scholarly journals Spatial and temporal analysis of the mid-summer dry spells for the summer rainfall region of South Africa

Water SA ◽  
2021 ◽  
Vol 47 (1 January) ◽  
Author(s):  
MG Mengistu ◽  
C Olivier ◽  
JO Botai ◽  
AM Adeola ◽  
S Daniel
Keyword(s):  
South Africa ◽  
Markov Chain ◽  
Crop Yields ◽  
Summer Rainfall ◽  
Seasonal Rainfall ◽  
Chain Model ◽  
Summer Period ◽  
Dry Spells ◽  
Dry Spell ◽  
Rainfall Region

South Africa is frequently subjected to severe droughts and dry spells during the rainy season. As such, rainfall is one of the most significant factors limiting dryland crop production in South Africa. The mid-summer period is particularly important for agriculture since a lack of rain during this period negatively affects crop yields. Dry spell frequency analyses are used to investigate the impacts of sub-seasonal rainfall variability on crop yield, since seasonal rainfall totals alone do not explain the relationship between rainfall and crop yields. This study investigated the spatial and temporal occurrences of the mid-summer dry spells based on magnitude, length and time of occurrence in the major maize growing areas of the summer rainfall region of South Africa. Three thresholds of 5 mm, 10 mm, and 15 mm total rainfall for a pentad were used for the analysis of dry spells.  Dry spell analysis showed that dry pentads occur during mid-summer with differing intensity, duration and frequency across the summer rainfall region. Annual frequency of dry pentads for the mid-summer period ranged between 0 and 4 pentads for the 5 mm threshold and 1 to 7 for the 10 mm and 15 mm thresholds.  The non-parametric Mann-Kendall trend analysis of the dry pentads indicates that there is no significant trend in the frequency of dry spells at a 95% confidence level. The initial and conditional probabilities of getting a dry spell using the Markov chain model also showed that there is a 32% to 80% probability that a single pentad will be dry using the 15 mm threshold. There is a 5% to 48% probability of experiencing two consecutive dry pentads and 1% to 29% probability of getting three consecutive dry pentads. The duration and intensity of dry spells, as well as the Markov chain probabilities, showed a decrease in dry spells from west to east of the maize-growing areas of the summer rainfall region of South Africa.

scholarly journals Spatial and Temporal Analysis of Dry and Wet Spells in Upper Awash River Basin, Ethiopia

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3051
Author(s):  
Girma Berhe Adane ◽  
Birtukan Abebe Hirpa ◽  
Chul-Hee Lim ◽  
Woo-Kyun Lee
Keyword(s):  
River Basin ◽  
Management Practices ◽  
Markov Chain Model ◽  
Temporal Analysis ◽  
Chain Model ◽  
Rainfall Analysis ◽  
Dry Spells ◽  
Dry Spell ◽  
Awash River Basin ◽  
Wet Spells

This study aimed to analyze the probability of the occurrence of dry/wet spell rainfall using the Markov chain model in the Upper Awash River Basin, Ethiopia. The rainfall analysis was conducted in the short rainy (Belg) and long rainy (Kiremt) seasons on a dekadal (10–day) scale over a 30-year period. In the Belg season, continuous, three-dekad dry spells were prevalent at all stations. Persistent dry spells might result in meteorological, hydrological, and socio-economic drought (in that order) and merge with the Kiremt season. The consecutive wet dekads of the Kiremt season indicate a higher probability of wet dekads at all stations, except Metehara. This station experienced a short duration (dekads 20–23) of wet spells, in which precipitation is more than 50% likely. Nevertheless, surplus rainwater may be recorded at Debrezeit and Wonji only in the Kiremt season because of a higher probability of wet spells in most dekads (dekads 19–24). At these stations, rainfall can be harvested for better water management practices to supply irrigation during the dry season, to conserve moisture, and to reduce erosion. This reduces the vulnerability of the farmers around the river basin, particularly in areas where dry spell dekads are dominant.

scholarly journals Downscaling summer rainfall in the UK from North Atlantic ocean temperatures

2001 ◽  
Vol 5 (2) ◽  
pp. 245-257 ◽  
Author(s):  
R. L. Wilby
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Summer Rainfall ◽  
Model Parameters ◽  
Rainfall Forecasting ◽  
Dry Spells ◽  
Dry Spell ◽  
The Uk ◽  
Sst Anomalies

