The 15-year span from 1960 to 1975 is a key period in Tanzania’s climate history. Analyzing the weather data establishes a baseline for understanding long-term shifts. This era exhibited a complex mix of subtle warming trends and highly disruptive rainfall anomalies that set the stage for later environmental challenges. The meteorological record reveals a climate system already showing signs of instability, particularly concerning water availability.
Setting the Climate Context
Tanzania’s climate is governed largely by the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ), a belt of low pressure near the equator that brings moisture. This circulation pattern creates two primary rainfall regimes across the country, influencing both agricultural practices and natural ecosystems. The northern and coastal regions experience a bimodal pattern, defined by two distinct rainy seasons each year.
These seasons are locally known as the Vuli (short rains), typically occurring from October to December, and the Masika (long rains), which fall between March and May. Conversely, the central, southern, and western parts of the country follow a unimodal pattern, receiving most of their annual rainfall in a single, prolonged season that usually lasts from December to April.
Documented Temperature Shifts
Temperature records spanning 1960 to 1975 indicate the territory was entering a warming phase, though the change was not uniform across all metrics. Studies analyzing the broader region show that mean annual temperatures have increased since 1960, with an average warming rate of approximately \(0.23^\circ C\) per decade. However, the early part of this era, particularly the 1960s, was characterized by some of the lowest recorded maximum temperatures within the long-term meteorological datasets.
This suggests that while the overall upward trend was beginning, the climate was not experiencing extreme daytime heat compared to later decades. The warming signal was more pronounced in the nighttime minimum temperatures, a common indicator of atmospheric change. Across the country, the frequency of cold nights began to decrease significantly during this time, even in the higher altitude areas.
The observed temperature anomalies were often negative, or cooler than a later reference period, such as in the Arusha region (1961 and 1981). This early shift toward a reduced number of cold nights, combined with less dramatic changes in maximum daytime temperatures, points to a subtle yet definite alteration in the thermal environment. The increase in minimum temperatures is often linked to increased atmospheric moisture, which traps heat more effectively overnight.
Variability in Precipitation Patterns
Rainfall variability proved to be the most impactful climatic feature of the 1960–1975 period, directly affecting the country’s predominantly rain-fed agricultural systems. Long-term data for Tanzania reveals a general decreasing trend in annual precipitation since 1960, with the southern regions showing the most substantial reductions. This era was marked by increasingly erratic and diminished rainfall, contrasting sharply with the expected reliability of the seasonal systems.
In the bimodal rainfall zones along the coast, the Masika (long rains) season showed a distinct trend toward decreased rainfall totals. This reduction in the most reliable agricultural season created significant stress on farming communities. Meanwhile, the Vuli (short rains) season exhibited a highly periodic pattern, with its success or failure often linked to the strong influence of the El Niño-Southern Oscillation (ENSO) phenomenon.
The instability of these seasonal rains made agricultural planning increasingly difficult. Historical accounts described altered rainfall patterns, characterized by a failure of expected seasonal rains or a poor distribution of precipitation during wet months. This instability foreshadowed the more pronounced drought cycles that would affect the region in subsequent decades.
Notable Extreme Weather Events (1960-1975)
The 15-year period was bookended by two acute and historically significant weather anomalies. The first major event was the extreme rainfall and flooding toward the end of 1961, which affected a large portion of East Africa. This caused widespread flooding and a rapid, sustained rise in the levels of major water bodies, including Lake Victoria.
This intense flooding episode was followed by the most severe weather event: the devastating 1973–1974 drought. This multi-year drought caused catastrophic food shortages across Tanzania, compelling the government to use scarce foreign exchange reserves to import emergency food supplies. This crisis led to the launch of a national “Do or Die Cultivation Campaign” in 1975 to address the agricultural collapse.
The contrast between the 1961 extreme wetness and the 1973–1974 severe dryness highlights the growing volatility of the Tanzanian climate system. These two events demonstrated the system’s capacity for both destructive abundance and crippling scarcity within a single 15-year span. Such acute anomalies provided concrete examples of climate extremity.