Hydrological Response of Dry Afromontane Forest to Changes in Land Use and Land Cover in Northern Ethiopia

Belay Manjur Gebru,Sle-Gee Lee,Emnet Negash,Woo-Kyun Lee,Asia Khamzina

doi:10.3390/rs11161905

Abstract

This study analyzes the impact of land use/land cover (LULC) changes on the hydrology of the dry Afromontane forest landscape in northern Ethiopia. Landsat satellite images of thematic mapper (TM) (1986), TM (2001), and Operational Land Imager (OLI) (2018) were employed to assess LULC. All of the images were classified while using the maximum likelihood image classification technique, and the changes were assessed by post-classification comparison. Seven LULC classes were defined with an overall accuracy 83–90% and a Kappa coefficient of 0.82–0.92. The classification result for 1986 revealed dominance of shrublands (48.5%), followed by cultivated land (42%). Between 1986 and 2018, cultivated land became the dominant (39.6%) LULC type, accompanied by a decrease in shrubland to 32.2%, as well as increases in forestland (from 4.8% to 21.4%) and bare land (from 0% to 0.96%). The soil conservation systems curve number model (SCS-CN) was consequently employed to simulate forest hydrological response to climatic variations and land-cover changes during three selected years. The observed changes in direct surface runoff, the runoff coefficient, and storage capacity of the soil were partially linked to the changes in LULC that were associated with expanding bare land and built-up areas. This change in land use aggravates the runoff potential of the study area by 31.6 mm per year on average. Runoff coefficients ranged from 25.3% to 47.2% with varied storm rainfall intensities of 26.1–45.4 mm/ha. The temporal variability of climate change and potential evapotranspiration increased by 1% during 1981–2018. The observed rainfall and modelled runoff showed a strong positive correlation (R2 = 0.78; p < 0.001). Regression analysis between runoff and rainfall intensity indicates their high and significant correlation (R2 = 0.89; p < 0.0001). Changes were also common along the slope gradient and agro-ecological zones at varying proportions. The observed changes in land degradation and surface runoff are highly linked to the change in LULC. Further study is suggested on climate scenario-based modeling of hydrological processes that are related to land use changes to understand the hydrological variability of the dry Afromontane forest ecosystems.

Highlights

Forests provide multitudes of essential ecosystem services [1], such as soil nutrient cycling, build-up of organic matter, and water retention
The Forest Resource Assessment (FRA) that was completed by Food and Agriculture organization (FAO) in 2005 and preliminary results of FRA 2015 [5] indicate that, on a global scale, the total forest area continues to decrease by 3.1%, which is about 0.6% per year from 2000 to 2005 [3,6] and 3.3% per year from 2010 to 2015 [5]
Our study provides evidence of the significant land use and land cover (LULC) change in the watershed between the years 1986, 2001, and 2018

Summary

Introduction

Forests provide multitudes of essential ecosystem services [1], such as soil nutrient cycling, build-up of organic matter, and water retention. Deforestation continues at the highest rates across the tropics, and FRA estimates for 1990–2005 suggest annual rates of deforestation at 0.9% in South and Southeast Asia, 1.2% in Central America, 0.45% in South America, and 0.62% in Africa [3]. This means that, on average, each year from 1990 to 2015, an area of 4128–3999 million ha, which is above 3.1% of the tropical forest, was lost [3]. The change in land use is considered to contribute to 20% of global greenhouse gas emissions [7,8]. Forest degradation in sub-Saharan Africa is the main source of land-based emissions [9,10]

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