The Science of Rainy Season and the Problem of Drought in Ethiopia

Rain rolling in from the southwest on the Guinea monsoon winds

The months of June to August in Ethiopia are rainy season, known locally as krempt.  It is during these three months that most of the country receives at least 90% of its total annual rainfall.  Rain is the distinguishing element of Ethiopia’s seasons.  Ethiopia’s two extreme seasons are rainy season between June and August and dry season between December and February.  Since I’ve spent the last 13 years in the American mid-west where annual precipitation is fairly evenly distributed across the seasons and temperature characterizes the extremes from summer to winter, I’ve been very curious about this rainy and dry season phenomenon in Ethiopia.  This issue of rain and the lack thereof is not just what characterizes Ethiopia’s seasons.  The lack of rain, or drought, and the shortages of food that go with drought, have become almost synonymous with Ethiopia in the minds of many people around the world.  This year has been no different with significant media attention on the drought and food crisis of the Horn of Africa, including parts of southeastern and southern Ethiopia.  So in an effort to better understand the science of Ethiopia’s rains and the problem of drought, I recently opened up an Ethiopian grade 10 geography book and turned to the chapter on weather and climate.

In the U.S., because the country is located north of the tropics, the prominent trade winds blow from west to east.  Thus when you turn on the weather channel in Chicago you’ll notice that most weather patterns move across the country in a roughly eastward direction.  Seasonal weather patterns in the mid-west of the U.S. are based mostly on latitude and the amount of direct sunlight received.  In Chicago, it is hot in the summer because the northern hemisphere is tilted sunward and Chicago receives more direct sunlight, while it is cold in the winter because the Earth has tilted in such a way that Chicago receives only indirect sunlight and far fewer hours of it.

Here in Ethiopia, because the country is located close to the Equator, there is only a small change between seasons when it comes to the amount or directness of sunlight.  Seasonal temperatures change relatively little and the change that does occur has more to do with cloud cover than directness of sunlight.  In fact, the coolest temperatures are during the time of year – June to August – when Ethiopia receives the most direct sunlight.  Because Ethiopia is located in the region between the tropics, the dominant trade winds move in a generally westward direction.  They are called easterlies, because they come out of the east. These easterlies play an important role in the seasonal patterns of Ethiopia.  There are also seasonal-only winds, called monsoon winds, the most prominent of which are the Guinea monsoon winds that blow over the central part of the African continent during June through August.  The Guinea monsoon winds actually blow against the dominant tropical trade winds, but blow strong enough that they account for most of the precipitation of Ethiopia during rainy season.

Ethiopia has four seasons.  The two extremes, like in North American, are summer – June through August – and winter – December through February.  Rather than temperature extremes, though, in Ethiopia the extremes are marked by amounts of rain.  The months of June through August are Ethiopia’s rainy season. The months of December through February are the dry season.  During dry season, it is extremely rare for most regions of Ethiopia to receive any precipitation at all.

During the months of June through August, because the direct sunlight hits near the Tropic of Cancer (north of Ethiopia), a large low-pressure air region develops and stays over North Africa (warmer air equals lower pressure air), while high-pressure air regions develop across and off the coasts of South Africa.  They develop both to the east of the continent in the Indian Ocean, and to the west of the continent in the Atlantic Ocean.  As a result of the high-pressure air region off the west coast of southern Africa and the low-pressure air region on land across the north of the continent, monsoon winds blow from the Gulf of Guinea, blowing in a northeastward direction, across the central part of the continent and the Sahel (atmospheric movement from high-pressure air to low-pressure air causes wind).  These Guinea monsoon winds, as defined by their name, are seasonal only and blow opposite to the dominant trade winds of the tropical region.  However, because of the large low-pressure air region over the northern part of the continent, these monsoon winds are strong enough to carry moisture from the Atlantic across the continent all the way east to Ethiopia and dump that moisture as rain across the Ethiopian highlands.  Meanwhile, the dominant trade winds – the easterlies – carry moisture from the Indian Ocean and the Gulf of Aden onto the African continent and shower Ethiopia as well.  Despite its closer proximity to the Indian Ocean, it is actually the strong monsoon winds from the Gulf of Guinea in the Atlantic that provide most of the rain to Ethiopia during rainy season.  Because of the cloud cover that these moisture-filled winds bring to Ethiopia, temperatures during rainy season are cooler than other times of the year.

During the months of December through February, because the southern hemisphere tilts sunward, direct sunlight hits considerably south of Ethiopia around the Tropic of Capricorn.  As a result of this direct sunlight and higher temperatures, low-pressure air regions develop over South Africa and in the Indian and Atlantic Oceans off the costs of the continent’s southern region.  The high-pressure air regions develop across North Africa and the Middle East.  As a result of these air pressure regions together with the dominant easterlies, a dry wind blows over Ethiopia from South Asia, the Middle East and the Arabian Peninsula.  These winds bring no precipitation at all, thus December through February is Ethiopia’s dry season.  The clear skies of this season account for the warmer days and cool nights received from December to February.

