Efforts to tackle land degradation worldwide have spurred the adoption of soil and water conservation (SWC) practices intended to reduce surface runoff and erosion. Despite their widespread implementation, missing or incomplete monitoring remains a pervasive problem preventing evaluation of how well SWC practices meet these aims. When using runoff and sediment loss as main parameters to evaluate SWC efficacy, the key metrics are the production of flow per unit rainfall (runoff ratio), and exported sediment (sediment concentration). We develop a method to assess changes in these metrics in the absence of a flow rating curve, using more complete and reliable measurements of stage (flow depth). We apply these methods to datasets with incomplete rating curve collected from five watersheds included in the Tana and Beles Integrated Water Resource Development Project (TBIWRDP) in the Abay (Blue Nile) basin, Ethiopia. Changes in runoff ratio and sediment concentration relative to the first year of treatment varied by season. In the long wet season (Kiremt) that generates most runoff and erosion, reductions in runoff ratio and in sediment concentration occurred in four watersheds. Reductions in the runoff ratio were directly proportional to the areal density of SWC treatments in the watersheds, suggesting that SWC treatments were effective in controlling runoff and erosion.We suggest that stage and sediment concentration information can be used to assess watershed responses to SWC treatments. Focusing on these measurements, may facilitate the design of reliable and affordable monitoring programs, and ultimately facilitate improved financing approaches based on reasonable estimates of likely SWC practice performance.
The war in Tigray, Ethiopia has displaced millions of people and created a humanitarian crisis. However, the impacts of the conflict on cultivated land area and local food production remains poorly quantified, hindering aid efforts. We used Sentinel-2 satellite imagery and developed multiple cultivation detection criteria based on Normalized Difference Vegetation Index time series validated using field observations from 2021 and 2022. Significant net losses of well cultivated land in highland croplands (elevation ≥ 1200 m) were observed between 2019/20 (pre-war) and 2021 (in-war), with greater losses in areas with higher density of conflict incidents. Sub-regions with high estimated loss of well cultivated land also exhibited high numbers of internally displaced people (IDP), consistent with a causal effect of the conflict on land abandonment. Our study estimated that the kilocalories lost due to abandonment of croplands (excluding Western Tigray zone) could have supported about 1.2 times the recorded IDPs in the region.
<p>On November 4<sup>th</sup>, 2020 a deadly civil war broke out in Tigray, Ethiopia displacing close to 2 million people internally and more than 48,000 refugees in neighboring Sudan by August 2021<sup></sup>[1]. Given agriculture is the livelihood of millions of people in Tigray, evaluation of the conflict&#8217;s impact on cultivated land and the consequent crop production is critical for government and non-government disaster relief institutions. Unfortunately, such evaluation is extremely challenging as the conflict is characterized by communication blackout leaving the region without access to cellphone or internet.</p><p>In this study, we used Sentinel-2 and Planet satellite imagery data to map loss of well cultivated land in 2021 due to the war. We developed multiple cultivation detection criteria based on the peak and falling limb characteristics of Normalized Difference Vegetation Index (NDVI) time series, validated using limited field observations of fallow and cultivated plots from the wet season in 2021 and 2022. We employed object detection machine learning model to identify harvest piles as an additional parameter to detect farming activity.</p><p>Our predicted change in cultivation map from 2019/20 to 2021 showed that the density of conflict incidents was positively correlated to the mean net loss of well cultivated land with R<sup>2 </sup>of 0.7 in Tigray highlands (elevation > 1200 m). Sub-regions with high estimated net loss of cultivated land due to abandonment of reported internally displaced people also resulted in high predicted loss of well cultivated land using NDVI based criteria in our study. In the absence of extensive in situ data, we demonstrate how satellite imagery along with good understanding of local farming practices can provide timely and useful information to assist humanitarian management efforts in times of crisis and recovery phase.</p><p>[1] Annys, Sofie, Tim Vanden Bempt, Emnet Negash, Lars De Sloover, Robin Ghekiere, Kiara Haegeman, Daan Temmerman, and Jan Nyssen. <em>Tigray: Atlas of the Humanitarian Situation</em> (version 2.2). Zenodo, 2021. https://doi.org/10.5281/zenodo.5805687.</p>
Efforts to tackle land degradation worldwide have spurred the adoption of soil and water conservation (SWC) practices intended to reduce surface runoff and erosion. Despite their widespread implementation, missing or incomplete monitoring remains a pervasive problem preventing evaluation of how well SWC practices meet these aims. Key metrics to evaluate SWC efficacy are the production of flow per unit rainfall (runoff ratio), and exported sediment (sediment concentration). We develop a method to assess changes in these metrics in the absence of a flow rating curve, using more complete and reliable measurements of stage (flow depth). We apply these methods to incomplete monitoring datasets collected from five watersheds included in the Tana and Beles Integrated Water Resource Development Project (TBIWRDP) in the Abay (Blue Nile) basin, Ethiopia. Changes
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