El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) predict about 40% of the short rains variability in 1950–2020. The forecast errors are traced back to the initial SSTs: toowet (too-dry) forecasts are linked linearly to positive (negative) initial ENSO and IOD states in August. The link to the initial IOD state is mediated by IOD between August and OND, highlighting a physical mechanism for prediction busts. We also identify asymmetry and nonlinearity: when ENSO and/or the IOD are positive in August, the range and variance of OND forecast errors are larger than when the SST indices are negative. Upfront adjustments of predictions conditional on initial SSTs would have helped in some years with large forecast busts, such as the dry 1987 season during a major El Niño, for which the model erroneously predicts copious rainfall, but it would have exacerbated the forecast performance in the wet 2019 season, when the IOD was strongly positive and the model predicts too-dry conditions.


2021 ◽  
Vol 35 (3) ◽  
pp. 269-275
Author(s):  
Assinapol Ndereyimana ◽  
Bancy Waithila Waweru ◽  
Boniface Kagiraneza ◽  
Arstide Nshuti Niyokuri ◽  
Placide Rukundo ◽  
...  

This study was carried out to determine the effect of vine and fruit pruning on watermelon (Citrullus lanatus) yield. Five pruning methods: P1=no pruning at all, P2=pruning to four vines with two fruits per vine, P3=pruning to four vines with one fruit per vine, P4=pruning to three vines with two fruits per vine and P5=pruning to three vines with one fruit per vine were evaluated on two watermelon cultivars: ‘Sugar baby’ and ‘Julie F1’ under a factorial randomized complete block design with three replications. Investigations were carried out in the seasons 2017A (short rains) and 2017B (long rains) at Karama and Rubona experimental sites belonging to Rwanda Agriculture and Animal Resources Development Board. The obtained results indicated a significant difference among the different cultivars and pruning methods tested during both seasons and at two sites. Generally, all studied parameters recorded higher values during season 2017B than in season 2017A at Rubona site. A similar trend was recorded at Karama site except that the fruit yield per plant and per hectare for plants which were pruned to three vines with one fruit reduced during season 2017B as compared to season 2017A. The highest number of fruits per plant, fruit weight, fruit yield per plant and per hectare was recorded in ‘Julie F1’ compared to ‘Sugar baby’ at both sites and during both seasons. Higher fruit weight was obtained when both cultivars were pruned to three or four vines with one fruit per vine. Higher number of fruits per plant and higher fruit yield per plant was observed under pruning to four vines with two fruits per vine at Rubona site; while at Karama site, higher fruit yield per plant was recorded under pruning to three vines with one fruit or two fruits per vines and pruning to four vines with two fruits per vine. A similar trend was observed in fruit yield per hectare. Based on results of the current study, cultivation of the hybrid ‘Julie F1’ and pruning to three vines with one fruit per vine is recommended for optimum watermelon yield with big-sized fruits.


Author(s):  
Simon Wekesa ◽  
Anne Kelly Kambura ◽  
Marianne Maghenda ◽  
James Gacheru ◽  
John Kimani ◽  
...  

The study evaluated upland rice varietal agronomic characteristics and differences due to effects of fertilizer treatment and season at Taita Taveta University, Ngerenyi campus. The experiment was conducted during the short rains of 2018 and long rains of 2019. The experiment was a Randomized Complete Block Design with 3 replications. Individual plots measured 2.5 m by 2 m. Varieties evaluated were 17KH09010093B, WDR73 Hybrid, NERICA 1, NERICA 10 and Komboka. The treatments included were farm yard manure (8 tons ha-1), DAP at 75 kg ha-1, NPK (17:17:17) at 65 kg ha-1, and no fertilizer. Plant height, panicle length, leaf length, number of tillers, fresh weight, and dry weight were assessed. Variety, fertilizer and season had significant effects (P=0.05) on the morphological variables. NERICA 10 was the tallest variety at a mean of 72 cm in 2018 and a mean height of 61 cm in 2019. DAP treated plants were the tallest in both 2018 and 2019. Varieties were significantly different (P=0.0004) for panicle length. NERICA 10 had the longest panicles. Varietal effect was significant (P<0.001) for leaf length. NERICA 1 had the longest leaves in both seasons. DAP had the greatest effect on leaf length. Varieties differed significantly (P<0.001) in number of tillers per plant. Variety 17KH09010093B had the highest number of tillers per plant of 34.78 obtained in 2018. DAP resulted in the highest number of tillers. Variety and fertilizers interacted significantly (P=0.007) for foliage weight. WDR73 Hybrid out-yielded other varieties (149.31g) in fresh foliage weight. DAP resulted in the highest fresh morphological yield followed by NPK. There were significant differences in dry foliage weight among varieties and between seasons (P<0.001). Variety 17KH09010093B had the highest dry weight. Further studies on the socio–economics of fertilizer use should be conducted to provide reliable recommendations for upland rice production as forage.


