Climate and land use shifts alter Africa's Sudano-Sahelian dryland regions

Climate and land use shifts alter Africa's Sudano-Sahelian dryland regions
by Simon Mansfield
Sydney, Australia (SPX) Jul 19, 2023

A comprehensive understanding of the long-term vegetation dynamics and their potential influences in the Sudano-Sahelian region of Africa is pivotal in progressing sustainable management of these delicate dryland ecosystems. These trends and changes, particularly those not attributable to rainfall, need a more in-depth examination to decode the role of non-climatic factors like land use and land cover (LULC), as well as the impact of fires.

In a recent study published in Regional Environmental Change, meticulous examination of trends in vegetation greenness was carried out using satellite data from 2001 to 2020. This was done at the pixel scale across the Sudano-Sahelian region. The focus was to quantify the relative contributions of climatic and non-climatic factors, region by region.

This investigation was undertaken by the EOWATER team at the State Key Laboratory of Remote Sensing Science, under the aegis of the Aerospace Information Research Institute (AIR), and the Chinese Academy of Sciences (CAS).

The team utilized MODIS NDVI, a reliable indicator of vegetation greenness, as a cornerstone of their analysis. They found a general pattern of greening across the Sudano-Sahelian region. However, they also discovered areas of browning or vegetation loss, which were primarily concentrated in central West Africa.

To scrutinize rainfall-driven changes, a correlation-based attribution model was used. Surprisingly, their results indicated that only nearly half of the regions exhibiting vegetation greening could be attributed to long-term variations in rainfall. Conversely, most of the browning trends did not correspond to rainfall changes. The researchers found that these greening and browning trends, unrelated to rainfall, could likely be attributed to non-climatic factors, specifically changes in LULC and the influence of fires.

The impact of LULC changes on vegetation greenness was found to be locally significant in certain sub-regions of the Sudano-Sahelian. By examining the fractional abundance of LULC classes within each NDVI pixel, the study revealed that gains, represented by increases in LULC classes, in cropland and natural vegetation due to positive land management were the primary drivers of greening in Senegal and Ethiopia.

The team also discovered that the combined influence of rainfall variability and LULC changes contributed to greening trends in Mali and Sudan.

Conversely, the study noted that browning of vegetation in central West Africa was linked to the expansion of cropland and reduction of natural vegetation, typically associated with extensive agricultural activities. These findings underline the need for more sustainable natural resource management in the region, especially in light of ongoing population growth.

The study also found that repeated fires for agricultural expansion in central West Africa were compounding the browning of vegetation.

These findings provide a more nuanced understanding of vegetation dynamics in the Sudano-Sahelian drylands. It underscores the critical role of both climatic and non-climatic factors in shaping these ecosystems, which are facing mounting pressure due to the intensifying demand for land resources. These insights will be instrumental in guiding future efforts towards sustainable management and preservation of these fragile dryland ecosystems.

Research Report:Changes in vegetation greenness related to climatic and non-climatic factors in the Sudano-Sahelian region