# Evaluating the impact of land use/cover changes on hydrological processes in the Lake Tana Basin

## TL;DR

This study shows how changes in land use over 17 years in the Lake Tana Basin affected water flow and other hydrological processes.

## Contribution

The study quantifies the impact of land use/cover changes on hydrology using SWAT modeling and two detailed LULC maps.

## Key findings

- Agricultural land decreased by 10.2% and forest cover by 33.1% between 2004 and 2021.
- Surface runoff increased by 5.8% while lateral flow and shallow aquifer evaporation decreased.
- Evapotranspiration remained stable, mainly due to lake evaporation.

## Abstract

Land use/cover (LULC) changes has a fundamental effect on the hydrological components in the Lake Tana Basin. The Lake Tana Basin, the source origin of the Blue Nile, has experienced notable LULC transitions over the past two decades. The present study evaluates the effect of land use/cover (LULC) changes on hydrological components in the Lake Tana basin using the soil and water assessment tool (SWAT). Two LULC maps, one from the International Livestock Research Institute (ILRI) for 2004 and another developed from Landsat 8 images for 2021, were used. Both models were calibrated and validated by SUFI-2 using observed discharge data, results showed strong performance (NSE > 0.79, R2 > 0.79 calibration; NSE > 0.90, R2 > 0.94 validation). Between 2004 and 2021, agricultural land decreased by 10.2% and forest cover declined by 33.1%, while wetlands and rangelands increased by 81.4 and 299.2%, respectively. Moreover, urban land was presented as a new class. These changes affected the basin’s hydrology as surface runoff increased from 111.6 to 118 mm/year (+ 5.8%), lateral flow decreased from 106.3 to 100.7 mm/year, and shallow aquifer evaporation declined by 10.2%. Evapotranspiration remained nearly constant at 1066 mm/year dominated by the lake evaporation. The results confirm the significant influence of LULC changes on the hydrological components of the Lake Tana Basin which highlight the need for sustainable land and water management.