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2 Acta Geophysica

2 2022

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Stream flow dynamics under current and future land cover conditions in Atsela Watershed, Northern Ethiopia

Gebretekle Haftu, Nigusse Amare Gebremedhin, Demissie Biadgilgn

Acta Geophysica

2022

Vol. 70, no 1

305--318

The aim of the present study was to detect land cover change for the last three decades and estimate its impact on stream flow dynamics under the current and future scenarios. Landsat satellite imageries were used for land cover classification for selected years (1987, 2002 and 2017). The effect of land cover change on stream flow was evaluated using SWAT model, and its performance was tested. The findings indicated significant land cover changes in the last three decades. Coverage of cultivated land (17%) and bare land (1%) in 1987 increased rapidly to 43 and 17% in 2017. Furthermore, there was 70% agreement between observed and simulated stream flow in both the calibration and validation phases. The stream flow of the watershed was changing significantly in response to land cover dynamics. The evaluation of hydrological response due to land cover change showed a monthly mean stream flow decrease by 12.7 m3 /s (−38%) in 1987 and 2017 in dry months. Nevertheless, it showed a monthly mean stream flow increase by 53.06 m3 /s (23%) in wet months. Similarly, between the years 2017 and 2047, the stream flow was estimated to increase by 42.84 m3 /s (15%) for wet months and a decrease by 13.52 m3 /s (−66%) for dry months. Generally, it can be concluded that land cover changes have significant impact on stream flow. Hence, establishing strong land use and water resource policies is an essential means for better evaluation and monitoring of water resource in the study area.

Geospatial solutions for evaluating the impact of the Tigray conflict on farming

Demissie Biadgilgn, Nyssen Jan, Annys Sofe, Negash Emnet, Gebrehiwet Tesfakiros, Abay Fetien, Wolf Eleonore

Acta Geophysica

2022

Vol. 70, no 3

1285--1299

Military conflicts strongly affect agricultural activities. This has strong implications for people’s livelihoods when agriculture is the backbone of the economy. We assessed the effect of the Tigray conflict on farming activities using freely available remote sensing data. For detecting greenness, a normalized difference vegetation Index (NDVI) was analyzed in Google Earth Engine (GEE) using Sentinel 2 satellite images acquired in the pre-war (2020) and during war (2021) spring seasons. CHIRPS data were analyzed in GEE to understand the rainfall conditions. The NDVI of 2020 showed that farmlands were poorly covered with vegetation. However, in 2021, vegetation cover existed in the same season. The NDVI changes stretched from −0.72 to 0.83. The changes in greenness were categorized as increase (2167 km2 ), some increase (18,386 km2 ), no change (1.6 km2 ), some decrease (8269 km2 ), and decrease (362 km2 ). Overall, 72% of the farmlands have seen increases in green vegetation before crops started to grow in 2021. Scattered patches with decreases in vegetation cover correspond to irrigation farms and spring-cropping rain-fed farms uncultivated in 2021. There was no clear pattern of changes in vegetation cover as a function of agro-climatic conditions. The precipitation analysis shows less rainfall in 2021 as compared to 2020, indicating that precipitation has not been an important factor. The conflict is most responsible for fallowing farmlands covered with weeds in the spring season of 2021. The use of freely accessible remote sensing data helps recognizing absence of ploughing in crisis times.