Abstract. Annual series of three stochastic rainfall model parameters — the seasonal wet day amount (or intensity), the conditional dry–day probability (or dry–spell persistence), and the conditional wet-day probability (or wet-spell persistence) — were examined using daily rainfall records for ten UK stations for the period 1901–1995. The purpose was first, to determine the extent to which these indices of summer (June–August) rainfall were correlated with empirical orthogonal functions (EOFs) of summer North Atlantic sea surface temperature (SST) anomalies: second, to evaluate the skill of EOFs of preceding winter (December–February) SSTs for summer rainfall forecasting and downscaling.Correlation analyses suggest that observed increases in summer dry-spell persistence since the 1970s coincided with positive SST anomalies in the North Atlantic. In contrast, wet-spell persistence and intensities were relatively weakly correlated with the same patterns, implying that the use of SSTs is justifiable for conditioning occurrence but not intensity parameters. Furthermore, the correlation strengths were greater for EOFs of SSTs than those reported for area-average SST anomalies, indicating that the pattern of SST anomalies conveys important information about seasonal rainfall anomalies across the UK. When EOFs of winter SSTs were used to forecast summer rainfall in Cambridge, the skill was once again greater for dry-spells than either wet-spells or intensities. However, even for dry–spells, the correlation with observations — whilst statistically significant — was still rather modest (r<0.4). Nonetheless, the results are comparable to previous investigations of summer rainfall across Europe, and suggest that forecasting skill (across the UK) originates from the predictability of the rainfall occurrence process. Keywords: North Atlantic, ocean temperatures, downscaling, rainfall, forecasting, UK

scholarly journals Geographical Variability of Drought in Northern South Africa

2017 ◽  
Vol 9 (1) ◽  
pp. 53
Author(s):  
Tibangayuka A Kabanda
Keyword(s):  
South Africa ◽  
Seasonal Rainfall ◽  
Dense Network ◽  
Rainfall Characteristics ◽  
Rainfall Season ◽  
Geographical Variability ◽  
Dry Spells ◽  
Source Data ◽  
Precipitation Indices ◽  
Drought Occurrence

This study focuses on the geographical variation of drought in northern South Africa (hereafter NSA). It assesses seasonal rainfall characteristics to determine drought occurrence and persistence in NSA. Seasonal rainfall data for the period 1960-2009 is used and was obtained from the South Africa Weather Service (SAWS). Rainfall stations in NSA are well distributed, forming a dense network of point-source data samples. Standardised Precipitation Indices (SPIs) are employed to detect drought occurrence and intensity at different locations. Analysis of SPIs with respect to time suggests that the severity of drought results from the accumulation of consecutive dry spells within a rainfall season and sometimes even consecutive dry rainfall seasons. It also shows the intensity and frequency of drought has increased in recent years.  The trend towards worsening drought conditions has significant socioeconomic implications for the region and other areas with similar geographical settings.

Late Holocene precipitation variability in the summer rainfall region of South Africa

2013 ◽  
Vol 67 ◽  
pp. 105-120 ◽  
Author(s):  
J. Curt Stager ◽  
David B. Ryves ◽  
Christiaan King ◽  
Jerome Madson ◽  
Matthew Hazzard ◽  
...  
Keyword(s):  
South Africa ◽  
Late Holocene ◽  
Summer Rainfall ◽  
Precipitation Variability ◽  
Rainfall Region

Dry Spells Occurrence in Tamale, Northern Ghana – Review of Available Information

2014 ◽  
Vol 9 (4) ◽  
pp. 468-474 ◽  
Author(s):  
Gordana Kranjac-Berisavljevic ◽  
◽  
Shayibu Abdul-Ghanyu ◽  
Bizoola Zinzoola Gandaa ◽  
Felix K. Abagale
Keyword(s):  
Crop Production ◽  
Crop Yields ◽  
Daily Rainfall ◽  
Northern Ghana ◽  
Growth Stages ◽  
African Region ◽  
Rainfed Rice ◽  
Dry Spells ◽  
Rain Season ◽  
Dry Spell

Sustainable crop production is important for food security in Northern Ghana, where highly variable rainfall coupled with high evaporation rates and soils prone to degradation combine to produce low crop yields of main staple crops that are vital for local people’s livelihoods. Rainfall in this region generally ranges between 800 mm and 1200 mm per annum, falling within a single rainy season from April to October, with a peak in late August-September. This amount is adequate for most arable crops such as maize, rainfed rice, soybeans, and yams. Intermittent dry spells occur, however, at critical crop growth stages, resulting in significant yield reductions. Several studies conducted in this area show that dry spells can be expected during each annual rain season, with a high level of certainty and duration fromtwo to three days up to four weeks. This paper reviews both available literature on dry spell incidence and rainfall prediction in the West African region, with a particular focus on northern Ghana. Available daily rainfall data for 52 consecutive years are analyzed to determine dry spell duration and occurrence in northern Ghana.

Sign in / Sign up

Export Citation Format

Share Document