Between these two extreme seasons, some regions of Ethiopia can receive small amounts of rain.  The southern and southeastern regions sometimes receive small amounts of rain during September to November.  While the central and northern parts of Ethiopia usually receive small amounts of rain during March through May, which they call the “small rains.”  These autumn and spring rains are mostly as a result of easterlies bringing moisture off the Indian Ocean and the Gulf of Aden over the Horn of Africa.

Because Ethiopia’s seasons and rain amounts are so guided by air pressure regions and wind directions, there is great concern over the effects that climate change could bring to the country.  Because Ethiopia relies on basically one season for almost all of its annual rainfall, it is very prone to drought, crop failure, and food crisis.  If the rainy season doesn’t bring enough rain, or if the rains are too strong so that the soil can’t absorb the water and it simply runs off the hills, Ethiopia ends up in trouble because it can’t produce enough food to sustain the country through an entire calendar year.  Historically, Ethiopia has relied on small second crops during the “small rains” of March through May to get the population through the year, but if the “small rains” don’t come or don’t amount to enough to produce crop (as has been the case during a number of the recent years), the country’s food supply runs out before it can be replenished from the new crops that come at the end of the rainy season.  The cyclical rain problem is especially challenging for pastoralist regions.  If the smaller rains of the fall and/or spring don’t come at all, many animals can be lost when the land becomes too dry from December through May.  For communities who rely on those animals for their food and livelihood, the situation can become very touch and go.

In Ethiopia, one sometimes hears people refer to a “green drought.”  It’s a strange phenomenon, but people are often the hungriest during the greenest time of year, the rainy season, between June and August.  Just while everything is starting to grow anew, the country runs short of food from the previous harvest season.  So while people watch the new crops grow and await the harvest at the end of the rainy season, they often watch in fear as their personal food stores diminish, as the international agencies talk about regional food shortages, and as the government debates whether or not the national food reserves are sufficient (or whether the government sold off too much of the reserves as export to raise revenue).  As Ethiopians harvest in September, they hope that the crop will be plentiful enough to sustain the ever-growing Ethiopian population through another entire year.

This year there has been much international attention on the drought and food crisis of the Horn of Africa, including Somalia, parts of eastern Kenya and parts of the southeastern and southern regions of Ethiopia.  The regions hit hardest in Ethiopia have been the Somali federal state of the southeast and parts of the Oromo federal state in the south and southeast.  These regions include large numbers of pastoralist communities who have lost whole herds of animals because of drought and have therefore lost both their food and cash sources.  These are also regions that typically receive less rain even during good rain years, so they are regions more susceptible to drought and changing weather / climate patterns.  Since the heavy rains of Ethiopia’s rainy season come from the monsoon winds blowing in from the Gulf of Guinea in the west, the western highlands of Ethiopia tend to get the most rain.  By the time these rain-heavy monsoon winds get over the mountains to the lowland regions of Ethiopia’s east, their moisture is mostly spent.  The eastern and southeastern regions of the country, therefore, must rely on the less rain-heavy easterlies that come from the Gulf of Aden and the Indian Ocean.  In recent years, rain from these easterlies has been very unreliable.

These seasonal rain patterns in Ethiopia are an ancient phenomenon, as is the problem of drought.  The specter of climate change, however, stands to exacerbate the already persistent problem of drought in Ethiopia.  Furthermore, climate change stands to hurt some climates and countries much worse than others.  Countries like Ethiopia, which are economically underdeveloped and which rely from season to season on fragile weather and climate patterns, stand to suffer the most because of damage done to the planet and its reaction to that damage.  Regardless of what one thinks of the current government in Ethiopia, it’s been good to see the prime minister at the forefront as an outspoken representative for the African continent regarding this issue of climate change.

I would be wrong to not also point out that drought in Ethiopia is very region-by-region.  Many Ethiopians resent the image the world has of the country as a dry, famine stricken land.  While I don’t wish to diminish the horrible problem of drought in certain regions of the country (and it’s not always the same regions), most visitors to Ethiopia, especially during the summer and fall, would not see a famine stricken landscape.  Instead, in most parts of Ethiopia, including here in the Wolaita region, they would see gardens that can grow just about anything you want, green mountains rolling in all directions, streams rushing with water, and fruit trees everywhere; it’s a very lush, green and beautiful landscape.  This is one of the many ironies of Ethiopia.  It’s been called the “Water Tower of East Africa,” yet millions don’t have access to clean drinking water.  It’s been called the “Region’s Hydroelectric Generator,” yet the electric power flickers on and off constantly.  It’s a land of ancient Semitic languages and scripts, as old as Arabic and Hebrew, yet vast numbers of people are illiterate.  It was an ancient economic powerhouse, a key trading empire in the ancient Indian Ocean trading circuit, yet it’s now one of the poorest countries on the globe.  And it’s a land of “green drought,” where it can appear so lush and green, while people are suffering from shortages of food.

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