Author(s):  
Sharon E. Nicholson ◽  
Douglas Klotter ◽  
Adam T. Hartman

AbstractThis article examined rainfall enhancement over Lake Victoria. Estimates of over-lake rainfall were compared with rainfall in the surrounding lake catchment. Four satellite products were initially tested against estimates based on gauges or water balance models. These included TRMM 3B43, IMERG V06 Final Run (IMERG-F), CHIRPS2, and PERSIANN-CDR. There was agreement among the satellite products for catchment rainfall but a large disparity among them for over-lake rainfall. IMERG-F was clearly an outlier, exceeding the estimate from TRMM 3B43 by 36%. The overestimation by IMERG-F was likely related to passive microwave assessments of strong convection, such as prevails over Lake Victoria. Overall, TRMM 3B43 showed the best agreement with the "ground truth" and was used in further analyses. Over-lake rainfall was found to be enhanced compared to catchment rainfall in all months. During the March-to-May long rains the enhancement varied between 40% and 50%. During the October-to-December short rains the enhancement varied between 33% and 44%. Even during the two dry seasons the enhancement was at least 20% and over 50% in some months. While the magnitude of enhancement varied from month to month, the seasonal cycle was essentially the same for over-lake and catchment rainfall, suggesting that the dominant influence on over-lake rainfall is the large-scale environment. The association with Mesoscale Convective Systems (MCSs) was also evaluated. The similarity of the spatial patterns of rainfall and MCS count each month suggested that these produced a major share of rainfall over the lake. Similarity in interannual variability further supported this conclusion.


2021 ◽  
Author(s):  
Athanase Nkunzimana ◽  
Bi Shuoben ◽  
Wang Guojie ◽  
Ahmed Alriah Mohamed Abdallah ◽  
Isaac Sarfo ◽  
...  

Abstract This study assessed the drought events across Burundi for 37 years ranging from 1981 to 2017. The drought assessment was conducted using the Standardized Precipitation Index (SPI) at 1, 3, 6 and 12-month time scales. The Mann Kendall and Modified Mann Kendall trend tests and Sen’s slope statistic tests were used to analyse the spatiotemporal drought trend. The overall analysis of SPI-3, SPI-6 and SPI-12 outputs revealed that the Northern part of Burundi was the most threatened by dry events, and more than 80% of the extremely and severely dry events occurred within the period 1993–2000. The drought magnitude varied highly in the short rains season (SOND) than during the long rains season (MAM) specifically during the 1990s decade. The cumulative frequency of extremely dry events was very high in the North with 5.2%, 6.1% and 7.4 % at 3, 6 and 12-month time scales respectively. Likewise, the northern part experienced both short, medium and long dry periods, thus 88 consecutive dry months within only 8 years. The North and East regions exhibited a positive increasing trend over annual and seasonal time scales at both 3, 6, and 12 months of SPI analysis while the mountainous region and the South experienced a significant decreasing trend. The first abrupt point issued by forward and backward sequential statistics occurred in 1990, the year corresponding to the beginning of the driest period. Dry years are associated with circulation anomalies over the Indian Ocean and La Nina events.


2021 ◽  
Author(s):  
Markus Adloff ◽  
Michael Bliss Singer ◽  
David McLeod ◽  
Katerina Michaelides ◽  
Nooshin Mehrnegar ◽  
...  

&lt;p&gt;Rural communities in the Horn of Africa Drylands (HAD) rely on the availability of soil moisture for crop growth and groundwater for drinking water supply for people and livestock. Recent negative trends in March-May rainfall (&amp;#8216;long rains&amp;#8217;) have decreased soil moisture with negative consequences for the livelihoods in HAD communities, who have become increasingly vulnerable to multi-season droughts affecting crops and livestock. These increasingly common failed &amp;#8216;long rains&amp;#8217;, propagate into agricultural drought, causing famines, and lead to major humanitarian intervention across HAD. However, the links between seasonal rainfall (&amp;#8216;long rains&amp;#8217; and &amp;#8216;short rains&amp;#8217; in October-December) and regional groundwater storage in HAD have not been explored. We examined trends in seasonal rainfall from various gridded datasets alongside an analysis of total water storage (TWS) from GRACE satellite data. Multiple rainfall datasets corroborate declining &amp;#8216;long rains&amp;#8217; and increasing &amp;#8216;short rains&amp;#8217;, and a 3-hr (MSWEP) dataset reveals the disproportionate contribution of extreme rainfall to totals within both seasons. We also found that TWS generally increased across the HAD region between 2002 and 2017, and that the GRACE TWS signal is primarily composed of groundwater storage changes for this region, rather than trends in soil moisture. We then found that groundwater storage variability correlates strongly with seasonal rainfall on interannual and decadal scales, and it is particularly correlated with extreme rainfall in both rainy seasons. We highlight the importance of increasingly large Indian Ocean Dipole events in dominating extreme rainfall and correspondingly high TWS and groundwater recharge within the October-December rainy season. While groundwater recharge in HAD by high-intensity rainfall is generally high for the March-May rainy season, it is increasing for the &amp;#8216;short rains&amp;#8217; season. These findings raise the possibility that increasing groundwater availability across HAD could be exploited to offset the &amp;#8216;long rains&amp;#8217; decline, potentially mitigating their climate change impacts on soil moisture, crops, and drinking water supplies.&lt;/p&gt;


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