The country of Chad is home to nearly 15 million people and is an important economic and agricultural player in central Africa. With the Sahara Desert in the north and savannas in the south, the country straddles a transitional ecosystem known as the Sahelian belt, which stretches across the entire continent from Senegal to Sudan. Accordingly, cities in southern Chad tend to receive more rainfall while those farther north are typically drier. Recognizing the timing and geography of rainfall trends will be vital in the decades to come as temperatures rise globally and water and land management issues become increasingly important. However, the specifics of rainfall in the region—and how it is changing through time—are poorly understood.
Here Pattnayak et al. present records of rainfall between 1950 and 2014 for eight major cities in Chad: Abéché, Ati, Faya, Léré, Mongo, Moundou, N’Djamena, and Sarh. Faya is the only one of the eight cities in northern Chad, whereas Abéché, Ati, and Mongo are located centrally within the country and Léré, Moundou, and Sarh are in southern Chad. The capital city of N’Djamena, meanwhile, is the nearest of the eight cities to Lake Chad, a vital source of fresh water for tens of millions that’s situated along Chad’s western border.
As expected, cities in southern and central Chad—which are exposed to the seasonal West African monsoon—averaged substantially more rainfall than arid Faya, with Moundou, Mongo, and Sarh leading the way. The authors identified three distinct eras of rainfall within the time frame studied. In a wet period from 1950 to 1965, Chad generally saw significantly more rainfall than it did from 1966 to 1990. Then, from 1991 to 2014, rainfall began increasing again, except in Moundou and Léré, suggesting a potential recovery from the preceding dry period.
However, the recovery is not complete: Even in cities where rainfall totals have rebounded since the late 20th century, the precipitation is not falling at the same rate as in the midcentury wet period. And across the country overall, rainfall has decreased since 1950, particularly in the cities in southern Chad. Meanwhile, temperature has increased consistently in every city during the same time span, especially since 1985.
The authors noted that regional- and local-scale studies of precipitation and temperature like this one are vital for policy makers and stakeholders, allowing them to develop strategies and technologies to mitigate future problems. (Earth and Space Science, https://doi.org/10.1029/2019EA000619, 2019)
—David Shultz, Freelance Writer