| dc.description.abstract | This study examined the space-time characteristics of minimum and maximum
temperature values over the Tropical Eastern Africa region in order to delineate any
significant changes in the traditional space-time temperature characteristics over the
region. The temporal characteristics investigated in the study included the inter-annual
patterns of the trend, seasonal and cyclical variations at the individual stations.
Both graphical and statistical methods were used in the trend analysis. In the
graphical approach, visual examination of the inter-annual trend was used whilst analysis
of variance (ANOVA) and non-parametric methods were used in the statistical
approach. The recurrences of low/high inter-annual temperature values were examined
using the maximum entropy method (MEM) of spectral analysis.
The last part of the study attempted to provide some insight into the potential
causes of the observed inter-annual variability in the temperature characteristics. EINino/
Southern oscillation (ENSO), the Quasi-Biennial Oscillation (QBO), cloudiness,
and OLR data were used in the study to quantify the regional/global scale systems that
may be associated with the observed temperature characteristics. Relationships between
these systems and the observed temperature characteristics were investigated using
Simple correlation analysis. X2 -tests were used in case of grouped minimum and
maximum temperature observations.
The data used in the study was from 53 stations with record lengths of 24 and
53 years. All the data were quality-controlled before they were used in any analysis.
Results of the quality-control analysis declared most of the temperature records within
Tropical Eastern Africa to be homogeneous as most of the mass curves were linear.
Instrumental records world-wide have been affected by changes in instrument types,
changes in observational schedules and methods, and changes m the station
environment.
The inter-annual minimum and maximum temperature patterns showed distinct
decadal variability signals in the observed minimum and maximum temperature records.
The 1980's decade was generally the warmest in record at most of the locations. The
late 1970's and the early 1990's were also relatively warm periods in most areas. These
patterns were however reversed at maritime and lake areas.
The warming/cooling observed at some locations m recent years introduced
significant linear trends when the records were subjected to trend analysis. The
observed minimum and maximum temperature trend patterns however showed a lot of
geographical and seasonal variations. Some locations did not indicate any significant
trend signals.
Recurrences of extremely high/low values were the commonest feature of the
inter-annual variability patterns of the minimum and temperature records. Results of the
spectral analysis showed recurrences of extremely high/low temperature values centred
around four major spectral peaks namely, 2-29 years, 3-4 years, 4.5-6.5 years, and 10-
12.5 years. Few spectral peaks also appeared with longer periods of recurrence. The
long-period cycles were however not statistically significant at most of the locations.
The 2-2.9 years spectral peak was associated with the QBO whilst the 3-4 and
4.5-6.5 years peaks were associated with the inter-annual variability in ENSO
characteristics. The 10-12.5 years cycle was associated with the solar variability cycle.
These quasi-periodic oscillations have also been observed in many other Climatic
parameters over the region They however explained a very small proportion of the
total inter-annual temperature variation.
Results of the Simple correlation analysis indicated that both morning and
afternoon cloudiness were negatively correlated with the observed minimum and
maximum temperature values and the subsequent temperature range. Maximum
temperature values were also found to be significantly correlated with QBO phases.
Statistically significant correlations were also found between the minimum and
maximum temperature values and the Southern Oscillation Index (SOl), especially for
time-lagged temperature values.
It may be concluded from this study that the period starting from the 1970's to
the early 1990' s was relatively warm at a number of locations in the study region.
Relative cooling or no temperature change at all was observed at most maritime
locations within the same period. Large variations were however evident in the spacetime
characteristics of the warming/cooling trends. The observed warming/cooling
trends may have been reflective of inter-decadal temperature variability. To determine
whether these trends were actually signals of new inter-decadal variability in the
minimum and maximum temperature records, the temperature observations of the
1990's will be central. Although no comprehensive analysis was carried out to delineate
urbanisation effects in the study, preliminary examination showed that a larger scale
phenomenon may be responsible for the observed minimum and maximum temperature
trends. A more elaborate study will however be required to delineate with certainty the
role played by urbanisation in the observed warming/cooling signals.
The findings of this study are of utmost importance especially at this time when
much political, scientific, and socio-economic attention has been focused on human-induced
Climate issues. Temperature is an important parameter in the determination of
the space-time distribution of natural resources, and life in general. These findings will
therefore be useful to planners and managers of food, agriculture, water, socioeconomic,
and many other natural resources that are Climate-dependent. The findings
will complement the current global search for models that can incorporate climate
change and variability at the regional and local levels. | en |
