A mapping of the impact of soil erosion on the country has found it is losing billions in economic value as vast amounts of arable soil is washed away.
More than 745,000 hectares of agricultural land in Rwanda are potentially eroded every year, according to the study commissioned by the government’s Rwanda Water Resources Board (RWB) and the International Union for Conservation of Nature (IUCN).
Using a reference year of 2021A, the researchers show that 3 million tonnes crop produces are estimated to be lost seasonally or 6 million tonnes annually. From this amount, 22,000 tonnes of maize and 15,000 tonnes of beans are estimated to be lost every season due to severe erosion.
As a result, says the study, the total economic loss in agricultural productivity due to severe erosion in Rwanda is around Rwf 37.9 billion ($37.8million) every season.
In terms of the value of the topsoil loss, considering the national average is about 25t/ha/year, and the total area at risk of about 1,080,168 ha, or 45%% of the country total, the discharge is estimated to an average of 27 million ton of top soil lost annually.
Considering the market value of top soil in Rwanda, a proxy for soil productive capability, which is between US$34/tonne (RwF30,000) and US$57/tonne (RwF50,000); the annual loss is therefore estimated to be Rwf 810 billion on average, which is about one and half fold of what landscape restoration of the entire country would cost Rwf 513billion.
The results of the erosion control mapping shows that of the 30 districts of Rwanda, land under high erosion risk is about 1,080,168 hectares (45% of the total provinces land which is estimated to 2, 385, 830 hectares) of which 71 941 hectares (7% of the total risk areas) are at extremely high risk, 190, 433 hectares are at very high risk (18% of the total land at erosion risk), 300,805 hectares are at high risk (28% of the total risk identified), and 516,999 hectares (48% of the total land at risk) are at moderate risk.
Ngororero District has the highest risk with a total of 58,003 hectares i.e. 85% of its land at high erosion risk. Muhanga district is ranked the second-highest in erosion risk with 53, 352 hectares under risk (82% of the district land) while Rutsiro district comes third with 48,143 hectares prone to erosion estimated at 73% of the district land.
Other districts such as Karongi, Gakenke, Huye, Nyaruguru, Rulindo and Nyamagabe districts needs considerable attention as the risk accounts for more than 60% of the district land.
The observed erosive features in risk areas have shown that about 70,433 hectares (17% of the country land at risk) are affected by Gullies (39% of the affected land), severe gullies on 13,584 hectares (8% of the land affected land), landslides on 2,823 hectares (2% of the affected land) and rill erosion (93,831 hectares, i.e. 52% of the affected land).
To reverse this trend of destruction, the researchers estimate it could cost Rwanda Rwf 514 billion. At least Rwf 323 billion of the cost would be for protection of agricultural land against soil erosion (about 60% of the total risk areas) using Bench terraces, contour bank terraces known as progressive terraces and agroforestry and hey plantation on contour bank.
This would require about 8 years from 2022 to 2030 to complete the activity by investing about Rwf 42 billion every year to protect agricultural land against excessive erosion using community approach.