Abstract. Understanding responses by changes in land use and land cover
(LULC) and climate over the past decades on streamflow in the upper Blue
Nile River basin is important for water management and water resource
planning in the Nile basin at large. This study assesses the long-term
trends of rainfall and streamflow and analyses the responses of steamflow to
changes in LULC and climate in the upper Blue Nile River basin. Findings of
the Mann–Kendall (MK) test indicate statistically insignificant increasing
trends for basin-wide annual, monthly, and long
rainy-season rainfall but no
trend for the daily, short rainy-season, and dry season rainfall. The Pettitt test did
not detect any jump point in basin-wide rainfall series, except for daily
time series rainfall. The findings of the MK test for daily, monthly, annual, and
seasonal streamflow showed a statistically significant increasing trend.
Landsat satellite images for 1973, 1985, 1995, and 2010 were used for LULC
change-detection analysis. The LULC change-detection findings indicate
increases in cultivated land and decreases in forest coverage prior to 1995,
but forest area increases after 1995 with the area of cultivated land that decreased. Statistically, forest coverage changed from 17.4 % to 14.4%, by 12.2 %, and by 15.6 %, while cultivated land changed from 62.9 %
to 65.6 %, by 67.5 %, and by 63.9 % from 1973 to 1985, in 1995, and in
2010, respectively. Results of hydrological modelling indicate that mean
annual streamflow increased by 16.9 % between the 1970s and 2000s due to
the combined effects of LULC and climate change. Findings on the effects of LULC
change on only streamflow indicate that surface runoff and base flow are
affected and are attributed to the 5.1 % reduction in forest coverage and
a 4.6 % increase in cultivated land areas. The effects of climate change only
revealed that the increased rainfall intensity and number of extreme
rainfall events from 1971 to 2010 significantly affected the surface runoff
and base flow. Hydrological impacts by climate change are more significant
as compared to the impacts of LULC change for streamflow of the upper Blue
Nile River basin.
Improving SWAT model performance in the Upper Blue Nile River Basin using meteorological data integration and catchment scaling
